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Most of us are familiar with several of the animals that make up the phylum, or division, Chordata, meaning 'cord,' because it includes humans and many other vertebrates, such as cats and dogs, and they live in marine, freshwater, and land habitats all over the world. Chordates are animals who are vertebrates (having a backbone) or closely related invertebrates (lacking a backbone). Vertebrates and invertebrates, you say? What makes them related? Good question. Let's find out.

Features

If we were to compare a sea squirt and a polar bear, we wouldn't find much in common, would we? The sea squirt is mostly just a mass of transparent jelly with no brain and no sensory organs, and a polar bear has four legs, fur, and excellent senses of smell, eyesight, and hearing. How could they possibly be related?

Well, all chordates have the following features at some point in their lives. Generally, that point is during the embryonic stage (developmental). Many of these features disappear in the adult stage, as in our example of the sea squirt and the polar bear.

Gill slits - these appear in the throat and show the aquatic ancestry of the chordates

Dorsal nerve cord - this cord contains nerve fibers and develops into the spinal cord and brain

Notochord - consisting of cartilage, this is the ancient version of the vertebra or backbone

Post-anal tail

Let's find out what groups make up the Chordata phylum.

Groups

The Chordata share many developmental features, which is how they are grouped. As embryos, they are quite similar, however, these animals are very different from each other as adults. Because of this, the Chordata are divided into three sub-phyla (sub-divisions). These are the Tunicate, the Cephalochordata, and the Craniata.

The Tunicata, meaning 'tunic,' have no brain. The larvae have both a notochord and a nerve cord, which both disappear in the adults. The larvae look similar to tadpoles. As they mature, they lose the ability to swim and anchor themselves to a rock or similar hard surface. The adult looks like a bag enclosed in a slightly harder covering (the tunic) with two siphons for water to enter and exit. As the water circulates through this bag body, food is filtered out, and the water is squirted back into the sea. These are referred to as sea squirts. The free-floating ones are called salps.

The Cephalochordata ( cephalo meaning 'head' and chordata meaning 'cord') also have no brain, although they do have a notochord and a nerve cord and very simple circulatory systems. There are about 25 species of Cephalochordata. They are small and eel-like. They are often called lancelets because of the shape of their bodies. They prefer coastal waters of the tropical and temperate areas of the world. They burrow into the sand in shallow waters where there is a current bringing food they can grab with their tentacles.

The last sub-phyla of the Chordata are the Craniata, meaning 'cranium.' This group is composed of vertebrates and hagfish and is the only group within the Chordata that have skulls. All craniates have a dorsal nerve cord surrounded by either cartilage (notochord) or bony vertebrae (backbone). Hagfish have partial skulls but no vertebrae, so they are not vertebrates. True vertebrates have a brain, a skull, plus a backbone.

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groups & characteristics - video & lesson transcript | study.com

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Chordates: Features, Groups & Characteristics - Video & Lesson Transcript | Study.com

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Most of us are familiar with several of the animals that make up the phylum, or division, Chordata, meaning 'cord,' because it includes humans and many other vertebrates, such as cats and dogs, and they live in marine, freshwater, and land habitats all over the world.

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- Urochordata
- Cephalachordata
- Vertebrata

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- contains 43,700 species
- Endoskeleton is permanent with vertebrata
- The subphylum vertebrata is divided into seven classes: jawless fish, cartilaginous fish, bony fish, amphibians, reptiles, birds, and mammals.

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-  mostly contains backbones
- Notochord
- Pharynx
- dorsal, hallow nervous system
- verebral column

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- Includes humans
- Gill slits - these appear in the throat and show the aquatic ancestry of the chordates
- Dorsal nerve cord - this cord contains nerve fibers and develops into the spinal cord and brain
-  Notochord- cartilage
- Post- anal tail

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Echinoderms (starfish, brittle star, sea urchin, feather star, sea cucumber)

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Echinoderms (starfish, brittle star, sea urchin, feather star, sea cucumber) - marine biology (characteristics, ecology and range, behavior), underwater photography, links, books

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Biology 40s phylum project. Credits to Leilani Kalb for video at the end and google for the awesome pics!!

