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What is Daphnia? A quick overview

Daphnia is a genus of small planktonic Crustaceans under the Arthropoda Phylum. The body of a Daphnia is usually 0.2-6.0 mm (0.01-0.24 inches) long, which is pretty tiny compared to its cousins such as crab, lobster, crayfish, and shrimp. Daphnia species live in various aquatic environments ranging from acidic swamps to freshwater lakes and ponds. Daphnias are also called water fleas because their swimming style resembles the movements of fleas.

[In this image] A dark-field microscopic image of a Daphnia.
Image source: Wikimedia commons

[In this video] See microscopic crustaceans like Daphnia, Copepod, and Ostracod under the microscope.

Classification of Daphnia - the Phylum Arthropoda

Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Branchiopoda
Order: Anomopoda
Family: Daphniidae
Genus: Daphnia

Daphnia is a member of Phylum Arthropoda. Arthropods are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages (legs). Insects, spiders, scorpions, centipedes, mites, crabs, shrimps, daphnias, copepods, and trilobites (extinct) all belong to the enormous family of Arthropoda. Arthropoda owns the largest number of species among animals. They are very successful both on land, in water, and in the air.

[In this image] The huge family of Arthropods.

Daphnias can be classified under a subphylum called Crustacea. Crustaceans form a large, diverse group of aquatic animals such as crabs, lobsters, crayfish, shrimp, krill, prawns, woodlice, barnacles, copepods, amphipods, and mantis shrimp.

There are about 450 species of Daphnias distributed worldwide. The two most commonly found species are (smaller and most common) and (larger). D. pulex is a biological model species and was the first crustacean to have its genome sequenced.

[In this image] Two most common Daphnia species. Left: D. pulex with a body length around 1-2 mm. Right: a female D. magna with a clutch of eggs. It can grow up to 4 mm long.
Original images: D. pulex, D. magna

Where do Daphnias live?

Daphnias can be found in almost every nutrient-rich water body. A few species are marine, but generally, most Daphnias are freshwater organisms (in lakes and ponds).

Daphnias may move between different depths of the water column. They can move up to the algae-rich surface of the water (usually at night) and move down to the bottom of lakes to avoid predators (during the day). Their location is also controlled by seasonal variations depending on their food supply.

[In this image] Diel vertical migration of Daphnias.
Daphnias are smart and can learn how to avoid fish predation. (A) Daphnias remain in warm, nutritious water near the top layer of open water in the absence of predators. (B) Under predation, Daphnias migrate to deeper water strata, seeking refuge from fish predators. However, they migrate to nutrient-rich and warmer strata for feeding during the night.
Image source: Weiss LC., Front. Behav. Neurosci., 2019

Why we call Daphnia a planktonic animal?

Daphnias are too small and weak to live in a strong current, which they are unable to swim against. But they are light enough to stay suspended by using their legs and antennae for movement. This is why we classify Daphnia as a " planktonic animal", meaning they live mainly by drifting in the body of water.

We usually call all these planktonic animals drifting in oceans, seas, and freshwater " Zooplankton". In Greek, zoon means "animal" and "planktos" means "wanderer" or "drifter". Zooplankton includes single cellular protozoa, small crustaceans, and some juvenile mollusks, shrimps, crabs, or fishes. Zooplankton is the fundamental food source in a food chain, which plays a critical role in aquatic ecology.

[In this image] Many microscopic organisms constitute the fundament of the food chain in a water body. Daphnias feed on algae or bacteria. Then, they in turn are eaten by fish and aquatic insects. It seems that their role in life is to provide a snack for a larger organism.

Click the post below to learn more about different microscopic organisms in a drop of pond water.

The body structure of Daphnia

[In this image] An illustration of body parts of a Daphnia pulex.

Studying the anatomy of Daphnia is made easier by the fact that most of its outer shell is clear, showing most of the internal organs at work, including the beating heart.

[In this image] Daphnia magna under the microscope.

Carapace or shell

Daphnia's body is divided into segments (a common feature of Arthropods), although this division is not visible. Its body is covered by the two-valved carapace, a folded shell-like structure protecting its back. This exoskeleton is made up of chitin and calcium.

There is an abdominal gap of the carapace, in which the five or six pairs of legs lie. Overall, a Daphnia looks like a short and stout shrimp without body segments.

Head, compound eyes, and antennae

The head of a Daphnia contains a pair of darkly colored compound eyes and numerous antennae used for feeling and swimming. The number of ommatidia (or small eyes) that make up the compound eye varies from species to species - some species could have up to 300 ommatidia! Daphnia's eyes can move by the ciliary muscles.

[In this image] The comparison of compound eyes from a fruit fly and a Daphnia. Each compound eye consists of many ommatidia - from hundreds (insect's eyes) to 20 (Daphnia's eyes).
Image source: Left, Moment of Science; Right, Semantic scholar

The first antenna is smaller and located close to its mouth, which creates a motion bringing the food particles into the month. The second antenna is much bigger and used for swimming. Each of the second pair of antennae has two branches, and both branches bear long, feathery bristles.

[In this image] Zoom in to see the detail of Daphnia's head.
Image source: New World Encyclopedia

Body

The thorax of water fleas is very short and hard to tell. There are five or six pairs of thoracopods (or thoracic appendixes) on its abdominal side, which move like the rows of legs under a shrimp.

Daphnia has a primitive digestion system, including the mouth, intestine, and anus. Near its anus, Daphnia uses two hook-like cuticular claws (postabdominal claws) to clear debris out of the carapace.

[In this image] A mounted Daphnia pulex, which was stained with a red dye, shows you its side view.

Heart

Daphnia's heart is at the top of the back, just behind the head. Under normal conditions, it can beat at an average heart rate of 180 beats per minute.

[In this video] Heart beating of a Daphnia.

Daphnia has an open circulatory system. Instead of having blood vessels, Daphnia has a fluid called hemolymph and blood cells. Under a microscope, you can even see blood cells being pumped throughout the body cavity by the simple heart.

[In this image] Daphnias can produce hemoglobin to adapt to low-oxygen environments. Pale (left) or bright red (right) Daphnia, depending on whether they live in O2-rich or O2-poor water. The color change reflects how much hemoglobin the animals are synthesizing.
Image source: Shinichi Tokishita

Nervous system

Daphnia's nervous system consists of a brain and paired nerve cords. Like many animals, Daphnia's nervous system can be affected by chemicals. Due to the translucent shell and the visibly altered heart rate, scientists performed many experiments on Daphnia to study the increase in the heart rate by giving Daphnia alcohol, caffeine, nicotine, or adrenaline.

Reproductive system

Daphnia males are generally smaller than females but have longer antennae and a modified postabdomen. Daphnia females have a brood chamber located between the body wall and dorsal surface of the carapace used to carry their eggs.

[In this image] A female Daphnia with eggs. Its carapace is nearly translucent, so we can observe the internal organs, including the heart, intestine, and eggs under the microscope.
Image source: wiki

How does a Daphnia eat?

Daphnias are filter feeders, meaning that they do not actively seek food. As they swim, they filter even tinier organisms from the water. They feed on single-celled algae, yeasts, and bacteria. They also eat small organic particulates from decomposed plants.

Daphnias are often used to clean fish tanks of algae "bloom" because their diet consists of very small algae particles. A few bigger Daphnia species are carnivorous and prey on other water fleas.

How does a Daphnia swim?

Daphnias are also called common water fleas because of their general appearance and jerky hopping motion which resembles that of the land fleas. Swimming is powered mainly by the second set of antennae, which are larger in size than the first set.

[In this video] Water fleas (Daphnia sp.) swimming like hopping.

Daphnia's life cycle and reproduction

Under favorable environmental conditions (usually in the spring until the end of the summer), Daphnias reproduce parthenogenetically to expand their population rapidly. Parthenogenesis is a form of asexual reproduction in which the offspring develop from unfertilized eggs. Parthenogenesis is common in insects and spiders, and also occurs in some species of fish, amphibians, and reptiles.

One female Daphnia can carry 50 or so eggs in the brood chamber. These unfertilized eggs are nurtured in the brood chamber inside the mother Daphnia's carapace. The newly hatched Daphnia babies must molt several times before they are fully grown. This process usually takes about two weeks.

[In this image] Inside the mother Daphnia's brood chamber, new Daphnias grow by molting. When they are released, the young ones are fully grown small copies of the adult.
Image source: modified from Sumiya E. et.al., J of Applied Toxicology, 2016

[In this image] A stained Daphnia pulex juvenile has a single compound eye.

Fully mature females can produce a new brood of young about every ten days under ideal conditions. The reproduction process continues while the environmental conditions continue to support their growth.

[In this image] A Daphnia giving birth to young Daphnia.
Image source: wiki

When winter or other harsh environmental conditions approach, the parthenogenetic reproduction ceases, and male Daphnias are produced. Males tend to be much smaller in size than females. However, even in harsh environmental conditions, males may make up considerably less than half the population. Sexual reproduction by mating generates fertilized eggs, also called winter eggs, and are provided with an extra shell layer called ephippium. The extra layer preserves and protects the egg inside from harsh environmental conditions until the more favorable times, such as spring when the reproductive cycle can take place once again.

[In this image] Resting egg pouch (ephippium) and the juvenile Daphnia that just has hatched from it.
Image source: wiki

[In this image] The life cycle of Daphnia magna - The decision to go through either parthenogenetic or sexual reproductions is made based on environmental conditions.
Image source: wiki

How does a Daphnia grow?

Like all Crustaceans, Daphnia's shell cannot grow, so they need to molt as the animal grows larger. Because the carapace is used for protection, a new shell is usually grown under the old for the organism to be shielded at all times. The old carapace is discarded, and the animal rapidly absorbs water into the new shell, producing a stage of very rapid growth called an instar. This is especially prominent in juveniles, which can double their size from one instar to the next. The absorbed water is later gradually replaced by tissue.

[In this video] Daphnia's ecdysis or molting.
Notice the big one coming out of its carapace.

Daphnias are amazing transformers!

Daphnia can also avoid predators in a process called Cyclomorphosis in which it changes its size and shape to be more difficult to be eaten. The size is often predator-specific as they become larger or smaller to avoid consumption by the many types of fish that use Daphnias as their primary food source. A decrease in size is common when levels of the adult fish population are high, making the Daphnia harder for the larger organisms to see. Similarly, an increase in size is common when the levels of juvenile fish are high, making the Daphnias more difficult for these smaller fish to eat.

Several other environmental factors can also trigger cyclomorphosis, including the seasonal change of water temperature, sun period, current turbulence, and food abundance. Some Daphnia species can totally change their shape and elongate their body by extending the head to form a helmet and increasing the apical spine length.

[In this image] Four paired of Daphnias showing the morphological defenses by cyclomorphosis. Undefended morphotypes are displayed on the left side, and the defended morphotypes on the right side. You can see they are growing structures like a helmet or spike to make the predators hard to eat them.
Image source: Weiss LC., Front. Behav. Neurosci., 2019

The importance of Daphnias

Daphnias are a popular live food in tropical and marine fish keeping. Ecologically, Daphnias are at the bottom of the food chain pyramid, consuming algae and bacteria, and then being prey for small fish and carnivorous aquatic insects. The population of Daphnias is routinely used to measure the healthiness of aquatic habitats. For example, due to the sensitivity of water temperature, Daphnia is an indicator species commonly used to test climate change aspects.

Daphnias also make model organisms for biological study. The translucent carapace makes them excellent subjects for the microscope as one can observe the beating heart. As we mentioned above, scientists had used Daphnia to study several chemicals and observe an increase in heart rate.

[In this video] Even under relatively low-power microscopes, the heart beating of a Daphnia can be easily observed. Scientists took this advantage and used Daphnia to study the effects of Caffeine on the heart rate of Daphnia magna.

Daphnia's short reproductive cycle of only 8-10 days makes it ideal for experimental genetics. Many laboratories are studying the functions of genes and the evolution among arthropods using Daphnia's genome. Daphnia pulex was the first crustacean to have its genome sequenced. Its genome contains 31,000 genes - 8,000 more than the human genome (~ 25,000 genes)!

Daphnia even has a parasite disease. A bacterial parasite called Pasteuria ramosa infects Daphnia magna and transmits within Daphnia's population.

Summary

1. Daphnia is a genus of small planktonic Crustaceans under the Arthropoda Phylum. Its body is usually 0.2-6.0 mm long and is enclosed in a transparent shell. Daphnias are also called water fleas because their swimming style resembles the movements of fleas.

2. Daphnias are filter feeders, meaning that they do not actively seek food. As they swim, they filter single-celled algae, yeasts, and bacteria.

3. Daphnia's body is divided into segments. It has a transparent carapace (shell), head, compound eyes, antennae, heart, intestine, nervous system, and reproductive system.

4. Under favorable environmental conditions, Daphnia produces their progeny through asexual reproduction in which the offspring develop from unfertilized eggs ( Parthenogenesis). When winter or other harsh environmental conditions approach, sexual reproduction occurs. Mating generates fertilized eggs, which also contain an extra shell layer to protect the egg inside from harsh environmental conditions until the more favorable condition comes.

5. Daphnia avoids predators by changing its size and shape, a morphological defense called cyclomorphosis.

6. Daphnias are a popular food for tropical and marine fish. They are at the bottom of the food chain pyramid, consuming algae and bacteria. Daphnia is an indicator species commonly used to test climate change aspects.

7. Daphnias is a good model organism for biological study. The translucent shell makes them excellent subjects for the microscope because we can observe the beating heart. Scientists had used Daphnia to study several chemicals' impact on heart rate.

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Daphnia - Biology, Classification, Characteristics, and Reproduction

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Daphnia is a genus of small planktonic Crustaceans under the Arthropoda Phylum. The body of a Daphnia is usually 0.2-6.0 mm (0.01-0.24 inches) long, which is pretty tiny compared to its cousins such as crab, lobster, crayfish, and shrimp. Daphnia species live in various aquatic environments ranging from acidic swamps to freshwater lakes and ponds.

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(Image credit: Getty Images)

Paramecium or paramecia are single-celled protists that are naturally found in aquatic habitats. They are typically oblong or slipper-shaped and are covered with short hairy structures called cilia. Certain paramecia are also easily cultured in labs and serve as useful model organisms (a non-human species used to understand biological processes).

Appearance

Paramecia cells are elongated in appearance, and based on this shape were divided into two groups: aurelia and bursaria, according to the " The Biology of Paramecium, 2nd Ed. (opens in new tab)" (Springer, 1986). The aurelia morphological type is oblong, or "cigar" shaped, with a somewhat tapered posterior end. Bursaria, on the other hand, represents cells that are "slipper" shaped. They tend to be shorter, and their posterior end is rounded.

Paramecia can move forward at rates up to 2 millimeters per second, according to the " Cell Physiology Source Book" (opens in new tab)(Academic Press, 1995). Sometimes the organism will perform "avoidance reactions" by reversing the direction in which the cilia beat. This results in stopping, spinning or turning, after which point the paramecium resumes swimming forward. If multiple avoidance reactions follow one another, it is possible for a paramecium to swim backward, though not as smoothly as swimming forward.

Cilia also aid in feeding by pushing food into a rudimentary mouth opening, known as the oral groove. Paramecia feed primarily on bacteria, but are known to eat , unicellular algae and even some non-living substances such as milk powder, starch and powdered charcoal, according to "Biology of Paramecium."

(Image credit: Getty Images)

Cell structure

Paramecium are eukaryotes. In contrast to prokaryotic organisms, such as bacteria and archaea, eukaryotes have well-organized cells. The defining features of eukaryotic cells are the presence of specialized membrane-bound cellular machinery called organelles and the nucleus, which is a compartment that holds , according to Washington University (opens in new tab). Paramecia have many organelles characteristic of all eukaryotes, such as the energy-generating mitochondria. However, the organism also contains some unique organelles.

Under an external covering called the pellicle is a layer of somewhat firm cytoplasm called the ectoplasm. This region consists of spindle-shaped organelles known as trichocysts. When they discharge their contents, they become long, thin and spiky, according to "Biology of Paramecium."

Trichocysts are a network of telescopic organelles that are used to repel and shield from any predatory attacks and propel the paramecium in unpredictable directions, according to Cell Biology magazine (opens in new tab). Research published in the journal Zoological Science (opens in new tab) found that trichocysts of Paramecium tetraurelia were effective against two of the three predators that were tested: the Cephalodella species of rotifers and the Eucypris species of arthropods.

Below the ectoplasm lies a more fluid type of cytoplasm: the endoplasm. This region contains the majority of cell components and organelles, including vacuoles. These are membrane-enclosed pockets, which in plants and animals handle waste product, store water and offer structural support for cells, according to the National Human Genome Research institute (opens in new tab) Vacuoles take on specific functions with a paramecium cell. Food vacuoles encapsulate food consumed by the paramecium, according to the University of Chicago (opens in new tab). They then fuse with organelles called lysosomes, whose break apart food molecules and conduct a form of digestion. Contractile vacuoles are responsible for osmoregulation, or the discharge of excess water from the cell, according to the authors of " Advanced Biology, 1st Ed. (opens in new tab)" (Nelson, 2000). Depending on the species, water is fed into the contractile vacuoles via canals, or by smaller water-carrying vacuoles. When the contractile vacuole collapses, this excess water leaves the paramecium body through a pore in the pellicle.

Perhaps the most unusual characteristic of paramecia is their nuclei. " Paramecium along with the other ciliates have this rather unique feature," said James Forney, a professor of biochemistry at Purdue University. "They have two types of nuclei, which differ in their shape, their content and function."

The two types of nuclei are the micronucleus and macronucleus, according to the Encyclopedia of Microbiology (opens in new tab). The micronucleus is diploid; that is, it contains two copies of each paramecium chromosome. Forney notes that the micronucleus contains all of the DNA that is present in the organism. "It's the DNA that is passed from one generation to the another during sexual reproduction," he said. On the other hand, the macronucleus contains a subset of DNA from the micronucleus, according to Forney. "It is the transcriptionally active nucleus," he added. "So it's the nucleus that is transcribed to make mRNAs and proteins from those mRNAs." The macronucleus is polyploid, or contains multiple copies of each chromosome, sometimes up to 1000 copies, according to Encyclopedia of Microbiology .

(Image credit: Designua Shutterstock )

All paramecium species have one macronucleus, according to Forney. However the number of micronuclei can vary by species. He gives the example of the Paramecium aurelia species complex, which have two micronuclei and Paramecium multimicronucleatum, which have several.

Why the presence of two distinct nuclei? One evolutionary reason is that it is a mechanism by which paramecium and other ciliates can stave off genetic intruders: pieces of DNA that embed themselves into the genome. "In the case of ciliates, there's a mechanism in which, if a piece of DNA is in the micronucleus but it's not in the macronucleus, it will be removed from the next macronucleus that is made," Forney explained. "In other words, if something foreign got into the micronuclear genome, then when the next macronucleus is made, it would removed and not included in the expressed version [transcribed] of the genome." Forney notes that this has been described by some as a primitive DNA immune system; that is, surveying the genome and trying to keep out invading elements.

Reproduction

Paramecia can reproduce either asexually or sexually, depending on their environmental conditions. Asexual reproduction takes place when ample nutrients are available, while sexual reproduction takes place under conditions of starvation. In addition, paramecia can also undergo "autogamy" or self-fertilization under conditions of prolonged starvation, according to " Building the Most Complex Structure on Earth (opens in new tab)" (Elsevier, 2013)
Asexual reproduction (binary fission)
During binary fission, one paramecium cell divides into two genetically identical offspring, or daughter cells. According to Forney, the micronucleus undergoes mitosis, but the macronucleus divides another way, called an amitotic, or non-mitotic, mechanism. "It is not based on mitosis but it [macronucleus] divides between the two cells and somehow is able to keep approximately the same number of copies of each gene," he said.
Sexual reproduction (conjugation)
Conjugation among paramecia is akin to mating. Forney said that there are two mating types for paramecia, which are referred to as odd and even. This reflects the fact that the mating types for various paramecium species are denoted by either an odd or even number. For example, according to Forney, Paramecium tetraurelia have mating types 7 and 8. "Odd will mate with the even mating type but you cannot mate if you are the same mating type," he said. Moreover, only cells within a single Paramecium species can mate with one another.

The process is easily distinguishable under laboratory conditions. "The cells stick together. They can actually form rather dramatic clumps of cells when they are initially mixed," Forney said. "Then those gradually pair off into individual pairs in culture."

(Paramecium conjugation. Antonio Guillén, CC BY 3.0)

During sexual reproduction, the micronuclei of each paramecium undergo meiosis, ultimately halving the genetic content to create a haploid nucleus. These are exchanged between the two connected mates. The haploid nuclei from each mate fuse to create a new, genetically varied, micronucleus. In turn, the new micronucleus replicates to give rise to a new macronucleus.
Autogamy (self-fertilization)
"Autogamy is essentially the same thing as conjugation, but it is only happening with a single cell," Forney said. During this process, the micronucleus replicates multiple times. One of these new micronuclei undergo rearrangement of their genetic content. Some DNA is fragmented and some DNA sequences, known as "Internal Eliminated Sequences," are removed, according to the journal Cellular and Molecular Life Sciences (opens in new tab).

Classification

The general term "paramecium" refers to a single organism within the genus Paramecium. A genus, refers to a closely related group of organisms that share similar characteristics, according to Encyclopedia Britannica (opens in new tab). The genus Paramecium is further divided in groups known as subgenera, which each contain one or more species.

The methods of classifying paramecia have changed over the years. The earliest methods were through visual observation and were based on morphology, ultimately describing all paramecia as either aurelia or bursaria. More recently, classification has combined morphological observation with molecular and genetic information. This has helped to develop a family tree, known as a phylogenetic tree, that represents evolutionary relationships, according to Berkeley University (opens in new tab).

This shift from morphology to molecular phylogenetics has affected the understanding of relationships within the Paramecium genus and species diversity, according to Michaela Strüder-Kypke (opens in new tab), manager of advanced light microscopy at the Molecular and Cellular Imaging Facility at the University of Guelph in Ontario, Canada. There are five subgenera of paramecia in total ; Chloroparamecium, Helianter, Cypriostomum, Viridoparamecium and Paramecium, according to the journal Diversity (opens in new tab).

Strüder-Kypke said that a method of identifying species known as "DNA barcoding" has been used for Paramecium. "Identification of species based on the sequence of a particular fragment of DNA has been referred to as DNA barcoding," she explained. "Just like a barcode in the stores identifies each product, a short DNA sequence that is sufficiently divergent, can identify each species." One such barcode, the cox1 gene, has been "extensively utilized for the genus Paramecium," Strüder-Kypke said.

There are currently 19 recognized morphospecies of Paramecium, according to Strüder-Kypke. She explained that a morphospecies is a species defined only by distinct morphological characteristics, not by genetics or the ability to produce fertile offspring. Of this, 15 sibling species form what is known as the Paramecium aurelia species complex. Sibling species, according to Strüder-Kypke, look alike with no morphologically distinguishing characteristics, but they differ in biochemical and genetic aspects and cannot conjugate with one another. The Paramecium aurelia complex counts as a single morphospecies.

(Image credit: Luis Fernández García/CC BY 3.0)

New insights into Paramecium taxonomy and the existence of new species continue to be described even today. The 19th morphospecies,Paramecium buetschlii, was discovered in a freshwater pool in Norway and described in a research published in the journal Organisms Diversity & Evolution (opens in new tab). The same paper also described three new "cryptic species" found in Germany, Hungary and Brazil. The authors explain that they were treated as cryptic species because they were difficult to distinguish morphologically from other members of theParamecium genus. However, taxonomic markers in their DNA [DNA barcodes] indicate that they are a separate species.

"The idea is that, if we look in unusual habitats or "under sampled" regions of this world, we may still find new species," Strüder-Kypke told LiveScience.

Microorganisms, such as paramecium, can be useful tools to monitor water quality, as researchers from the Singapore University of Technology and Design (opens in new tab) (SUTD) have discovered. To measure pollutants in marine environments, the researchers tracked the movement of paramecium. "We chose paramecia because they are ubiquitous in water bodies and large enough to be seen with a normal camera," Assistant Professor Javier Fernandez at the Fermart Lab at SUTD said in a statement (opens in new tab). By tracking swimming speeds and movements, researchers were able to accurately detect the quality and presence of water pollutants, such as concentrations of heavy metals, in a sample. Paramecium swimming speeds declined when pollutants such as heavy metals zinc chloride and copper sulfate and some antibiotics such as erythromycin, were present.

"Taking a sample of water and measuring the speed of paramecia can therefore be used as a straightforward method to assess the drinkability of water without the need for specialised equipment or chemicals," said Fernandez. "Usually, you would need a different test for each pollutant, but paramecia swimming is a global measurement."

Additional resources

For more information about paramecium, check out " Endosymbionts in Paramecium (Microbiology Monographs Book 12) (opens in new tab)" by Masahiro Fujishima and " Brock Biology of Microorganisms (opens in new tab)". To watch paramecium in action take a look at this video (opens in new tab) produced by the YouTube channel Journey to the Microcosmos.

Bibliography

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(Image credit: Getty Images) Paramecium or paramecia are single-celled protists that are naturally found in aquatic habitats. They are typically oblong or slipper-shaped and are covered with short hairy structures called cilia. Certain paramecia are also easily cultured in labs and serve as useful model organisms (a non-human species used to understand biological processes).

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Daphnia , a genus of small planktonic crustaceans, are 0.2-5 millimetres (0.01-0.20 in) in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory ( Wiktionary) swimming style resembles the movements of fleas.

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Paramecium ( PARR-ə-MEE-sh(ee-)əm, -⁠see-əm; also spelled Paramoecium) is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. Paramecia are widespread in freshwater, brackish, and marine environments and are often very abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, it has been widely used in classrooms and laboratories to study biological processes. Its usefulness as a model organism has caused one ciliate researcher to characterize it as the " white rat" of the phylum Ciliophora.

Paramecia were among the first ciliates to be seen by microscopists, in the late 17th century. They were probably known to the Dutch pioneer of protozoology, Antonie van Leeuwenhoek, and were clearly described by his contemporary Christiaan Huygens in a letter of 1678. The earliest known illustration of a Paramecium was published anonymously in Philosophical Transactions of the Royal Society, in 1703.

In 1718, the French mathematics teacher and microscopist Louis Joblot published a description and illustration of a microscopic poisson (fish), which he discovered in an infusion of oak bark in water. Joblot gave this creature the name "Chausson", or "slipper", and the phrase "slipper animalcule" remained in use as a colloquial epithet for Paramecium, throughout the 18th and 19th centuries.

The name "Paramecium" - constructed from the Greek ( paramēkēs, "oblong") - was coined in 1752 by the English microscopist John Hill, who applied the name generally to "Animalcules which have no visible limbs or tails, and are of an irregularly oblong figure". In 1773, O. F. Müller, the first researcher to place the genus within the Linnaean system of taxonomy, adopted the name Paramecium, but changed the spelling to Paramœcium. C. G. Ehrenberg, in a major study of the infusoria published in 1838, restored Hill's original spelling for the genus name, and most researchers have followed his lead.

Species of Paramecium range in size from 50 to 330 micrometres (0.0020 to 0.0130 in) in length. Cells are typically ovoid, elongate, foot- or cigar-shaped.

The body of the cell is enclosed by a stiff but elastic structure called the pellicle. This consists of the outer cell membrane (plasma membrane), a layer of flattened membrane-bound sacs called alveoli, and an inner membrane called the epiplasm. The pellicle is not smooth, but textured with hexagonal or rectangular depressions. Each of these polygons is perforated by a central aperture through which a single cilium projects. Between the alveolar sacs of the pellicle, most species of Paramecium have closely spaced spindle-shaped trichocysts, explosive organelles that discharge thin, non-toxic filaments, often used for defensive purposes.

Typically, an anal pore (cytoproct) is located on the ventral surface, in the posterior half of the cell. In all species, there is a deep oral groove running from the anterior of the cell to its midpoint. This is lined with inconspicuous cilia which beat continuously, drawing food inside the cell. Paramecia live mainly by heterotrophy, feeding on bacteria and other small organisms. A few species are mixotrophs, deriving some nutrients from endosymbiotic algae ( chlorella) carried in the cytoplasm of the cell.

Osmoregulation is carried out by contractile vacuoles, which actively expel water from the cell to compensate for fluid absorbed by osmosis from its surroundings. The number of contractile vacuoles varies from one, to many, depending on species.

A Paramecium propels itself by whiplash movements of the cilia, which are arranged in tightly spaced rows around the outside of the body. The beat of each cilium has two phases: a fast "effective stroke", during which the cilium is relatively stiff, followed by a slow "recovery stroke", during which the cilium curls loosely to one side and sweeps forward in a counter-clockwise fashion. The densely arrayed cilia move in a coordinated fashion, with waves of activity moving across the "ciliary carpet", creating an effect sometimes likened to that of the wind blowing across a field of grain.