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- 5-part radial symmetry
- water based vascular system
- They can regenerate body parts asexually
- If split each side could create a new body

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- Starfish
- Sea Urchin
- Sea Cucumber
- Brittle star
- Blastoid

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- The water-vascular system consists of a circular passageway, the ring canal, that surrounds the digestive tract and five radial canals that radiate from the ring canal like spokes of a wheel. Each radial canal underlies an ambulacral area.
- most species reproduce sexually
- Fertilization occurs out of the body

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- Multi-celled
- radial Symmetry
- No heart, brain, eyes
- tentacle like structures called tube feet. These tube feet are hydraulically controlled by a remarkable vascular system. This system supplies water through canals of small muscular tubes to the tube feet
- when water returns to canals suctions is released

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Arthropods are a very diverse group of organisms that includes insects, crabs, lobsters, scorpions and centipedes. Learn about arthropod characteristics, classification, and examples of marine arthropods.

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Stockbyte/Stockbyte/Getty Images

Arthropods, members of the phylum Arthropoda, are a diverse group of animals including insects, crustaceans, spiders, scorpions and centipedes. However, the members of this phylum, despite their incredible diversity and sheer numbers, share a number of important distinguishing characteristics.

Exoskeleton

Arthropods are invertebrates, which means their bodies do not have internal bones for support. To compensate for this, they produce a hard exoskeleton made of chitin, a mixture of lipids, carbohydrates and protein, which covers and protects their bodies like a suit of armor. As arthropods grow, they must shed or molt their exoskeletons. They first produce new, softer exoskeletons underneath the old ones. Once their hardened, old coverings crack and shed, they sport roomier, albeit soft, exoskeletons. Arthropods are incredibly vulnerable during the molting process, and will often hide until their new exoskeletons harden.

Author

Christina Stephens is a writer from Portland, Ore. whose main areas of focus are pets and animals, travel and literature. A veterinary assistant, she taught English in South Korea and holds a BA in English with cum laude honors from Portland State University.

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Arthropods, members of the phylum Arthropoda, are a diverse group of animals including insects, crustaceans, spiders, scorpions and centipedes. However, the members of this phylum, despite their incredible diversity and sheer numbers, share a number of important distinguishing characteristics. Arthropods are invertebrates, which means their bodies do not have internal bones for support.

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Complex Animals: Annelids & Arthropods - CrashCourse Biology #23

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Hank continues our exploration of animal phyla with the more complexly organized annelida and arthropoda, and a biolography on insects. Crash Course Biology is now available on DVD!

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- Lobsters
- Crabs
- Horseshoe crabs
- Sea Spiders
- Barnacles
- Isopods
- Copepod

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- They go through molting
- Bilaterl symmetry
- jointed legs
- Hard shell

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- Jointed appendages that allow for flexibility and movement
- open circulatory system (blood is pumped through open veins)
- Segmented bodies
- They have no bones but instead have a hard shell, as they grow older they must shed this armor and grow a new one (molting)

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- Bilateral symmetry (vertical into two mirror images)
- Spiral and determinate cleavage

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General Characteristics of Phylum Mollusca:

1. Habitat:

They are mostly marine. Many, however, occur in fresh water and some even in damp soil.

2. Body Form:

The body of molluscs is un-segmented with a distinct head, muscular foot and visceral hump. Neopilina is a segmented mollusc.

3. Symmetry:

They usually show bilateral symmetry. In some molluscs like Pila, due to torsion (twisting) during growth, the adults become asymmetrical.

4. Shell:

Shell is secreted by mantle. It is made up of calcium carbonate. Shell may be external (e.g., most of molluscs), internal (e.g., slug, cuttle fish, squid) or absent (e.g., Octopus).

5. Mantle (Pallium):

It is a thin, fleshy fold of dorsal body wall more or less covering the body. It encloses a space, which is called mantle cavity (= pallial cavity).

6. Body wall:

Single layered epidermis is usually ciliated. Muscles are un-striped and occur in bundles.

7. Body cavity:

Coelom is greatly reduced. It is restricted to pericardial cavity (space around the fieart), and to small spaces within kidneys and gonads (testes and ovaries). Spaces amongst the viscera (soft organs) contain blood and form haemocoel.