The Paramecium spirals through the water as it progresses. When it happens to encounter an obstacle, the "effective stroke" of its cilia is reversed and the organism swims backward for a brief time, before resuming its forward progress. This is called the avoidance reaction. If it runs into the solid object again, it repeats this process, until it can get past the object.

It has been calculated that a Paramecium expends more than half of its energy in propelling itself through the water. This ciliary method of locomotion has been found to be less than 1% efficient. This low percentage is nevertheless close to the maximum theoretical efficiency that can be achieved by an organism equipped with cilia as short as those of the members of Paramecium.

Paramecia feed on microorganisms like bacteria, algae, and yeasts. To gather food, the Paramecium makes movements with cilia to sweep prey organisms, along with some water, through the oral groove (vestibulum, or vestibule), and into the cell. The food passes from the cilia-lined oral groove into a narrower structure known as the buccal cavity (gullet). From there, food particles pass through a small opening called the cytostome, or cell mouth, and move into the interior of the cell. As food enters the cell, it is gathered into food vacuoles, which are periodically closed off and released into the cytoplasm, where they begin circulating through the cell body by the streaming movement of the cell contents, a process called cyclosis or cytoplasmic streaming. As a food vacuole moves along, enzymes from the cytoplasm enter it, to digest the contents. As enzymatic digestion proceeds, the vacuole contents become more acidic. Within five minutes of a vacuole's formation, pH of its contents drops from 7 to 3. As digested nutrients pass into the cytoplasm, the vacuole shrinks. When the vacuole, with its fully digested contents, reaches the anal pore, it ruptures, expelling its waste contents to the environment, outside the cell.

Some species of Paramecium form mutualistic relationships with other organisms. Paramecium bursaria and Paramecium chlorelligerum harbour endosymbiotic green algae, from which they derive nutrients and a degree of protection from predators such as Didinium nasutum. Numerous bacterial endosymbionts have been identified in species of Paramecium. Some intracellular bacteria, known as Kappa particles, give Paramecia that have them the ability to kill other strains of Paramecium that lack Kappa.

The genome of the species Paramecium tetraurelia has been sequenced, providing evidence for three whole- genome duplications.

In some ciliates, like Stylonychia and Paramecium, only UGA is decoded as a stop codon, while UAG and UAA are reassigned as sense codons (that is, codons that code for standard amino acids), coding for the amino acid glutamic acid.

The question of whether Paramecia exhibit learning has been the object of a great deal of experimentation, yielding equivocal results. However, a study published in 2006 seems to show that Paramecium caudatum may be trained, through the application of a 6.5 volt electric current, to discriminate between brightness levels. This experiment has been cited as a possible instance of cell memory, or epigenetic learning in organisms with no nervous system.

Reproduction

Like all ciliates, Paramecium has a dual nuclear apparatus, consisting of a polyploid macronucleus, and one or more diploid micronuclei. The macronucleus controls non-reproductive cell functions, expressing the genes needed for daily functioning. The micronucleus is the generative, or germline nucleus, containing the genetic material that is passed along from one generation to the next.

Paramecium reproduction is asexual, by binary fission, which has been characterized as "the sole mode of reproduction in ciliates" ( conjugation being a sexual phenomenon, not directly resulting in increase of numbers). During fission, the macronucleus splits by a type of amitosis, and the micronuclei undergo mitosis. The cell then divides transversally, and each new cell obtains a copy of the micronucleus and the macronucleus.

Fission may occur spontaneously, in the course of the vegetative cell cycle. Under certain conditions, it may be preceded by self-fertilization ( autogamy), or it may immediately follow conjugation, in which Paramecia of compatible mating types fuse temporarily and exchange genetic material.

Conjugation

In ciliates such as Paramecium, conjugation is a sexual phenomenon that results in genetic recombination and nuclear reorganization within the cell. During conjugation, two Paramecia of a compatible mating type come together and a bridge forms between their cytoplasms. Their respective micronuclei undergo meiosis, and haploid micronuclei are exchanged over the bridge. Following conjugation, the cells separate. The old macronuclei are destroyed, and both post-conjugants form new macronuclei, by amplification of DNA in their micronuclei. Conjugation is followed by one or more "exconjugant divisions".

Stages of conjugation

In Paramecium caudatum, the stages of conjugation are as follows (see diagram at right):

1. Compatible mating strains meet and partly fuse

2. The micronuclei undergo meiosis, producing four haploid micronuclei per cell.

3. Three of these micronuclei disintegrate. The fourth undergoes mitosis.

4. The two cells exchange a micronucleus.

5. The cells then separate.

6. The micronuclei in each cell fuse, forming a diploid micronucleus.

7. Mitosis occurs three times, giving rise to eight micronuclei.

8. Four of the new micronuclei transform into macronuclei, and the old macronucleus disintegrates.

9. Binary fission occurs twice, yielding four identical daughter cells.

In the asexual fission phase of growth, during which cell divisions occur by mitosis rather than meiosis, clonal aging occurs leading to a gradual loss of vitality. In some species, such as the well studied Paramecium tetraurelia, the asexual line of clonally aging Paramecia loses vitality and expires after about 200 fissions if the cells fail to undergo autogamy or conjugation. The basis for clonal aging was clarified by transplantation experiments of Aufderheide in 1986. When macronuclei of clonally young Paramecia were injected into Paramecia of standard clonal age, the lifespan (clonal fissions) of the recipient was prolonged. In contrast, transfer of cytoplasm from clonally young Paramecia did not prolong the lifespan of the recipient. These experiments indicated that the macronucleus, rather than the cytoplasm, is responsible for clonal aging. Other experiments by Smith-Sonneborn, Holmes and Holmes, and Gilley and Blackburn demonstrated that, during clonal aging, DNA damage increases dramatically. Thus, DNA damage in the macronucleus appears to be the cause of aging in P. tetraurelia. In this single-celled protist, aging appears to proceed as it does in multicellular eukaryotes, as described in DNA damage theory of aging.

When clonally aged P. tetraurelia are stimulated to undergo meiosis in association with either conjugation or automixis, the genetic descendants are rejuvenated, and are able to have many more mitotic binary fission divisions. During either of these processes, the micronuclei of the cell(s) undergo meiosis, the old macronucleus disintegrates and a new macronucleus is formed by replication of the micronuclear DNA that had recently undergone meiosis. There is apparently little, if any, DNA damage in the new macronucleus. These findings further solidify that clonal aging is due, in large part, to a progressive accumulation of DNA damage; and that rejuvenation is due to the repair of this damage in the micronucleus during meiosis. Meiosis appears to be an adaptation for DNA repair and rejuvenation in P. tetraurelia. In P. tetraurelia, CtlP protein is a key factor needed for the completion of meiosis during sexual reproduction and recovery of viable sexual progeny. The CtlP and Mre11 nuclease complex are essential for accurate processing and repair of double-strand breaks during homologous recombination.

Paramecium aurelia species complex:

Other species:

1. ^ Dobell, Clifford (1932). Antony van Leeuwenhoek and his "Little Animals" (1960 ed.). New York: Dover. pp. 164-165. ISBN 978-0-486-60594-4.

2. ^ Joblot, Louis (1718). Description et usages de Plusieurs Nouveaux Microscopes, tant simple que composez (in French). Vol. 2. Paris: Jacques Collombat. p. 79.

3. ^ Woodruff, Lorande Loss (September 1921). "The structure, life history, and intrageneric relationships of Paramecium calkinsi, sp. nov". The Biological Bulletin. 41 (3): 171-180. doi:10.2307/1536748. JSTOR 1536748.

4. ^ Curds, Colin R.; Gates, Michael; Roberts, David McL. (1983). British and other freshwater ciliated protozoa. Vol. 2. Cambridge University Press. p. 126.

5. ^ Esteban, Genoveva F.; Fenchel, Tom; Finlay, Bland J. (2010). "Mixotrophy in Ciliates". Protist. 161 (5): 621-641. doi:10.1016/j.protis.2010.08.002. PMID 20970377.

6. ^ Blake, John R.; Sleigh, Michael A. (February 1974). "Mechanics of ciliary locomotion". Biological Reviews. 49 (1): 85-125. doi:10.1111/j.1469-185x.1974.tb01299.x. PMID 4206625. S2CID 41907168.

7. ^ Ogura, A., and K. Takahashi. "Artificial deciliation causes loss of calcium-dependent responses in Paramecium" (1976): 170-172.

8. ^ Katsu-Kimura, Yumiko; et al. (2009). "Substantial energy expenditure for locomotion in ciliates verified by means of simultaneous measurement of oxygen consumption rate and swimming speed". Journal of Experimental Biology. 212 (12): 1819-1824. doi:10.1242/jeb.028894. PMID 19482999.

9. ^ Osterman, Natan; Vilfan, Andrej (September 20, 2011). "Finding the ciliary beating pattern with optimal efficiency" (PDF). Proceedings of the National Academy of Sciences. 108 (38): 15727-15732. arXiv:. Bibcode:2011PNAS..10815727O. doi:10.1073/pnas.1107889108. PMC . PMID 21896741.

10. ^ Berger, Jacques (1980). "Feeding Behaviour of Didinium nasutum on Paramecium bursaria with Normal or Apochlorotic Zoochlorellae". Journal of General Microbiology. 118 (2): 397-404. doi:10.1099/00221287-118-2-397.

11. ^ Kreutz, Martin; Stoeck, Thorsten; Foissner, Wilhelm (2012). "Morphological and Molecular Characterization of Paramecium (Viridoparamecium nov. subgen.) chlorelligerum Kahl (Ciliophora)". Journal of Eukaryotic Microbiology. 59 (6): 548-563. doi:10.1111/j.1550-7408.2012.00638.x. PMC . PMID 22827482.

12. ^ Aury, Jean-Marc; Jaillon, Oliver; Wincker, Patrick; et al. (November 2006). "Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia". . 444 (7116): 171-8. Bibcode:2006Natur.444..171A. doi:10.1038/nature05230. PMID 17086204.

13. ^ Lekomtsev, Sergey; Kolosov, Petr; Bidou, Laure; Frolova, Ludmila; Rousset, Jean-Pierre; Kisselev, Lev (June 26, 2007). "Different modes of stop codon restriction by the Stylonychia and Paramecium eRF1 translation termination factors". Proceedings of the National Academy of Sciences of the United States of America. 104 (26): 10824-9. Bibcode:2007PNAS..10410824L. doi:10.1073/pnas.0703887104. PMC . PMID 17573528.

14. ^ Armus, Harvard L.; Montgomery, Amber R.; Jellison, Jenny L. (Fall 2006). "Discrimination Learning in Paramecia (P. caudatum)". The Psychological Record. 56 (4): 489-498. doi:10.1007/BF03396029. S2CID 142785414.

15. ^ Ginsburg, Simona; Jablonka, Eva (2009). "Epigenetic learning in non-neural organisms". Journal of Biosciences. 34 (4): 633-646. doi:10.1007/s12038-009-0081-8. PMID 19920348. S2CID 15507569.

16. ^ Raikov, I.B (1972). "Nuclear phenomena during conjugation and autogamy in ciliates". Research in Protozoology. 4: 149.

17. ^ Berger, James D. (October 1986). "Autogamy in Paramecium cell cycle stage-specific commitment to meiosis". Experimental Cell Research. 166 (2): 475-485. doi:10.1016/0014-4827(86)90492-1. PMID 3743667.

18. ^ Raikov, I.B (1972). "Nuclear phenomena during conjugation and autogamy in ciliates". Research in Protozoology. 4: 151, 240.

19. ^ Aufderheide, Karl J. (1986). "Clonal aging in Paramecium tetraurelia. II. Evidence of functional changes in the macronucleus with age". Mechanisms of Ageing and Development. 37 (3): 265-279. doi:10.1016/0047-6374(86)90044-8. PMID 3553762. S2CID 28320562.

20. ^ Smith-Sonneborn, J. (1979). "DNA repair and longevity assurance in Paramecium tetraurelia". . 203 (4385): 1115-1117. Bibcode:1979Sci...203.1115S. doi:10.1126/science.424739. PMID 424739.

21. ^ Holmes, George E.; Holmes, Norreen R. (July 1986). "Accumulation of DNA damages in aging Paramecium tetraurelia". Molecular and General Genetics. 204 (1): 108-114. doi:10.1007/bf00330196. PMID 3091993. S2CID 11992591.

22. ^ Gilley, David; Blackburn, Elizabeth H. (1994). "Lack of telomere shortening during senescence in Paramecium" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 91 (5): 1955-1958. Bibcode:1994PNAS...91.1955G. doi:10.1073/pnas.91.5.1955. PMC . PMID 8127914.

23. ^ Bernstein, H; Bernstein, C (1991). Aging, Sex, and DNA Repair. San Diego: Academic Press. pp. 153-156. ISBN 978-0120928606.

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Paramecium ( PARR-ə-MEE-sh(ee-)əm , -⁠see-əm ; also spelled Paramoecium ) is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. Paramecia are widespread in freshwater, brackish, and marine environments and are often very abundant in stagnant basins and ponds.

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Euglena, genus of more than 1,000 species of single-celled flagellated (i.e., having a whiplike appendage) microorganisms that feature both plant and animal characteristics. Found worldwide, Euglena live in fresh and brackish water rich in organic matter and can also be found in moist soils. As photosynthetic protists, Euglena have a taxonomy that is somewhat contentious, and the genus is usually placed in the phylum Euglenozoa. Previous classifications placed the genus in the algal phylum Euglenophyta.

Euglena are characterized by an elongated cell (15-500 micrometres [1 micrometre = 10 −6 metre], or 0.0006-0.02 inch) with one nucleus, numerous chloroplasts (cell organelles that contain chlorophyll and are the site of photosynthesis), a contractile vacuole (organelle that regulates the cytoplasm), an eyespot, and one or two flagella. Certain species (e.g., E. rubra) appear red in sunlight because they contain a large amount of carotenoid pigments. Unlike plant cells, Euglena lack a rigid cellulose wall and have a flexible pellicle (envelope) that allows them to change shape. Though they are photosynthetic, most species can also feed heterotrophically (on other organisms) and absorb food directly through the cell surface via phagocytosis (in which the cell membrane entraps food particles in a vacuole for digestion). Food is often stored as a specialized complex carbohydrate known as paramylon, which enables the organisms to survive in low-light conditions. Euglena reproduce asexually by means of longitudinal cell division, in which they divide down their length, and several species produce dormant cysts that can withstand drying.

Some species, especially E. viridis and E. sanguinea, can develop large toxic populations of green or red " blooms" in ponds or lakes with high nitrogen content. E. gracilis is common in laboratory demonstrations, and a number of species are used to study cell growth and metabolism in various environmental conditions.

The Editors of Encyclopaedia Britannica Melissa Petruzzello.

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Euglena | Definition, Diagram, Movement, Classification, & Facts

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Euglena, genus of more than 1,000 species of single-celled flagellated microorganisms that feature both plant and animal characteristics. They are photosynthetic, and most species can also feed heterotrophically. Learn more about Euglena with this article.

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Euglena is a genus of single-celled flagellate eukaryotes. It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 800 species. Species of Euglena are found in fresh and salt waters.

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Stentor, genus of trumpet-shaped, contractile, uniformly ciliated protozoans of the order Heterotrichida. They are found in fresh water, either free-swimming or attached to submerged vegetation. Stentor assumes an oval or pear shape while swimming. At its larger end, Stentor has multiple ciliary membranelles spiraling around the region that leads to the mouth opening. It uses these cilia to sweep food particles into its cytostome. The species S. coeruleus is large (sometimes up to 2 mm [0.08 inch] long) and is predominantly blue from a blue pigment, stentorin, found in its ectoplasm. Stentor is remarkable for its regenerative powers; a small fragment less than one-hundredth of the volume of an adult can grow back into a complete organism. This capability has made Stentor a favourite subject for studies of regeneration in protozoans.

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Stentor, genus of trumpet-shaped, contractile, uniformly ciliated protozoans of the order Heterotrichida. They are found in fresh water, either free-swimming or attached to submerged vegetation. Stentor assumes an oval or pear shape while swimming. At its larger end, Stentor has multiple ciliary membranelles spiraling around the region that leads to the mouth opening.

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Stentor is a genus of trumpet-shaped ciliates found primarily in stagnant fresh water. There are 22 known species of Stentor but there are most likely more that have yet to be discovered. Reaching a length of up to two millimeters, Stentor are amongst the largest known unicellular microorganisms. Although capable of swimming, it prefers to attach to a substrate using its holdfast (anchor) and extend to great lengths and then retract its body. Its regenerative properties and large size make it an ideal model organism for scientific inquiry.
Studying microorganisms such as Stentor for their amazing regenerative properties has helped shape modern medicine. Before observing these magnificent microorganisms, it is recommended to learn about them first so you can fully appreciate them. This article intends to help you gain a deeper understanding of the Stentor's habitats, structures, and behaviors.

What is the Structure or Anatomy of Stentor?

Stentor are unicellular, meaning that they consist of only one large cell that is capable of carrying out all of the functions needed to sustain life. This large cell is capable of eating, digesting, excreting, breathing, and even reproducing all by itself. To understand how this is even possible, we must first understand its anatomy.

The organism relies heavily on hair-like structures called cilia for many of its critical functions. Cilia are found all over the body and provide two main functions which include the ability to move in unison to help the organism swim through water. It also helps move in a circular, and vibratory manner to pull water towards the mouth area. This helps attract food towards its gullet where bacteria and other food sources are filtered and ingested.

The many different variations of pigmentation seen in the Stentor are mainly attributed to the different types of algae ingested. They typically don't eat algae for food, but instead, work together in symbiosis. The symbiotic relationship benefits the algae with safety and the Stentor with a food source. The algae also feed off of waste excrement from the Stentor and utilizes it for its own photosynthetic processes. This in turn produces nutrients for the Stentor.

The Stentor's use of a contractile vacuole is another key feature. As the Stentor lives only in freshwater environments, the salinity content within is higher than that of its surrounding environment. This requires osmosis to take place in order to keep an equilibrium. Once the vacuole fills with water, it contracts and squeezes the water back out of the cell which keeps it balanced.

Let's take a look at the Stentor's physical structure next:

Oral Cilia: Located at the anterior end of the cell, the oral cilia consistently pulsate which creates a vortex of water that pulls food towards its buccal cavity. The cilia further aid in filtering out and grabbing food sources such as bacteria as they pass by. Cilia are hair-like and protrusive organelles that are either motile or non-motile. Non-motile cilia serve primarily as sensory organelle whereas motile cilia can help the body of the cell move.

Contractile Vacuole: The contractile vacuole is a specialized organelle that is found mainly in protists like the Stentor. This structure was touched on briefly above. A contractile vacuole can also help an organism move. Expelling water can act as a jet to propel an organism through the water. In the Stentor, it can be located just beneath the cell's membrane. The scar-like features seen on the Stentor are actually vacuole pores.

Buccal Cavity: A buccal cavity is a fancy way to say an organism's mouth. It refers to the cheek cavity structure of an organism. The buccal cavity's main function is to store and pass food along to the digestive system. The Stentor has an exceptionally large and prominent buccal cavity at the bell of its trumpet.

Macronucleus: A macronucleus is a larger type of nucleus that is found mainly in ciliates. It stretches the entire length of the Stentor's body and looks like a long strand of beads within the cell body. Macronuclei are polypoid and do not use mitosis to divide. The organelle is responsible for non-reproductive functions of the organism such as its metabolism. When conjugation occurs, the macronucleus actually disintegrates and a new one is formed. The macronucleus is somewhat of a mystery as it contains thousands of chromosomes but is incapable of partitioning itself during division.

Cortical Stripes: The visible stripes on the Stentor are fibers that contain pigmented granules. When the wide stripes intersect with the narrow stripes, a feature called the locus of stripe contrast is formed. The color of the pigment depends on the kind of algae that the Stentor is eating or living symbiotically with.

Holdfast: The holdfast, or the anchor, is the structure that allows the Stentor to attach to its substrate of choice. The anchor is strong enough to hold up the Stentor's large body but too weak to withstand any significant flows of water. This is why Stentor are mainly found in stagnant or low-flow bodies of water.

How are Stentor Classified?

Stentor are classified as a Genus. Below is the full classification for stentor:

Domain: Eukaryota - This Domain consists of the majority of the observable life that you're familiar with, including plants, animals, fungi, algae, and protists. Each organism within this Domain possesses eukaryotic cells and a genome compartmentalized within a nucleus.

Kingdom: Protista - Protista are just one of the five Kingdoms. Stentors are more commonly classified amongst an infrakingdom called the Alveolata and a subkingdom called the SAR supergroup.

Subkingdom: SAR - The SAR supergroup is an acronym for a clade of Stramenopiles, Alveolata, and Rhizaria.

Infrakingdom: Alveolata - This is a major clade of alveolates which represent a group of protists with body cavities. It's an exclusive grouping with only two phyla beneath it. Defining characteristics of this clade include outer alveoli which are flattened vesicles that are layered on top of one another just beneath the membrane. It creates supports and also forms a thin skin that can form an armor-like plate. Ciliates are among the most common Alveolata.

Phylum: Cilophora - (phylum of the ciliates) is a group of protozoans known best for their hair-like organelles known as cilia. It's a strikingly similar structure to flagella but are generally shorter and occur in greater numbers.

Class: Heterotrichea - A class of ciliates that have a distinctive membrane surrounding its mouth which may be used in either locomotion or feeding. The rest of the body is typically lined with a shorter cilia. Many of the organisms within this class are contractile and spend most of their time compressed or in a conical shape. Heterotrichea contains some of the largest protozoa, including Stentor and Spirostomum. Many species within this class are pigmented such as the blue Stentor coeruleus and the red Blepharisma.

Order: Heterotrichida - The Order heterotrichida is best known for its large to very large-sized protists. Not only are the protists large, but they are highly contractile. The order is widely distributed, and the organisms are mostly free-living. Dense rows of cilia are present with undulating membranes.

Family: Stentoridae - This family is recognized for its large size and ability to move freely. All Stentoridae have a trumpet-shaped buccal cavity region and have the ability to elongate and retract. They can be symbiotic by nature and are oftentimes pigmented.

Genus: Stentor - The Stentor are horn-shaped organisms with a ring of cilia around its bell. They prefer to filter feed and spend their time attached to a substrate but do have the ability to swim thanks to their cilia. They are amongst the largest single-celled organisms on the planet. There are currently over 22 described species of Stentor.

What are the Most Common Types of Stentor?

There are only 22 known species of Stentor. Of those 22, the most prevalent species and their characteristics are listed below:

Stentor amethystinus: Growing up to 1 millimeter in length, this species is found commonly in freshwater ponds and lakes. They live symbiotically with algae which provide food for the species. The Stentor that lines the algae adds a layer of protection in turn. Unlike many of the other species of Stentor, this species gives off a red or violet color due to a chemical called amethystin.

Stentor coeruleus: Characterized by its giant size, this species can grow up to two millimeters when fully extended. It is known for possessing the largest 'trumpet' out of all species. A macronucelus within the Stentor is organized in a string of beads that are blue or bluish-green in color. The Stentor has the ability to contract down into a ball. It can also swim while fully extended or in a ball shape. This is one of the most commonly studied Stentor thanks to its regenerative abilities. When cut in half, it can regenerate so effectively that you cannot recognize where the incision was made.

Stentor muelleri: This species is exceptionally long and can reach up to 3 millimeters in length. It's found mainly in freshwater bodies but sometimes estuaries as well.

Stentor roselii: A free-living version of the Stentor, this species is one of the most common and abundant Stentor in the world. It's a colorless species without any pigmentation in its cortex. Cilia are organized in 40 to 80 longitudinal rows on the body.

What do Stentor Eat?

Thanks to the large size of the Stentor, it can feed freely on just about any organism smaller than itself. Its large trumpet-shaped mouth allows for it to fit nearly all organisms smaller than it within its mouth. Stentor are so large that they have been observed eating multicellular organisms such as rotifers and water fleas.

The Stentor uses its cilia around its mouth to capture food and filter it. Water that enters through the mouth passes through and undergoes osmosis and exits back out the vacuole. If the Stentor cannot find food to its liking, then it is perfectly capable of detaching and moving to a new location to filter feed from. Although Stentor have the ability to eat multicellular organisms thanks to their size, they feed mainly on bacteria and other protozoans. However, Stentor have been known to be cannibalistic and eat their own species, but this has never been document on film.

Where do Stentor Live?

The habitat of the Stentor is mainly within freshwater bodies like lakes, ponds, puddles, and slow-moving creeks. They tend to avoid flowing water such as streams and turbulent areas because of their odd shape. Flowing water easily washes away the top-heavy and trumpet-shaped organism. Still or stagnant water is ideal for the Stentor to live within.

Since their diet consists mainly of bacteria, it makes sense that the Stentor prefers to live in stagnant water where bacteria are feeding on decomposing organic matter such as leaf litter. Even if Stentor could hold on and not be swept away by moving water, it's unlikely that they would choose to stay living in moving water. Flowing water is troublesome for bacteria because decomposing organic matter washes away too quickly.

Regardless of flowing water, the Stentor will always choose to live closest to its beloved food source. Stentor are also commonly found near light sources which means that they are found in shallow water. This is due to their symbiotic relationship with algae. Since green algae are photosynthetic, they need to be near a light source to create energy for themselves.

How do Stentor Reproduce?

Stentor have two means of reproduction, conjugation, and binary fission. Stentor prefer to undergo binary fission unless the conditions are unfavorable. As discussed previously, the Stentor has a macronucleus which although holds genetic information, is incapable of aiding in reproduction. Instead, the Stentor relies on its micronucleus.

When two Stentor cross paths, the micronucleus replicates itself and the genetic information is exchanged. The exchanged information reorganizes and becomes a new macronuclei. Throughout the course of its life, the Stentor undergoes asexual reproduction multiple times before it is ready to sexually reproduce again.

Conjugation

Conjugation is a complex form of isogamy which is a form of sexual reproduction that is unique to unicellular organisms. As a unicellular organism, each and every organism is virtually identical in structure meaning that they generally cannot be classified as male or female. Instead of being referred to as male or female, they express + or - strains of DNA. Regardless, fertilization takes place and gametes of two separate organisms combine to form a zygote. It's theorized that isogamy is ancestral to sexual reproduction as we know it today.

Binary Fission

Fission refers to the division of a single organism into two or more equal organisms that resemble or are identical to the parent. This is the preferred and most common form of reproduction amongst the Stentor. During this process, the DNA replicates within a micronucleus since the Stentor's macronucleus does not assist in division.

The replicates scatter themselves throughout the cell's membrane and begin to tear apart. As the membrane tears apart, half of the genetic material that is replicated and half of the genetic material that is original is separated. In this process, new cells are genetically identical.

How to Observe Stentor Under the Microscope

Stentor are massive microorganisms and their distinctive trumpet shape makes them very easy to spot. Stentor tend to be found near large accumulations of algae. So if you are looking for Stentor make sure when you take a sample there is plenty of algae. Larger stentor can even be seen without a microscope especially when they are fully elongated.

Stentor tend to move very slowly but most of the time they are anchored to microscopic debris, so it is very easy to use high magnifications to observe the minute details of these magnificent microorganisms. Aside from being very easy to observe their cyan color makes them one of the most beautiful microorganisms on the planet in my humble opinion.

When Were Stentor First Discovered?

The name of the Stentor comes from its trumpet shape and the herald in Greek mythology known for possessing a booming voice. The Stentor was first observed and documented in 1744 by Abraham Trembley. Abraham Trembley was a Genevan naturalist known for his work as it related to hydra. Trembley is credited as the father of zoology. Some go as far as calling him the father of biology.

Trembley thought he had discovered a new species in the hydra, but it was in fact first written about by Leeuwenhoek in 1702. In 1744, he published his groundbreaking book called Memoires pour server a l'histoire d'un genre de polypes d'eau douce. The book included the most detailed drawings and explanations of the hydra.

Within this groundbreaking novel was an excerpt about a large, trumpet-shaped ciliate that was thought to have been a hydra at the time. Trembley was unwittingly describing the Stentor and mistakenly grouping it with the hydra. It wasn't until 1815 that the Stentor was revisited by German naturalist Lorenz Oken.

Lorenz Oken was a botanist, biologist, and ornithologist. He specialized in natural history and medicine. Oken established himself as the leader of the "Naturphilosophie' movement in Germany when he began his series of work with a book titled Grundriss der Naturphilosophie, der Theorie der Sinne, mit der darauf gegrundeten Classificaton der Thiere in 1802. Oken was particularly fascinated by Stentor thanks to his background in medicine.