8. Digestive tract:

It is complete.

9. Blood vascular system:

It is open type. It includes dorsal heart, arteries that open into sinuses; (spaces) and veins. Blood is usually blue due to the presence of a copper- containing blue respiratory pigment called haemocyanin. Among the molluscs, cuttle fish are exceptional in having closed blood vascular system.

10. Respirator, organs:

These are gills (cteoidia). Mantle and pulmonary sae (in semi-terrestrial form).

11. Excretory organs:

Excretory organs are one or two pairs of sac- like kidneys. Gills are also excretory in function. Ammonia is chief excretory matter.

12. Nervous System:

The nervous system comprises paired cerebral, pleural, pedal and visceral ganglia joined by the nerve connectives and conumssures. Connectives connect dissimilar ganglia; however, commissures connect similar ganglia

13. Sense Organs:

In many molluscs, eyes are present over stalks called ommatophores. Statocysts (balancing organs) may be present. Osphradium is present in some molluscs for testing chemical and physical nature of water.

14. Sexes:

The sexes are generally separate but some are hermaphrodite.

15. Development:

They are oviparous. The development is either direct or indirect (metamorphosis). When the development is indirect it includes a characteristic larva, liger, trochophore or glochidium. Asexual reproduction is absent.

Unique Features:

(i) Mantle covers the body,

(ii) Mantle may be surrounded by shell, and

(iii) Nervous system consists of cerebral, visceral, pleural and pedal ganglia.

Advancement over Annelids:

(i) Shell is present in many individuals,

(ii) In some forms, a lungs is present for pulmonary respiration, and

(iii) Better developed sense organs such as eyes, statocysts and osphradia.

Classification of Phylum Mollusca:

Phylum Mollusca are divided into six classes.

Class 1. Monoplacophora (Gk. monas- one, plax- plate, pherein- bearing):

The shell is spoon or cup shaped. They have die characters of both the phylum Annelida and phylum Mollusca.

Example:

Neopilina.

Class 2. Amphineura (Gk. amphi- both + two neuron = nerve):

There is a present non-ganglionated nerve ring around mouth with two pairs of interconnected nerve cord.

Examples:

Chaetopleura (Chiton).

Class 3. Scaphopoda (Gk. scapha- boat, podos-foot):

Shell is tubular and open at both ends.

Example:

Dentalium.

Class 4. Gastropoda (Gk. gaster- belly, podos- foot):

Shell is made up of one piece.

The early embryo is symmetrical but during development the body twists showing torsion so that the body becomes asymmetrical. It includes the largest number of molluscs e.g., Pila, Umax, Cypraea (Cowrie), Helix (garden snail), Aplysia (sea hare), Doris (sea lemon), Limnaea, (pond snail), Planorbis, Patella (true limpet), Turbinella (Shankh), Creseis (Sea butterfly).

Class 5. Pelecypoda or Lamellibranchiate or Bivalvia (Gk. pelekus- hatchet Podos foot):

Shells is made up of two halves.

Examples:

Unio, Mytilus (Sea mussel), Teredo SpwoS EnZ (razor shell or razor clam), Solen (razor fish or razor shell), Ostrea (edible oyster), Pecten (scallop), Pinctada (Pearl oyster).

Class 6. Cephalopoda (Gk. kephale- head, podos- foot):

Head and foot region combined and modified into a structure which has eyes and eight tentacles, hence the name cephalopod or 'head foot'. Cephalopods are regarded at the top of invertebrates evolution in terms of learned behaviour they exihibit. Shell is external (Nautilus), internal (sepia) or absent (octopus).

Examples:

Sepia, Loligo, octopus, nautilus, (pearly nautilus). Some cephalopods are the largest invertebrates.

Evolutionary Precursor of Molluscs:

A "living fossil" named Neopilina discovered in 1952 from the Pacific Ocean, shows metameric segmentation which is not a characteristic of molluscs. Neopilina has 8 pairs of muscles, 5 or 6 pairs of gills, and 5 pairs of nephridia.

Metameric segmentation and presence of the trochophore larva in both annelids and molluscs suggest that molluscs have descended from the annelids. Thus, the annelids are the evolutionary precursor of molluscs. Neopilina is a "connecting link" between Annelida and Mollusca.