In fact, Oken was a professor of medical sciences at the University of Jena for a short while. Stentor, like hydra, have amazing regenerative properties that fascinated Oken. He recognized that Stentor should not be classified as hydra based on sensory organs and helped reclassify them and push them into mainstream science.

References

1. https://owlcation.com/stem/Stentor-A-Trumpet-Shaped-Organism-With-Interesting-Behaviour

2. https://study.com/academy/lesson/stentor-protist-reproduction-anatomy-habitat.html

3. https://www.canadiannaturephotographer.com/stentor.html

4. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/ciliophora

5. http://species-identification.org/species.php?species_group=zsao&id=213&menuentry=groepen

6. http://species-identification.org/species.php?species_group=zsao&id=217&menuentry=groepen

7. https://www.researchgate.net/figure/A-descriptive-diagram-of-Stentor-coeruleus-All-of-the-features-shown-are-on-the-cell_fig3_233929863

8. http://www.madsci.org/posts/archives/2000-11/975558285.Cb.r.html

9. https://www.cell.com/current-biology/pdf/S0960-9822(14)00760-X.pdf

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Stentor: Structure, Classification, and Characteristics | Microscope Clarity

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Stentor is a genus of trumpet-shaped ciliates found primarily in stagnant fresh water. There are 22 known species of Stentor but there are most likely more that have yet to be discovered.

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Daphnia

Scientific classification

Order:

Cladocera

Family:

Daphniidae

Genus:

Daphnia
Müller, 1785

Subgenera

Subgenus Daphnia

Subgenus Hyalodaphnia

Subgenus Ctenodaphnia

Daphnia is a genus of small, aquatic, mostly freshwater crustaceans, generally between .2 and 5 mm (.008 to .2 inches) in length, belonging to the Daphniidae family of the Cladocera order, and characterized by a single compound eye, two doubly branched antennae, and a generally translucent carapace. Daphnia or daphnids are commonly called water fleas because of their jerky or jumping swimming style (although fleas are insects and thus these two groups are only very distantly related as being arthropods).

However, the common name water flea also is applied to other animals, including members of the Cladocera order in general, as well as the copepod genera Cyclops and Diaptomus.

Daphnids, which are mostly planktonic, live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams, and rivers. There are no known marine representatives of the Daphnia genus, and only about one percent of Cladocerans are found outside of freshwater environments, mostly in brackish water.

Like other taxa, daphnia exhibit a bi-level functionality, advancing not only their own survival, reproduction, and development, but also playing a valuable role in the ecosystem and for humans. Ecologically, daphnia are important components of freshwater food chains, consuming algae and other small organisms, and in turn being prey for small fish and other carnivorous aquatic animals. For humans, daphnia not only add to the wonder of nature, but also are a valuable species for research and as an indicator species. Their translucent carapace particularly makes them excellent subjects under the microscope.

Description

Cladocera and Crustacea

Daphnia are crustaceans (subphylum Crustacea), a group of arthropods that includes the familiar crabs, lobsters, shrimps, barnacles, copepods, krill, and crayfish. Crustaceans are characterized by having branched (biramous) appendages, an exoskeleton made up of chitin and calcium, two pairs of antennae that extend in front of the mouth, and paired appendages that act like jaws, with three pairs of biting mouthparts. They share with other arthropods the possession of a segmented body, a pair of jointed appendages on each segment, and a hard exoskeleton that must be periodically shed for growth. Most species of crustaceans are marine, but there are many freshwater forms, such as crayfish and Daphnia, and some terrestrial forms.

The order to which daphnia belong, Cladocera, is comprised of free-swimming organisms, and most orientate themselves with dorsal side up. They have a two-valved carapace, generally covering most of the body except the appendages. The head is typically separated from the body by a deep indentation, but also may not be separated. It projects forward as a beak or rostrum. On the forehead is an unpaired compound eye, a result of two fused eyes, and, in most species, a simple naupliar eye (an organ retained from the "naupliar" larval stage). The number of ommatidia that make up the compound eye varies from species to species according to their food preferences. The plankton-filtering Daphnia has an eye of only 22 ommatidia, while the carnivorous Evadne and Leptodora have 80 and 300, respectively.

In Cladocera, the first pair of antennae that contains sensory organs is quite small and is attached to the rostrum. The second pair, however, is disproportionably large compared to the body. Each of the second pair of antennae has two branches, and both branches bear long, feathery bristles. The second pair of antennae is the primary organ of both locomotion and catching food in water fleas.

On the lower side of the head is the mouth, surrounded by the upper lip in front, the mandibles at the sides, and the maxillae (jaws) at the back. The thorax of water fleas is very short and consists of four to six segments.

In Daphnia, the division of the body into segments is nearly invisible. The head is fused, and is generally bent down toward the body with a visible notch separating the two. In most species, the rest of the body is covered by a carapace, with a ventral gap in which the five or six pairs of legs lie. The most prominent features are the compound eye, the second pair of antennae, and a pair of abdominal setae.

In many species, the carapace is translucent or nearly so. The heart is at the top of the back, just behind the head, and the average heart rate of daphnids is approximately 180 beats per minute under normal conditions.

Swimming is powered mainly by the second set of antennae, which are larger in size than the first set. The action of this second set of antennae is responsible for the jumping motion.

The lifespan of a Daphnia does not exceed one year and is largely temperature dependent. For example, individual organisms can live up to 108 days at 3 °C while some organisms live for only 29 days at 28°C. A clear exception to this trend is during the winter time in which harsh conditions limit the population and in which females have been recorded to live for over six months. These females generally grow at a slower rate but in the end are larger than ones under normal conditions.

Feeding behavior

A few Daphnia prey on tiny crustaceans and rotifers, but most are filter feeders, ingesting mainly unicellular algae and various sorts of organic detritus including protists and bacteria. They also eat forms of yeast, but mostly in laboratories or controlled environments. Daphnia can be kept easily on a diet of yeast.

Beating of the legs produces a constant current through the carapace, which brings such material into the digestive tract. The trapped food particles are formed into a food bolus, which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage.

The first and second pairs of legs are used in the organisms' filter feeding, ensuring that particles too large to handle are kept out while the other sets of legs create the stream of water rushing into the organism.

Life cycle and reproduction

Under favorable environmental conditions, Daphnia reproduce parthenogenetically, usually in the spring until the end of the summer.

One or more juvenile animals are nurtured in the brood pouch inside the carapace. The newly hatched Daphnia must molt several times before they are fully grown into an adult usually after about two weeks. The young are small copies of the adult; there are no true nymphal stages.

Fully mature females are able to produce a new brood of young about every ten days under ideal conditions. The reproduction process continues while the environmental conditions continue to support their growth.

When winter approaches, or in drought conditions, or at times of other harsh environmental conditions, production of new female generations ceases and parthenogenic males are produced. However, even in harsh environmental conditions, males may make up considerably less than half the population; in some species males are unknown. Males tend to be much smaller in size than females, and are also distinguished by larger antennules (Clare 2002). They typically possess a specialized abdominal appendage, which is used in mating to grasp a female from behind and prise open her carapace and insert a spermatheca, and thus fertilize the eggs. These fertilized eggs are termed winter eggs and are provided with extra shell layer called ephippium. The extra layer preserves and protects the egg inside from harsh environmental conditions until the more favorable times, such as spring, when the reproductive cycle is able to take place once again.

In addition to the production of eggs capable of overwintering, this switch to sexual reproduction has also been proposed to allow greater offspring variation (through genetic recombination), which may be useful in varied or unpredictable conditions.

Importance

Ecologically, daphnia are important components of freshwater food chains, consuming algae and other small organisms, and in turn being prey for small fish and other carnivorous aquatic animals, such as the immature aquatic stages of dragonflies and damselflies.

For humans, daphnia also make model organisms for biological study. The translucent carapace makes them excellent subjects for the microscope as one can observe the beating heart. Even under relatively low power, it is possible to observe the feeding mechanism working, watch immature young moving in the brood-pouch, observe the eye being moved by the ciliary muscles, and even watch blood corpuscles being pumped round the circulatory system by the simple heart. Daphnids, like many animals, are prone to alcohol intoxication, and make excellent subjects for studying the effects of the depressant on the nervous system-due to the translucent exoskeleton, and the visibly altered heart rate. They are tolerant of being observed, live under a cover slip and appear to suffer no harm when returned to open water. This experiment can also be done using caffeine, nicotine, or adrenaline and observing an increase in heart rate.

Sometimes Daphnia may be used in certain environments to test the effects of toxins on an ecosystem. This makes Daphnia an indicator species, particularly useful for that purpose because of its short lifespan and reproductive capabilities.

The populations of several water flea species are considered threatened. The following daphnids are listed as vulnerable by IUCN: Daphnia nivalis, Daphnia coronata, Daphnia occidentalis, and Daphnia jollyi.

References

External links

All links retrieved June 25, 2022.

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Daphnia Scientific classification Order: Cladocera Family: Daphniidae Genus: Daphnia Müller, 1785 Subgenera Subgenus Daphnia Subgenus Hyalodaphnia Subgenus Ctenodaphnia Daphnia is a genus of small, aquatic, mostly freshwater crustaceans, generally between .2 and 5 mm (.008 to .2 inches) in length, belonging to the Daphniidae family of the Cladocera order, and characterized by a single compound eye, two doubly branched antennae, and a generally translucent carapace.

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Paramecium or Paramoecium is a genus of unicellular ciliated protozoa. They are characterised by the presence of thousands of cilia covering their body. They are found in freshwater, marine and brackish water. They are also found attached to the surface. Reproduction is primarily through asexual means (binary fission). They are slipper-shaped and also exhibit conjugation. They are easy to cultivate and widely used to study biological processes.

Table of Content

Paramecium Classification

Paramecium is unicellular and eukaryotic, so they are kept in the kingdom Protista. They are ciliated protozoan and come under phylum Ciliophora.

The common species of Paramecium include:
Paramecium aurelia Paramecium caudatum Paramecium woodruffi Paramecium trichium
Features

The cell size varies from 50 µ to 300 µ. The cell is ovoid, slipper or cigar-shaped

The cellular cytoplasm is enclosed in a pellicle. Pellicle consists of an outer plasma membrane, inner epiplasm and a layer of alveoli, present in between both the layers. The pellicle is elastic and gives the cell its definite but changeable shape

Cilia project from the depressions in the pellicle and cover the entire body surface. They are used for locomotion and taking nutrient-rich water inside the gullet

Protoplasm is divided into outer ectoplasm and inner endoplasm, which is granular

Trichocysts are present and embedded in the ectoplasm. They are a defensive organ

The endoplasmic granules reserve food. Some of the granules are secretory or excretory

Paramecia contain at least two nuclei, micronuclei (one or more) and one macronucleus. Micronuclei have diploid chromosomes and take part in the reproduction. Macronuclei regulate all vital metabolic activities and growth. The macronucleus has multiple copies of the genome, i.e. polyploid

Contractile vacuoles are present and their number varies from species to species. They are required for osmoregulation and expel the additional absorbed water

At the midpoint, there is an oral groove on the ventral side known as the vestibule. Food is drawn inside the cell due to coordinated movement of cilia

The oral groove opens in the mouth known as cytostome and to the gullet or pharynx

There are numerous food vacuoles present for digesting food

There is an anal pore present on the ventral surface in the posterior half of the cell known as cytoproct or cytopyge, which helps in egesting undigested food

Paramecium caudatum is the most common and well known species of the genera.

Paramecium Locomotion

The coordinated movement of thousands of cilia propels paramecium. Paramecium can rotate around its axis and move in the reverse direction on encountering an obstacle.

Paramecium Nutrition

They are mostly heterotrophic. They feed on bacteria, algae, yeast and other microorganisms. They are holozoic. The food-laden water is drawn inside by the movement of cilia and it goes to the cytostome and to the gullet (cytopharynx).

The food gets loaded at the posterior end of cytopharynx. It gets surrounded by vacuoles, pinches off and circulates in the endoplasm. The food is acted upon by digestive enzymes present in the food vacuoles.

The undigested residue is egested through the temporary anal pore (cytopyge).

Some of the Paramecium species, e.g. Paramecium bursaria, etc. form a symbiotic relationship with green algae. Algae are present as an endosymbiont and provide food to paramecium by photosynthesis, in turn, the algae get a safe and protective habitat.

Paramecium may have intracellular bacteria known as kappa particles. Paramecium with kappa particles has the ability to kill other strains of paramecium.

Paramecium Reproduction

Asexual Reproduction in paramecium is by binary fission. The mature cell divides into two cells and each grows rapidly and develops into a new organism. Under favourable conditions, Paramecium multiplies rapidly up to three times a day. Binary fission divides a cell transversely and followed by mitotic division in the micronucleus. Macronucleus divides amitotically. The gullet also divides into two halves.

Although the favoured mode of reproduction in Paramecium is mostly asexual, they reproduce sexually too, when there is a scarcity of food.

Sexual reproduction in Paramecium is by various methods.

In conjugation, two complementary paramecia (syngen) come together and there is a transfer of genetic material. An individual has to multiply asexually 50 times before reproducing by conjugation.

In the process of conjugation, the conjugation bridge is formed and united paramecia are known as conjugants. Macronuclei of both the cells disappear. The micronucleus of each conjugant forms 4 haploid nuclei by meiosis. Three of the nuclei degenerate. The haploid nuclei of each conjugant then fuse together to form diploid micronuclei and cross-fertilization takes place. The conjugants separate to form exconjugants. They are identical, but different from the earlier cells. Each exconjugate undergoes further division and forms 4 daughter Paramecia. Micronuclei form a new macronucleus.

Paramecium also shows autogamy i.e. self-fertilization. A new macronucleus is produced, which increases their vitality and rejuvenates them.

Cytogamy is less frequent. In cytogamy, two paramecia come in contact but there is no nuclear exchange. Paramecium rejuvenates and a new macronucleus is formed.

A Paramecia undergoes ageing and dies after 100-200 cycles of fission if they do not undergo conjugation. The macronucleus is responsible for clonal ageing. It is due to the DNA damage.

Learn about other protists and similar concepts related to NEET only at BYJU'S.
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Paramecium or Paramoecium is a genus of unicellular ciliated protozoa. They are characterised by the presence of thousands of cilia covering their body. They are found in freshwater, marine and brackish water. They are also found attached to the surface. Reproduction is primarily through asexual means (binary fission).

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From Wikipedia, the free encyclopedia

Clockwise from top right: Amoeba proteus, Actinophrys sol, Acanthamoeba sp., Nuclearia thermophila., Euglypha acanthophora, neutrophil ingesting bacteria.

An amoeba (; less commonly spelled ameba or amœba; PL : am(o)ebas or am(o)ebae ),[1] often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods.[2] Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, and animals.[3][4][5][6][7]

Microbiologists often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits amoeboid movement.[8][9]

In older classification systems, most amoebae were placed in the class or subphylum Sarcodina, a grouping of single-celled organisms that possess pseudopods or move by protoplasmic flow. However, molecular phylogenetic studies have shown that Sarcodina is not a monophyletic group whose members share common descent. Consequently, amoeboid organisms are no longer classified together in one group.[10]

The best known amoeboid protists are Chaos carolinense and Amoeba proteus, both of which have been widely cultivated and studied in classrooms and laboratories.[11][12] Other well known species include the so-called "brain-eating amoeba" Naegleria fowleri, the intestinal parasite Entamoeba histolytica, which causes amoebic dysentery, and the multicellular "social amoeba" or slime mould Dictyostelium discoideum.

Shape, movement and nutrition

The forms of pseudopodia, from left: polypodial and lobose; monopodial and lobose; filose; conical; reticulose; tapering actinopods; non-tapering actinopods

Amoeba do not have cell walls, which allows for free movement. Amoeba move and feed by using pseudopods, which are bulges of cytoplasm formed by the coordinated action of actin microfilaments pushing out the plasma membrane that surrounds the cell.[13] The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another. Amoebozoan species, such as those in the genus Amoeba, typically have bulbous (lobose) pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as Euglypha and Gromia, have slender, thread-like (filose) pseudopods. Foraminifera emit fine, branching pseudopods that merge with one another to form net-like (reticulose) structures. Some groups, such as the Radiolaria and Heliozoa, have stiff, needle-like, radiating axopodia (actinopoda) supported from within by bundles of microtubules.[3][14]

Free-living amoebae may be " testate" (enclosed within a hard shell), or "naked" (also known as gymnamoebae, lacking any hard covering). The shells of testate amoebae may be composed of various substances, including calcium, silica, chitin, or agglutinations of found materials like small grains of sand and the frustules of diatoms.[15]

To regulate osmotic pressure, most freshwater amoebae have a contractile vacuole which expels excess water from the cell.[16] This organelle is necessary because freshwater has a lower concentration of solutes (such as salt) than the amoeba's own internal fluids ( cytosol). Because the surrounding water is hypotonic with respect to the contents of the cell, water is transferred across the amoeba's cell membrane by osmosis. Without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole because the concentration of solutes within the cell are in balance with the tonicity of the surrounding water.[17]

Amoeba phagocytosis of a bacterium

The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other protists. Some are detritivores and eat dead organic material.

Amoebae typically ingest their food by phagocytosis, extending pseudopods to encircle and engulf live prey or particles of scavenged material. Amoeboid cells do not have a mouth or cytostome, and there is no fixed place on the cell at which phagocytosis normally occurs.[18]

Some amoebae also feed by pinocytosis, imbibing dissolved nutrients through vesicles formed within the cell membrane.[19]

Foraminifera have reticulose (net-like) pseudopods, and many species are visible with the naked eye

The size of amoeboid cells and species is extremely variable. The marine amoeboid Massisteria voersi is just 2.3 to 3 micrometres in diameter,[20] within the size range of many bacteria.[21] At the other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter.[22] Most of the free-living freshwater amoebae commonly found in pond water, ditches, and lakes are microscopic, but some species, such as the so-called "giant amoebae" Pelomyxa palustris and Chaos carolinense, can be large enough to see with the naked eye.

Species or cell type

Size in micrometers

Neutrophil (white blood cell)[24]

12-15

up to 200000

Neutrophil (white blood cell) engulfing anthrax bacteria

Some multicellular organisms have amoeboid cells only in certain phases of life, or use amoeboid movements for specialized functions. In the immune system of humans and other animals, amoeboid white blood cells pursue invading organisms, such as bacteria and pathogenic protists, and engulf them by phagocytosis.[31]

Amoeboid stages also occur in the multicellular fungus-like protists, the so-called slime moulds. Both the plasmodial slime moulds, currently classified in the class Myxogastria, and the cellular slime moulds of the groups Acrasida and Dictyosteliida, live as amoebae during their feeding stage. The amoeboid cells of the former combine to form a giant multinucleate organism,[32] while the cells of the latter live separately until food runs out, at which time the amoebae aggregate to form a multicellular migrating "slug" which functions as a single organism.[8]

Other organisms may also present amoeboid cells during certain life-cycle stages, e.g., the gametes of some green algae ( Zygnematophyceae)[33] and pennate diatoms,[34] the spores (or dispersal phases) of some Mesomycetozoea,[35][36] and the sporoplasm stage of Myxozoa and of Ascetosporea.[37]

Early history and origins of Sarcodina

The first illustration of an amoeboid, from Roesel von Rosenhof's Insecten-Belustigung (1755)

Amoeba proteus

The earliest record of an amoeboid organism was produced in 1755 by August Johann Rösel von Rosenhof, who named his discovery "Der Kleine Proteus" ("the Little Proteus").[38] Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to the common species now known as Amoeba proteus.[39] The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid.[40]

In 1822, the genus Amiba (from the Greek ἀμοιβή amoibe, meaning "change") was erected by the French naturalist Bory de Saint-Vincent.[41][42] Bory's contemporary, C. G. Ehrenberg, adopted the genus in his own classification of microscopic creatures, but changed the spelling to Amoeba.[43]

In 1841, Félix Dujardin coined the term " sarcode" (from Greek σάρξ sarx, "flesh," and εἶδος eidos, "form") for the "thick, glutinous, homogeneous substance" which fills protozoan cell bodies.[44] Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells.[10] Thirty years later, the Austrian zoologist Ludwig Karl Schmarda used "sarcode" as the conceptual basis for his division Sarcodea, a phylum-level group made up of "unstable, changeable" organisms with bodies largely composed of "sarcode".[45] Later workers, including the influential taxonomist Otto Bütschli, amended this group to create the class Sarcodina,[46] a taxon that remained in wide use throughout most of the 20th century.

Within the traditional Sarcodina, amoebae were generally divided into morphological categories, on the basis of the form and structure of their pseudopods. Amoebae with pseudopods supported by regular arrays of microtubules (such as the freshwater Heliozoa and marine Radiolaria) were classified as Actinopoda; whereas those with unsupported pseudopods were classified as Rhizopoda.[47] The Rhizopods were further subdivided into lobose, filose, and reticulose amoebae, according to the morphology of their pseudopods.

Dismantling of Sarcodina

In the final decade of the 20th century, a series of molecular phylogenetic analyses confirmed that Sarcodina was not a monophyletic group. In view of these findings, the old scheme was abandoned and the amoebae of Sarcodina were dispersed among many other high-level taxonomic groups. Today, the majority of traditional sarcodines are placed in two eukaryote supergroups: Amoebozoa and Rhizaria. The rest have been distributed among the excavates, opisthokonts, and stramenopiles. Some, like the Centrohelida, have yet to be placed in any supergroup.[10][48]

Classification

Recent classification places the various amoeboid genera in the following groups:

Supergroups

Major groups and genera

Morphology

Amoebozoa

Tubulinea (formerly part of Lobosa)
Amoeba, Chaos, Hydramoeba, Metachaos, Trichamoeba, Glaeseria, Hartmannella,Polychaos, Saccamoeba, Flabellula, Gephyramoeba, Leptomyxa, Rhizamoeba, Trichosphaerium, Echinamoeba,

Discosea (formerly part of Lobosa)
Acanthamoeba, Protoacanthamoeba, Balamuthia, Discamoeba, Clydonella, Hollandella, Korotnevella (Dactylamoeba), Lingulamoeba, Mayorella, Neoparamoeba, Paramoeba, Platyamoeba, Sappinia, Thecamoeba, Unda, Vannella, Vexillifera

Conosa:
Endamoeba, Entamoeba, Filamoeba, Iodamoeba, Mastigamoeba, Mastigina, Phreatamoeba,Mastigella, Pelomyxa, Dictyostelium, Physarum

incertae sedis

Lobose pseudopods (Lobosa) are blunt, and there may be one or several on a cell, which is usually divided into a layer of clear ectoplasm surrounding more granular endoplasm.

Rhizaria

Filose pseudopods (Filosa) are narrow and tapering. The vast majority of filose amoebae, including all those that produce shells, are placed within the Cercozoa together with various flagellates that tend to have amoeboid forms. The naked filose amoebae also includes vampyrellids.

Reticulose pseudopods (Endomyxa) are cytoplasmic strands that branch and merge to form a net. They are found most notably among the Foraminifera, a large group of marine protists that generally produce multi-chambered shells. There are only a few sorts of naked reticulose amoebae, notably the gymnophryids, and their relationships are not certain.

Radiolarians are a subgroup of actinopods that are now grouped with rhizarians.

Excavata

Heterolobosea:

Vahlkampfiidae: Monopylocystis, Naegleria, Neovahlkampfia, Paratetramitus, Paravahlkampfia, Protonaegleria, Psalteriomonas, Sawyeria, Tetramitus, Vahlkampfia, Willaertia

Gruberellidae: Gruberella, Stachyamoeba

Parabasalidea: Dientamoeba, Histomonas

Other: Rosculus, Acrasis, Heteramoeba, Learamoeba, Stygamoeba, Plaesiobystra,[49] Tulamoeba[49]

Heterokonta

The heterokont chrysophyte and xanthophyte algae include some amoeboid members, the latter being poorly studied.[50]

Alveolata

Parasite with amoeboid life cycle stages.

Opisthokonta

Ungrouped /
unknown

Adelphamoeba, Astramoeba, Dinamoeba, Flagellipodium, Flamella, Gibbodiscus, Gocevia, Malamoeba, Nollandia, Oscillosignum, Paragocevia, Parvamoeba, Pernina, Pontifex, Pseudomastigamoeba, Rugipes, Striamoeba, Striolatus, Subulamoeba, Theratromyxa, Trienamoeba, Trimastigamoeba, and over 40 other genera[51]

Some of the amoeboid groups cited (e.g., part of chrysophytes, part of xanthophytes, chlorarachniophytes) were not traditionally included in Sarcodina, being classified as algae or flagellated protozoa.

Trophozoites of the pathogenic Entamoeba histolytica with ingested red blood cells

Some amoebae can infect other organisms pathogenically, causing disease:[52][53][54][55]

Amoeba have been found to harvest and grow the bacteria implicated in plague.[56] Amoebae can likewise play host to microscopic organisms that are pathogenic to people and help in spreading such microbes. Bacterial pathogens (for example, Legionella) can oppose absorption of food when devoured by amoebae.[57] The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum.[58] Microorganisms that can overcome the defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts.

Recent evidence indicates that several Amoebozoa lineages undergo meiosis.

Orthologs of genes employed in meiosis of sexual eukaryotes have recently been identified in the Acanthamoeba genome. These genes included Spo11, Mre11, Rad50, Rad51, Rad52, Mnd1, Dmc1, Msh and Mlh.[59] This finding suggests that the ''Acanthamoeba'' are capable of some form of meiosis and may be able to undergo sexual reproduction.

The meiosis-specific recombinase, Dmc1, is required for efficient meiotic homologous recombination, and Dmc1 is expressed in Entamoeba histolytica.[60] The purified Dmc1 from E. histolytica forms presynaptic filaments and catalyses ATP-dependent homologous DNA pairing and DNA strand exchange over at least several thousand base pairs.[60] The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1.[60] These processes are central to meiotic recombination, suggesting that E. histolytica undergoes meiosis.[60]

Studies of Entamoeba invadens found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst, homologous recombination is enhanced.[61] Expression of genes with functions related to the major steps of meiotic recombination also increase during encystations.[61] These findings in E. invadens, combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba.

Dictyostelium discoideum in the supergroup Amoebozoa can undergo mating and sexual reproduction including meiosis when food is scarce.[62][63]

Since the Amoebozoa diverged early from the eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Furthermore, these findings are consistent with the proposal of Lahr et al.[64] that the majority of amoeboid lineages are anciently sexual.

1. ^ "Amoeba" Archived 22 November 2015 at the Wayback Machine at Oxforddictionaries.com

2. David J. Patterson. "Amoebae: Protists Which Move and Feed Using Pseudopodia". Tree of Life web project. Archived from the original on 15 June 2010.

3. ^ "The Amoebae". The University of Edinburgh. Archived from the original on 10 June 2009.

4. ^ Wim van Egmond. "Sun animalcules and amoebas". Microscopy-UK. Archived from the original on 4 November 2005.

5. ^ Flor-Parra, Ignacio; Bernal, Manuel; Zhurinsky, Jacob; Daga, Rafael R. (17 December 2013). "Cell migration and division in amoeboid-like fission yeast". Biology Open. 3 (1): 108-115. doi:10.1242/bio.20136783. ISSN 2046-6390. PMC 3892166. PMID 24357230.

6. ^ Friedl, P.; Borgmann, S.; Bröcker, E. B. (1 October 2001). "Amoeboid leukocyte crawling through extracellular matrix: lessons from the Dictyostelium paradigm of cell movement". Journal of Leukocyte Biology. 70 (4): 491-509. doi:10.1189/jlb.70.4.491. ISSN 0741-5400. PMID 11590185. S2CID 28731650.

7. Marée, Athanasius FM; Hogeweg, Paulien (2001). "How amoeboids self-organize into a fruiting body: multicellular coordination in Dictyostelium discoideum". Proceedings of the National Academy of Sciences. 98 (7): 3879-3883. doi:10.1073/pnas.061535198. PMC 31146. PMID 11274408.

8. ^ Mackerras, M. J.; Ercole, Q. N. (1947). "Observations on the action of paludrine on malarial parasites". Transactions of the Royal Society of Tropical Medicine and Hygiene. 41 (3): 365-376. doi:10.1016/s0035-9203(47)90133-8. PMID 18898714.

9. ^ Jan Pawlowski: The twilight of Sarcodina: a molecular perspective on the polyphyletic origin of amoeboid protists. Protistology, Band 5, 2008, S. 281-302. (pdf, 570 kB) Archived 14 June 2013 at the Wayback Machine

10. ^ Tan; et al. (2005). "A simple mass culture of the amoeba Chaos carolinense: revisit" (PDF). Protistology. 4: 185-90. Archived (PDF) from the original on 29 September 2017.

11. ^ Alberts Eds.; et al. (2007). Molecular Biology of the Cell 5th Edition. New York: Garland Science. p. 1037. ISBN 9780815341055.