Chiton-The coat of mail shell:

Chiton is marine and found attached to rocks by its foot the shell consists of a row of eight plates.

Dentalium- The Elephant's tusk-shell:

It is a marine mollusc. Dentalium is found burrowing in sand. The shell is slightly curved, tubular and opens at both the ends. There are present filamentous tentacles called the captacula, which are useful in feeding.

Unio (Fresh Water Mussel):

It is found in rivers, lakes and ponds. The animal is omnivorous feeding on microscopic organisms. Its larva lives as parasite on fish. Its shell consists of two halves, called the valves. A whitish elevation in each valve is called umbo.

The lines of growth indicate the age of the individual. There are present two siphons posteriorly. It acts as scavenger and keeps water clean. Its shell yields an excellent quantity of lime the shells of the fresh water mussels are used in the manufacture of buttons.

Pila (Apple snail):

It inhabits ponds, paddy fields, sometimes streams and rivers It is chiefly hetmvorous and feeds on aquatic plants like Pistia and Valusnena. It leads an amohibious life respiring by means of gill in water and by a pulmonary sac an and. Thus it is adapted for both aquatic and terrestrial life.

The mouth or aperture of the shell is closed by a flat and oval plate, the operculum. Pila has osphradium which is meant for testing chemical and physical nature of water. The buccal cavity of Pila contains a rasping organ, the radula, with transverse rows of teeth for cutting the grasses.

Limax (Grey Slug):

It is terrestrial and is abundantly found in gardens, cultivated lands and over damp soil. It is nocturnal and herbivorous. Shell is internal. It is a hermaphrodite animal. The slug is a plant pest. It damages seedlings, tender shoots and leaves.

Sepia (Cuttle fish):

It is a marine and a good swimmer. In male the left arm is spoon shaped and is called hectocotylized which is used to transfer sperms into the female. The shell is internal. A pear-shaped ink-sac containing the ink-like fluid is present.

When the animal is attacked ink-like fluid is ejected through the funnel to form a smoke cloud. Sepia is edible. Sepia ink obtained from this animal is used by artists. The shell of sepia is used as a source of calcium for pet birds.

Lolieo (Squid):

Like Sepia, it is also found in the warm seas. It also ejects a dark ink to form a smoke cloud to escape from .the enemy. Its body resembles that of Sepia in form except that it is narrower than that of Sepia. It also has internal shell Largest.living invertebrate is giant squid (Architeuthis) up to 18 meters long. LxAigo is edible. The giant squid has the largest eye in the animal kingdom.

Octovus (Devil fish):

It is also marine. It kills its prey with poisonous saliva. One of the arms of male is spoon shaped and is called hectocotylized which is used to transfer sperms into the female. The shell is absent. Octopus ejects an inky fluid in water and forms a screen for defence from its enemies. Octopus can change its colour.

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Phylum Mollusca: Characters and Classification (With Diagram) | Animals

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ADVERTISEMENTS: In this article we will discuss about the general characters and classification of Phylum Mollusca. General Characteristics of Phylum Mollusca: 1. Habitat: They are mostly marine. Many, however, occur in fresh water and some even in damp soil. ADVERTISEMENTS: 2. Body Form: The body of molluscs is un-segmented with a distinct head, muscular foot ...

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SNAILS AND THEIR RELATIVES

© Jonathan Bird/ORG
For educational use only

There are over 50,000 known species of Mollusks, which makes them second only to the Arthropods in invertebrate phylum size. Among the Mollusks are some of the most well known of invertebrate sea creatures, like snails, clams, mussels, squid, and octopods. Although one might not see an obvious physical relationship between a snail and a squid, they are remarkably similar in construction.

In general, mollusks have 3 body regions: a head, a visceral mass, and a "foot." The head contains the sense organs and "brain," while the visceral mass contains the internal organs. The "foot" is the muscular lower part of the body which is in contact with the substrate. Mollusks usually have a shell (although some do not). Mollusks also have an extension of the body wall called the mantle. This portion of the animal's anatomy is responsible for secreting the shell. The mantle encloses the mantle cavity which contains the Ctenidia (gills), anus and excretory pores.