12. ^ Margulis, Lynn (2009). Kingdoms and Domains. Academic Press. pp. 206-7. ISBN 978-0-12-373621-5.

13. ^ Ogden, C. G. (1980). An Atlas of Freshwater Testate Amoeba. Oxford, London, and Glasgow: Oxford University Press, for British Museum (Natural History). pp. 1-5. ISBN 978-0198585022.

14. ^ Alberts Eds.; et al. (2007). Molecular Biology of the Cell 5th Edition. New York: Garland Science. p. 663. ISBN 9780815341055.

15. Thorp, James H. (2001). Ecology and Classification of North American Freshwater Invertebrates. San Diego: Academic. p. 71. ^ ISBN 0-12-690647-5.

16. Gooday, A. J.; Aranda da Silva, A.; Pawlowski, J. (1 December 2011). "Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)". Deep-Sea Research Part II: Topical Studies in Oceanography. The Geology, Geochemistry, and Biology of Submarine Canyons West of Portugal. 58 (23-24): 2401-2419. Bibcode:2011DSRII..58.2401G. doi:10.1016/j.dsr2.2011.04.005.

17. ^ "Brain-Eating Amoeba (Naegleria Fowleri): Causes and Symptoms". Archived from the original on 21 August 2016.

18. ^

19. ^

20. ^ Corliss, J. O. (1987). "Protistan phylogeny and eukaryogenesis". International Review of Cytology. 100: 319-370. doi:10.1016/S0074-7696(08)61703-9. ISBN 9780080586373. PMID 3549607.

21. ^ McGrath, Kimberley; Blachford, Stacey, eds. (2001). Gale Encyclopedia of Science Vol. 1: Aardvark-Catalyst (2nd ed.). Gale Group. ISBN 978-0-7876-4370-6. OCLC 46337140.

22. ^ Bütschli, Otto (1882). Klassen und Ordnungen des Thier-Reichs I. Abteilung: Sarkodina und Sporozoa. Paleontologische Entwicklung der Rhisopoda von C. Scwager. p. 1.

23. Park, J. S.; Simpson, A. G. B.; Brown, S.; Cho, B. C. (2009). "Ultrastructure and Molecular Phylogeny of two Heterolobosean Amoebae, Euplaesiobystra hypersalinica gen. Et sp. Nov. And Tulamoeba peronaphora gen. Et sp. Nov., Isolated from an Extremely Hypersaline Habitat". Protist. 160 (2): 265-283. doi:10.1016/j.protis.2008.10.002. PMID 19121603.

24. ^ Greub, G; Raoult, D (2004). "Microorganisms resistant to free-living amoebae". Clinical Microbiology Reviews. 17 (2): 413-433. doi:10.1128/CMR.17.2.413-433.2004. PMC 387402. PMID 15084508.

25. ^ "Are amoebae safe harbors for plague? New research shows that plague bacteria not only survive, but thrive and replicate once ingested by an amoeba".

26. ^ Vidyasagar, Aparna (April 2016). "What Is an Amoeba?". livescience.com.

27. ^ Thewes, Sascha; Soldati, Thierry; Eichinger, Ludwig (2019). "Editorial: Amoebae as Host Models to Study the Interaction with Pathogens". Frontiers in Cellular and Infection Microbiology. 9: 47. doi:10.3389/fcimb.2019.00047. PMC 6433779. PMID 30941316.

28. ^ Kelso AA, Say AF, Sharma D, Ledford LL, Turchick A, Saski CA, King AV, Attaway CC, Temesvari LA, Sehorn MG (2015). "Entamoeba histolytica Dmc1 Catalyzes Homologous DNA Pairing and Strand Exchange That Is Stimulated by Calcium and Hop2-Mnd1". PLOS ONE. 10 (9): e0139399. Bibcode:2015PLoSO..1039399K. doi:10.1371/journal.pone.0139399. PMC 4589404. PMID 26422142.

29. Singh N, Bhattacharya A, Bhattacharya S (2013). "Homologous recombination occurs in Entamoeba and is enhanced during growth stress and stage conversion". PLOS ONE. 8 (9): e74465. Bibcode:2013PLoSO...874465S. doi:10.1371/journal.pone.0074465. PMC 3787063. PMID 24098652.

30. ^

# data[].attributes.attachment_link.description
Toggle the table of contents From Wikipedia, the free encyclopedia An amoeba (; less commonly spelled ameba or amœba; PL : am(o)ebas or am(o)ebae ),[1] often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods.[2]

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What is Amoeba?

Amoeba is a unicellular organism that has the ability to change its shape. They are usually found in water bodies such as ponds, lakes and slow-moving rivers. Sometimes, these unicellular organisms can also make their way inside the human body and cause various illnesses.

One of the first reports referencing amoebas dates can be traced back to 18th century. A German naturalist named August Johann Rösel von Rosenhof who discovered a specimen and made detailed illustrations of the same in 1755.

Structure of Amoeba

Typically, most amoebas are characterized by the following features:

1. Movement occurs through the use of pseudopodia, where the cytoplasm pushes the plasma membrane outward or inward, creating blunt, finger-like projections.

2. There can be multiple pseudopodia at one particular instance, hence, its shape rapidly changes.

3. Structure of amoeba primarily encompasses 3 parts - the cytoplasm, plasma membrane and the nucleus.

4. The cytoplasm can be differentiated into 2 layers - the outer ectoplasm and the inner endoplasm

5. The plasma membrane is a very thin, double-layered membrane composed of protein and lipid molecules.

6. Amoeba also contains other cellular organelles such as a contractile vacuole, mitochondria, Golgi apparatus and fat globules.

7. Amoeba consumes food either through the process of phagocytosis or pinocytosis.

8. The process of reproduction is through asexual means, such as binary fission.

9. The lifespan of a typical amoeba is 2 days, but because it undergoes binary fission, the resultant daughter cells are the same as its parent cell, so technically, amoebas can be termed as immortal.

10. When living conditions are not ideal, an amoeba can essentially transform itself into a protective ball, called a microbial cyst. When living conditions become better, it can revert back to its trophozoite stage, where it can start feeding again.

Amoeba Classification

Traditionally, amoebas are grouped under the Kingdom Protista as they are neither classified as a plant, animal nor fungus. However, amoebas fall under eukaryotes as they possess a true nucleus.

Though technically not a true amoeba, the Naegleria fowleri, or more commonly called the brain-eating amoeba is an amoeboid organism than can make its way into the human body through the nose. It primarily feeds on neurons, thereby destroying the brain tissue. Unsurprisingly, the fatality rate of this infection is high - 97%.

Learn more in detail about Amoeba, its structure, classification and other related topics at BYJU'S Biology.

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Amoeba - Structure and Classification of Amoeba

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Amoeba is a unicellular organism that has the ability to change its shape. They are usually found in water bodies such as ponds, lakes and slow-moving rivers. Sometimes, these unicellular organisms can also make their way inside the human body and cause various illnesses.

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(Image credit: Getty Images )

"Amoeba" is a term that describes a simple eukaryotic organism that moves in a characteristic crawling fashion. However, a comparison of the content of the various amoebas shows that these organisms are not necessarily closely related to each other.

What does an amoeba look like?

All living organisms can be broadly divided into two groups - prokaryotes and eukaryotes - which are distinguished by the relative complexity of their cells. Eukaryotes are highly organized unicellular or multicellular organisms, such as animals and plants. Prokaryotes, on the other hand, are basic single-celled organisms, such as and archaea.
Related: ​​Strange single-celled life-form has a truly bizarre genome
Amoebas are eukaryotes. Their single cells, like those of other eukaryotes, possess certain characteristic features: Their cellular contents are enclosed within a cell membrane, and their is packaged into a central cellular compartment called the nucleus, according to a 2014 report published in the journal BMC Biology (opens in new tab). In addition, they contain specialized structures called organelles, which perform a range of cellular functions including energy production and transport.

Most of these organelles are common to all eukaryotic cells, but there are a few exceptions. For example, the parasitic amoebas Entamoeba histolytica, which cause amoebic dysentery in humans, do not have the golgi apparatus, the responsible for modifying and transporting proteins, according to a 2005 study published in The Journal of Biological Chemistry (opens in new tab). Researchers found that E. histolytica instead contain golgi-like compartments or vesicles - small fluid-filled pouches - that execute similar functions.

There are also amoebas that don't have mitochondria, the organelle responsible for generating cellular energy, because they live in environments lacking in , or "anoxic conditions," Sutherland Maciver, a reader in the department of biomedical sciences at the University of Edinburgh, told Live Science.

According to a 2014 review published in the journal (opens in new tab), these organisms without mitochondria can contain organelles called hydrogenosomes or mitosomes, which are related to mitochondria but are thought to be highly altered versions of the organelle. This is the case for E. histolytica and the free-living amoeba Mastigamoeba balamuthi, which doesn't depend on other organisms for survival.

How does an amoeba move?

Structurally, amoebas closely resemble the cells of higher organisms. "They are like our cells, and in fact, when they are moving they look very much like our white blood cells," Maciver said. (White blood cells are cells that help defend the body against disease.)

Like our white blood cells, amoebas move using pseudopodia, which translates to "false feet" in Latin. These short-lived, outward projections of the cytoplasm - the semifluid material inside the cell membrane - help amoebas to grip a surface and propel themselves forward. As the pseudopodium moves out along a surface in one direction, the back end of the amoeba contracts, Maciver said.
Related: Robert Hooke: English scientist who discovered the cell
"As it contracts, it does two things," he said. "The contraction pushes the cytoplasm forward to fill the expanding pseudopod, but the contraction also pulls up adhesions at the back end of the cell." Maciver describes these adhesions between an amoeba and the surface on which it moves as physical molecular adhesions, which are constantly formed at the front end and broken at the back. This movement, using pseudopodia, is a characteristic that unites various amoebas and distinguishes them from other - simple eukaryotic organisms like amoebas that are not plants, animals or fungi.

Amoebas can also use their pseudopodia to feed. A 1995 report, published in the journal Applied and Environmental Microbiology (opens in new tab), gives the example of the soil-dwelling amoeba Acanthamoeba castellanii, which ingests both solids and liquids using its pseudopodia. The process of ingesting solid material is called phagocytosis, and the process of engulfing drops of liquid is known as pinocytosis, also known as cell drinking, according to Dosage Form Design Considerations (opens in new tab) (Academic Press/Elsevier, 2018).

(Image credit: CDC/ Dr. Mae Melvin)

"Most of the known amoebae eat bacteria," Maciver told Live Science. He explained that amoebas have receptors on their cell surface that bind to bacteria, which are then taken into amoebas by phagocytosis, usually at the rear of the cell.

In the case of giant amoebas, such as Amoeba proteus, the process of phagocytosis is slightly different, according to Maciver. Giant amoebae engulf their prey "by the willful gathering of pseudopods around the bacteria." In both cases, as the bacteria is drawn in, the cell membrane that surrounds it pinches off to form an intra-cellular compartment called the vacuole.

How are amoebas classified?

For centuries, the various systems of classifying organisms, including amoebas, were based on similarities in observable characteristics and morphology. "There isn't actually a coherent group of organisms called the amoebae," Maciver said. "Rather, amoebae are any protozoan cells that move by crawling." (The term "protozoa" refers to a subset of protists, which again are simple eukaryotic organisms that are not plants, animals or fungi, Live Science previously reported.)

Early analyses compared the DNA sequences that encode part of the ribosome, the site of protein synthesis in a cell; specifically, scientists looked at the genes for the so-called 18S subunit of ribosomes, or "SSU rDNA." Based on the analyses of SSU rDNA and other DNA sequences, eukaryotic organisms are now organized in a manner that better represents their evolutionary relationships - the phylogenetic tree, according to the 2008 Protistology article.

Burki listed five supergroups for eukaryotic organisms: Ophiskontha, Amoebozoa, Excavata, Archaeplastida and SAR, which includes three subgroups named Stramenopiles, Alveolata and Rhizaria. Animals and fungi are in the group Ophiskontha. Amoeboid protists and some parasitic lineages that lack mitochondria are part of Amoebozoa. Together, Ophiskontha and Amoebozoa form a larger supergroup called Amorphea, according to the review in the journal Trends in Ecology & Evolution.

(Image credit: Getty Images)

"If you look at the great diversity of the protists, you can see that there are amoebae in virtually all the groups," Maciver said. "There's even an amoeboid organism within the brown algae [Labyrinthula]." Most amoebas are present within the Amoebozoa group, though, Maciver said. In addition, he noted that amoebas are also present within Rhizaria and Excavata. Nucleariids, a group of amoebae with filopodia, belong to the Opisthokonta supergroup, for example, and Labyrinthulids fit within the Stramenopiles.

Why are amoebas important?

Amoebas are known to cause a range of human diseases. Amebiasis, or amoebic dysentery, is an infection caused by E. histolytica, a human intestinal parasite, according to the Centers for Disease Control and Prevention (opens in new tab) (CDC). According to the medical database StatPearls (opens in new tab), E. histolytica can invade the colon wall and cause colitis, where the inner lining of the colon becomes inflamed, and the parasite can cause severe and dysentery.

Though E. histolytica infections can occur anywhere in the world, it is most common in tropical regions that have substandard sanitation systems and crowded conditions.

While the initial symptoms include redness, itchiness and blurred vision, if left untreated the infection can cause severe pain and lead to vision loss, according to the CDC.

Amoebas also cause different infections of the brain. , which has been dubbed "the brain-eating amoeba," causes primary amoebic meningoencephalitis (PAM). Though the disease is rare, it is almost always fatal, according to the (opens in new tab). Early symptoms include fever and vomiting, and the disease ultimately progresses to more severe symptoms such as hallucinations and coma. N. fowleri is present in warm freshwater bodies such as hot springs, lakes and rivers, or in poorly chlorinated swimming pools or contaminated, hot tap water. These amoebas enter from the nose and travel to the brain. However, the infection can't be contracted by swallowing water, according to the CDC.

Early symptoms include headaches, nausea and low-grade fever, partial paralysis, seizures and speech difficulties. B. mandrillaris is found in the soil and can enter the body through open wounds or when people breathe in contaminated dust, according to the CDC. Since the amoeba was discovered in the 1980s, about 200 cases of the infection have been reported worldwide; this includes more than 100 confirmed cases in the U.S.

Maciver cites the example of cooling towers as a place where both amoebas and these bacteria can grow. Cooling towers tend to expel water droplets, which passersby can breathe in. "What's known to happen on many occasions, is that we breathe in a droplet of water containing an amoeba that is full of these pathogens [Legionella]," he said. If bacteria enter the body of an immunocompromised individual in such a manner, they can ultimately infect macrophages, one of the immune system's many defensive cells.