Many mollusks have a radula, a tongue of sorts, which is rough like sandpaper and is used to rasp away at food. The radula is made of a hard material called chitin, the same material of which Arthropod exoskeletons are made. In addition, some Mollusk radulae are impregnated with magnetite to give them superior wear characteristics.

Mollusks have well developed body organs (nervous system, circulatory system, respiratory system, etc.) but lack body segmentation.

There are seven classes of Mollusks: Monoplacophora, Polyplacophora, Aplacophora, Gastropoda, Scaphapoda, Bivalvia and Cephalopoda. Of these, Monoplacophora, Aplacophora and Scaphapoda are rare and/or extremely deep-water creatures, and will not be discussed.
The Class Gastropoda
The class Gastropoda (meaning "stomach-foot") contains about 70% of the Molluscan species (around 35,000). These are the familiar snails, limpets, nudibranchs and abalones. The snails, limpets and abalones have a shell while the slugs and nudibranchs do not. There are a small number of land Gastropods such as some snails, slugs, etc.
The Class Polyplacophora
Members of the class Polyplacophora (meaning "many-plated") are more commonly called the chitons (pronounced Kie-tuns). These creatures have eight plates and outwardly resemble the "pill-bugs" which are common under logs and rocks in the forest (they are not related, however). Chitons crawl along rocks and forage for food (mostly algae) using their radulae to scrape it off of the substrate. Magnetite is used for hardening the teeth of the radula in chitons, so they can scrape coraline algae off of rocks. These teeth are so hard that they can etch glass!

These creatures are extremely slow moving. In a year, a chiton may not move more than ten feet. They can detect the presence of light with primitive eyes embedded in the shell plates.
The Class Bivalvia
The bivalves (meaning "two-shells") are perhaps the most well known mollusks simply because of their history as a source of food. Clams, mussels, oysters and scallops are all bivalves. There are about 15,000 known species of bivalve, with about 80% of them being marine (the rest are found in fresh water).

The bivalve may either burrow through the bottom, or attach itself to the substrate with glue-like strings called "byssal threads." Some scallops do not attach themselves because they prefer to be able to swim away with a squirt of water forced from the mantle.

Most bivalves feed by filtering organic particles from water, and therefore do not have a radula. The gills are used in feeding by means of a mucous coating which traps food particles as water passes through them. Some of the giant clams found in the Pacific have symbiotic algae in their mantle tissue, and can utilize the light of the sun to make food, although they still filter feed as well.

The shell is generated by the mantle from the inside. Pearls are made by clams, oysters and mussels when a grain of sand or other small irritant becomes painfully stuck in the mantle of the creature. The bivalve coats the irritant with the same material which is secreted to produce the inner lining of the shell. This makes the irritant smooth, and theoretically, less painful to the bivalve. Although many people think of pearls as coming only from oysters, most bivalves can produce pearls, as well as some snails, like the conch.
The Class Cephalopoda
Although we usually think of Mollusks as benthic (bottom dwelling), the cephalopods have taken to a nektonic (swimming), rather than benthic, existence in the ocean.

Squid, octopods, cuttlefish and nautiluses are all members of the class cephalopoda, meaning "head-footed." This term stems from the way a cephalopod's body is constructed. The "feet" (usually called arms or mistakenly called tentacles) are attached to the part of the body containing the eyes (the "head") while the rest of the body is out in front of the head. Thus, the body does not connect directly to the arms.

The cephalopods may not seem very closely related to the other mollusks, but physiologically, they are similar in internal construction. Perhaps the most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. The octopods do not have shells at all, and the squid have a small chitinized internal shell. Nautiluses are the only Cephalopods with an external shell. Nautiluses are found in the South Pacific and Indian oceans.

Cephalopods have the most well developed nervous systems of all mollusks, as well as the most well developed eye. The cephalopod eye is one of the most notable examples of convergent evolution in all of the animal world, because this eye evolved from a completely different direction than the mammalian eye, yet it turned out to function in almost the exact same way. Cephalopods, therefore, have extremely good eyesight.