"A macrophage not only looks like an amoeba, its biochemical pathways and cell biology are quite similar," Maciver said. "So the same programmed events that allow the bacteria to escape the amoeba now operate to allow Legionella to escape the macrophage."

Amoebas are also important for recycling nutrients in the soil. According to Maciver, when nutrients become available they are taken up by bacteria, which "effectively lock up all the nutrients in bacterial mass." When bacteria are consumed, nutrients are released back into the soil. "If you have a cycle whereby amoeba eat bacteria, the overall effect is to increase nutrient availability for plants," Maciver said.

Additional resources and readings

Bibliography

Acharya, P. C., Fernandes, C., Mallik, S., Mishra, B., & Tekade, R. K. (2018). Physiologic Factors Related to Drug Absorption. In Dosage form design considerations (Vol. i, pp. 117-147). chapter, Academic Press/Elsevier.
Originally published on Live Science.
Bogitsh, B. J., Carter, C. E., & Oeltmann, T. N. (2019). General Characteristics of the Euprotista (Protozoa). In Human parasitology (fifth edition) (5th ed.). chapter, Academic Press.

Editor's note: This article was last updated on Jan. 28, 2022 by Live Science staff writer Nicoletta Lanese.

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(Image credit: Getty Images ) "Amoeba" is a term that describes a simple eukaryotic organism that moves in a characteristic crawling fashion. However, a comparison of the content of the various amoebas shows that these organisms are not necessarily closely related to each other.

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Chilomonas is a genus of cryptophytes, including the species Chilomonas paramecium . Chilomonas is a protozoa ( heterotroph). Chilomonas is golden brown and has two flagella.

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Other articles where Chilomonas is discussed: algae: Annotated classification: ...approximately 200 described species; includes Chilomonas, Cryptomonas, Falcomonas, Plagioselmis, Rhinomonas, and Teleaulax. Division Rhodophyta (red algae) Predominantly filamentous; mostly photosynthetic, a few

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Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox diverged from unicellular ancestors approximately 200 million years ago.

Volvox is a polyphyletic genus in the volvocine green algae clade. Each mature Volvox colony is composed of up to thousands of cells from two differentiated cell types: numerous flagellate somatic cells and a smaller number of germ cells lacking in soma that are embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of glycoproteins.

Adult somatic cells comprise a single layer with the flagella facing outward. The cells swim in a coordinated fashion, with distinct anterior and posterior poles. The cells have anterior eyespots that enable the colony to swim towards light. The cells of colonies in the more basal Euvolvox clade are interconnected by thin strands of cytoplasm, called protoplasmates. Cell number is specified during development and is dependent on the number of rounds of division.

Reproduction

Volvox is facultatively sexual and can reproduce both sexually and asexually. In the lab, asexual reproduction is most commonly observed; the relative frequencies of sexual and asexual reproduction in the wild is unknown. The switch from asexual to sexual reproduction can be triggered by environmental conditions and by the production of a sex-inducing pheromone. Desiccation-resistant diploid zygotes are produced following successful fertilization.

An asexual colony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motile gonidia in the interior, which produce new colonies through repeated division. In sexual reproduction two types of gametes are produced. Volvox species can be monoecious or dioecious. Male colonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs.

Kirk and Kirk showed that sex-inducing pheromone production can be triggered in somatic cells by a short heat shock given to asexually growing organisms. The induction of sex by heat shock is mediated by oxidative stress that likely also causes oxidative DNA damage. It has been suggested that switching to the sexual pathway is the key to surviving environmental stresses that include heat and drought. Consistent with this idea, the induction of sex involves a signal transduction pathway that is also induced in Volvox by wounding.

Colony inversion

Colony inversion is a special characteristic during development in the order Volvocaceae that results in new colonies having their flagella facing outwards. During this process the asexual reproductive cells (gonidia) first undergo successive cell divisions to form a concave-to-cup-shaped embryo or plakea composed of a single cell layer. Immediately after, the cell layer is inside out compared with the adult configuration-the apical ends of the embryo protoplasts from which flagella are formed, are oriented toward the interior of the plakea. Then the embryo undergoes inversion, during which the cell layer inverts to form a spheroidal daughter colony with the apical ends and flagella of daughter protoplasts positioned outside. This process enables appropriate locomotion of spheroidal colonies of the Volvocaceae. The mechanism of inversion has been investigated extensively at the cellular and molecular levels using the model species, Volvox carteri.

Volvox is a genus of freshwater algae found in ponds and ditches, even in shallow puddles. According to Charles Joseph Chamberlain,

"The most favorable place to look for it is in the deeper ponds, lagoons, and ditches which receive an abundance of rain water. It has been said that where you find , you are likely to find Volvox; and it is true that such water is favorable, but the shading is unfavorable. Look where you find , , , Equisetum fluviatile, Utricularia, , and . Dr. Nieuwland reports that , and are commonly found as constituents of the green scum on wallows in fields where pigs are kept. The flagellate, , is often associated with these forms."

Antonie van Leeuwenhoek first reported observations of Volvox in 1700.

Ancestors of Volvox transitioned from single cells to form multicellular colonies at least 200 million years ago, during the Triassic period. An estimate using DNA sequences from about 45 different species of volvocine green algae, including Volvox, suggests that the transition from single cells to undifferentiated multicellular colonies took about 35 million years.

1. ^ University of Arizona (February 22, 2009). "Single-celled algae took the leap to multicellularity 200 million years ago". Science Daily.

2. ^ Kirk, David L. (1998). Volvox: A Search for the Molecular and Genetic Origins of Multicellularity and Cellular Differentiation. Cambridge University Press. ISBN 978-0-521-45207-6.

3. ^ Hallmann, A. (2003). "Extracellular Matrix and Sex-Inducing Pheromone in Volvox". Extracellular matrix and sex-inducing pheromone in Volvox. International Review of Cytology. 227. pp. 131-182. doi:10.1016/S0074-7696(03)01009-X. ISBN 978-0-12-364631-6. PMID 14518551.

4. ^ Ikushima, N.; Maruyama, S. (1968). "The protoplasmic connection in Volvox". Journal of Eukaryotic Microbiology. 15 (1): 136-140. doi:10.1111/j.1550-7408.1968.tb02098.x.

5. Nedelcu, AM; Michod, RE (2003). "Sex as a response to oxidative stress: the effect of antioxidants on sexual induction in a facultatively sexual lineage". Proc. Biol. Sci. 270 Suppl 2: S136-9. doi:10.1098/rsbl.2003.0062. PMC 1809951. PMID 14667362.

6. ^ Hallmann, Armin (2003). "Extracellular Matrix and Sex-Inducing Pheromone in Volvox". International Review of Cytology. 227: 131-182. doi:10.1016/S0074-7696(03)01009-X. ISBN 9780123646316. PMID 14518551.

7. Powers, J. H. (1908). "Further studies in Volvox, with descriptions of three new species". Transactions of the American Microscopical Society. 28: 141-175. doi:10.2307/3220908. JSTOR 3220908.

8. ^ DL, Kirk; Kirk, MM (1986). "Heat shock elicits production of sexual inducer in Volvox". Science. 231 (4733): 51-4. Bibcode:1986Sci...231...51K. doi:10.1126/science.3941891. PMID 3941891.

9. ^ Nedelcu, AM; Marcu, O; Michod, RE (2004). "Sex as a response to oxidative stress: a twofold increase in cellular reactive oxygen species activates sex genes". Proc. Biol. Sci. 271 (1548): 1591-6. doi:10.1098/rspb.2004.2747. PMC 1691771. PMID 15306305.

10. Amon, P; Haas, E; Sumper, M (1998). "The sex-inducing pheromone and wounding trigger the same set of genes in the multicellular green alga Volvox". Plant Cell. 10 (5): 781-9. doi:10.2307/3870664. JSTOR 3870664. PMC 144025. PMID 9596636.

11. ^ Yamashita, S; Arakaki, Y; Kawai-Toyooka, H; Noga, A; Hirono, M; Nozaki, H (Nov 2016). "Alternative evolution of a spheroidal colony in volvocine algae: developmentalanalysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta)". BMC Evol. Biol. 16 (1): 243. doi:10.1186/s12862-016-0794-x. PMC 5103382. PMID 27829356. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.

12. Stephanie Höhn, Aurelia R. Honerkamp-Smith, Pierre A. Haas, Philipp Khuc Trong, and Raymond E. Goldstein Phys. Rev. Lett. 114, 178101 - Published 27 April 2015. ^ This article contains quotations from this source, which is available under the Creative Commons Attribution 3.0 (CC BY 3.0) license.

13. ^ Chamberlain, Charles Joseph (2007) [1932]. "Chlorophyceae". Methods in Plant Histology. Read Books. pp. 162-180. ISBN 978-1-4086-2795-2.

14. ^ van Leeuwenhoek, Antonie (1700). "Part of a Letter from Mr Antony van Leeuwenhoek, concerning the Worms in Sheeps Livers, Gnats, and Animalcula in the Excrements of Frogs". Philosophical Transactions of the Royal Society. 22 (260-276): 509-518. Bibcode:1700RSPT...22..509V. doi:10.1098/rstl.1700.0013.[permanent dead link ]

15. Herron, M. (2015). "...of the bignefs of a great corn of fand...". ^ Fierce Roller Blog, [1] Archived 2016-06-03 at the Wayback Machine.

16. Baker, H. (1753). ^ Employment for the microscope. R. Dodsley: London, pl. XII, f. 27,[2].

17. Linnaeus, C. (1758). ^ Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Editio decima revisa. Vol. 1 pp. [i-iv], [1]-823. Holmiae [Stockholm]: impensis direct. Laurentii Salvii.

18. Herron, M. (2016). Moving without limbs! Linnaeus on Volvox. ^ Fierce Roller Blog, [3] Archived 2016-06-03 at the Wayback Machine.

19. Spencer, M.A., Irvine, L.M. & Jarvis, C.E. (2009). Typification of Linnaean names relevant to algal nomenclature. ^ Taxon 58: 237-260, [4] Archived 2016-05-08 at the Wayback Machine.

20. Herron, MD; Hackett, JD; Aylward, FO; Michod, RE (2009). "Triassic origin and early radiation of multicellular volvocine algae". Proceedings of the National Academy of Sciences, USA. 106 (9): 3254-3258. Bibcode:2009PNAS..106.3254H. doi:10.1073/pnas.0811205106. PMC 2651347. PMID 19223580.

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Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox diverged from unicellular ancestors approximately 200 million years ago.

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Volvox is a genus of green algae containing around 20 species of freshwater algae. Thousands of cells together form colonies. There are around 500 to 60,000 cells in each colony of volvox. Leeuwenhoek was the first scientist to observe them in 1700. Volvox is widely studied to understand the process of morphogenesis. They live in freshwater habitats such as ponds, ditches, etc. The colour of the pond looks greenish due to the rapid growth of volvox.

Table of Contents:

Volvox Classification

Volvox is classified in the class Chlorophyceae due to the presence of chlorophyll.

Common species are Volvox aureus, Volvox globator, V. carteri, V. barberi, etc.

Volvox Diagram

Also see:
Volvox Characteristics

A single colony of volvox looks like a ball of ~0.5 mm in diameter

The plant body of volvox is a hollow sphere called coenobium, thousands of cells are arranged in the periphery of the sphere

The cells of coenobium are of two types, germ cells and flagellated somatic cells

Extracellular matrix of coenobium is made up of glycoproteins

Individual cells are spherical in shape

They have a cup-shaped chloroplast

Chloroplast contains pyrenoids

The cell has a nucleus, vacuoles and an eyespot

Two equal-sized flagella are present in each cell anteriorly. The coordinated movement of flagella enables the colony to move in the water

Each cell performs all the metabolic functions independently such as respiration, photosynthesis, excretion, etc.

Cytoplasmic strands formed during cell division connects adjacent cells

Polarity exists in the coenobium as cells of the anterior region have bigger eyespots than cells of the posterior region

Eyespot is used for light reception, cells with larger eyespot are grouped together, and they facilitate phototaxis movement

Volvox significantly contribute to the production of oxygen and also many aquatic organisms feed on them

Volvox aureus may multiply rapidly, resulting in the harmful algal bloom (HAB). HAB is more frequent in warm waters having a high nitrogen content

Volvox Life Cycle

The life cycle of Volvox is haplontic, i.e. the dominant stage is free-living haploid (n) gametophyte and the sporophyte is represented only by the diploid zygote (2n)

Volvox show cell differentiation in terms of reproductive and somatic cells

Most of the species reproduce by both mechanism, asexual under the favourable condition and sexual reproduction during the unfavourable condition

In asexual reproduction, reproductive cells known as gonidia produce daughter colonies, which on maturing, are released from the parent

The gonidium undergoes multiple division to form a colony of around 3200 cells

Sexual reproduction is oogamous

Each coenobia may be monoecious or dioecious

Sexual reproduction is by male and female reproductive cells known as spermatozoa and ova respectively

An ovum is produced inside the oogonium. Ova are large and non-motile. They are green in colour due to the presence of chloroplasts. It contains pyrenoids and has food storage

Spermatozoa are produced inside the antheridium in a bunch. Each sperm is spindle-shaped having a pair of apical cilia

Biflagellated antherozoids are released either in a group or individually

Antherozoids get attracted towards oogonium by the chemotactic movement. They break the wall of oogonia by the action of proteolytic enzyme

Out of many sperms that enter, only one antherozoid fertilises the egg

Ova and spermatozoa undergo fertilization to form a diploid zygote

Zygote forms cyst and becomes red due to the accumulation of hematochrome

The zygote detaches from the parent after the disintegration of the parent and remains dormant for a longer duration

The zygote undergoes meiotic cell division to form four haploid cells.

They further undergo multiple mitotic cell division to form a colony and the life cycle continues

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Volvox: Classification, Characteristics with Diagram, Life Cycle and Reproduction

# data[].attributes.attachment_link.description
Volvox is a genus of green algae containing around 20 species of freshwater algae. Thousands of cells together form colonies. There are around 500 to 60,000 cells in each colony of volvox. Leeuwenhoek was the first scientist to observe them in 1700. Volvox is widely studied to understand the process of morphogenesis.

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Volvox: Volvox, genus of some 20 species of freshwater green algae (division Chlorophyta) found worldwide. Volvox form spherical or oval hollow colonies that contain some 500 to 60,000 cells embedded in a gelatinous wall and that are often just visible with the naked eye. Volvox colonies were first