This eyesight is well suited for finding prey. The cephalopod then grasps the prey firmly with its arms and eats the prey with a mouth located between the arms. Cephalopods also have a beak, very similar to that of a parrot, used to help bite into prey.

The Blue-Ringed octopus of the South Pacific has a salivary gland which secretes a venom to subdue prey. The venom is so powerful that the bite of this octopus is almost always lethal to a human. Fortunately, it takes a lot of provocation to get an octopus--any octopus--to bite a person.

While the octopus has eight sucker-equipped arms, the squid actually has ten. Eight of the squid arms are of the same length, while the other two are extra long, and are used for helping to grab prey. These two additional arms are called the tentacles.

Cephalopods do share many characteristic molluscan traits with the rest of the creatures in the phylum, such as the presence of a mantle and mantle cavity, a radula in the mouth and a U-shaped digestive tract (useful for a creature in a conical shell, but not necessary for a Cephalopod).
Octopuses or Octopi?
Many people get confused about the proper plural for the word octopus. Octopus is frequently given a Latin plural, yet the word derives its second root from Greek, not Latin (the english "foot" root from Latin is "pod" or "ped", while from Greek it is "pus"). What is the proper plural, anyway? Many say "octopi." The singular looks like a Latin masculine singular, ending in "us," but it really isn't, so pluralizing it to "octopi" is not correct. Most people also mispronounce it as well. If it were "octopi," it would be pronounced "octo-pee" not "octo-pie," and that sounds silly! So, the correct plural is "octopuses," believe it or not. I prefer not to use either of them. Every time you say "octopuses" someone will correct you, and you end up in an argument. So I like to use "octopods," which is the proper plural of the taxonomic order Octopoda, containing the eight-armed cephalopods.

Big Gastropod: The conch (pronounced "konk") is a big snail. There are two eyes on stalks peeking out from under the shell. The points on the shell protect it from other animals. This conch weighs more than a pound!

Colorful Gastropod:
This is a nudibranch, basically a snail without a shell. The word "nudibranch" meansnaked gill. The tuft of yellow on the right side is the animal's gill cluster. Nobody is sure why some nudibranchs are so brightly colored. Some beleive that the coloration is aposematic, meaning that it tells other animals "Danger! I don't taste good!"

A chiton is stuck to a rock. It may not look like much, but getting it off the rock is nearly impossibel!

This is the scallop that most people never see. This bivalve has hundreds of tiny eyes to keep a lookout for predators (those are the tiny black dots around the opening). The animal feeds by filtering food from the water.

This is the Caribbean Reef squid, an animal capable of amazing color changes. Using chromatophores in its skin, the squid can go from white to blue to gold in the blink of an eye. It can jet off at high speed by squirting water though its nozzle, or it can hover in one place with its fins.

The Common Caribbean octopus on the prowl at night, looking for food.

Giant Clams live in the tropical Indo-Pacific and reach several hundred pounds in weight. They have symbiotic algae in their mantle tissue that harvests the sun's energy so they need strong sunlight to survive. Watch the Emmy Award-winning educational underwater adventure program:

JONATHAN BIRD'S BLUE WORLD

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SNAILS AND THEIR RELATIVES © Jonathan Bird/ORG For educational use only There are over 50,000 known species of Mollusks, which makes them second only to the Arthropods in invertebrate phylum size. Among the Mollusks are some of the most well known of invertebrate sea creatures, like snails, clams, mussels, squid, and octopods.

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Kingdom Animalia: Phylum Mollusca | iKen | iKen App | iKen Edu

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- snails
- oysters
- slugs
- clams
- scallops
- cuttlefish
- squid
- octopus

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- Mantle covers whole body
- Mantle may be surrounded by shell
- Nervous system consists of cerebral, visceral, pleural

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- mollusks have 3 body regions: a head, a visceral mass, and a foot
- Head has the sense organs and brain, while the visceral mass contains internal organs
-the foot is the muscular lower part of the body which is in contact with the substrate.
- Mollusks typically have a shell and a an extension of the body wall called the mantle
- Mollusks have tongues that are used to grab at food
- They have no body segmentation

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- mostly marine, but some in damp soil and fresh water
- Bilateral symmetry
- shell is made up of calcium carbonate
- The sexes are generally separate but some are hermaphrodite.
- It is open type. It includes dorsal heart, arteries that open into sinuses; (spaces) and veins. Blood is usually blue due to the presence of a copper- containing blue respiratory pigment called haemocyanin.

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1. Symmetry and Size

Annelids are all bilaterally symmetrical animals. They range in size from much less than 1 mm in length to more than 3 m. The smallest annelids described to date would appear to be Neotenotrocha (Dorvilleidae, Eunicida) reaching only a few hundred microns in length (Eibye-Jacobsen and Kristensen, 1994). Also within Eunicida may be found the largest of annelids. A preserved specimen of Eunice (Eunicidae) at the Museum of Natural History in Washington D. C. is close to 3 m in length and around 5 cm in diameter in its preserved and contracted condition. Some earthworms, such as the Giant Gippsland Earthworm ( Megascolides australis), can reach 1 m in length. The largest leech in the world, Haementeria ghilianii, is found in South America and reaches more than 40 cm in length.

2. Coelom

Nearly all annelids have a fluid-filled cavity between the outer body wall and the gut, and this is referred to as a coelom (Figure 1). The coelom is often used as a storage area for gametes and acts as a hydrostatic skeleton for locomotion. The coelom (formed via schizocoely) is generally organized as a series of compartments divided by intersegmental septa. This compartmentalization means that if the worm is damaged the coelomic contents will only be lost from a few segments, and locomotion can be maintained. In other annelids there may only be a few septa dividing the coelom. Under these circumstances much more coelomic fluid is lost with injury, and the worm may be severely affected. A number of groups, particularly leeches and a number of small polychaetes, have little or no coelomic space.

3. Body wall

Annelids have a body covered by an external cuticle that is never shed or molted. Epidermal microvilli secrete a network of fibers that are in part collagenous and also contain scleroprotein. Chaetae are also cuticular structures, but contain large amounts of chitin. Beneath the epidermis and its basal lamina lies a layer of circular muscle. The circular muscle layer forms a nearly continuous sheath around the body, except in polychaetes with well-developed parapodia. Beneath the circular muscle layer lie thick longitudinal muscles. In many annelids the longitudinal muscles are present as four distinct bands (Fig. 2).

4. Parapodia

Parapodia are unjointed segmental extensions of the body wall found in many polychaetes, though many do lack these features. They are also absent in Clitellata and Echiura. Parapodia are equipped with musculature derived mainly from the circular muscle layer and usually carry chaetae. Parapodia vary in structure but basically can be considered to consist of two elements; a dorsal notopodium and a ventral neuropodium (Fig. 3). In addition to bundles of chaetae, noto- and neuropodia can also have a variety of cirri and gills. They are most elaborate in actively crawling or swimming forms where they form large fleshy lobes that act as paddles. Parapodia of burrowing or tubicolous polychaetes can simply be slightly raised ridges carrying hooked chaetae called uncini.

5. Nervous system

Annelids have a brain or cerebral ganglion that originates and usually resides in the head. The brain varies in structure, with mobile active forms having the most complex brains, and sessile or burrowing forms having simple brains with little differentiation. It is connected to the ventral nerve cord by the circumpharyngeal connectives, which run down each side of the pharynx. The ventral nerve cord, is usually made up of a pair of cords that are bound together and runs the length of the body (Fig. 4). It varies in thickness and dilates into a ganglion in each segment, from which pairs of segmental nerves pass out to the body wall, muscles and gut.

6. Sense organs

There are six major kinds of sensory structures found in annelids. These include palps, antennae, eyes, statocysts, nuchal organs and lateral organs (Fig. 5). Palps and antennae are located on the head of many polychaetes. In some groups they are both sensory while in others the palps are used for feeding. Nuchal organs are ciliated, paired, chemosensory structures, innervated from the posterior part of the brain. They are present in nearly all polychaetes, and Rouse and Fauchald (1997) suggested that they may represent an apomorphy for Polychaeta. This has been challenged by other authors who suggest that nuchal organs may be an apomorphy for Annelida as a whole and have been lost in Clitellata/Oligochaeta (Purschke et al., 2000). Annelids also have a variety of epidermal sensory cells that may be responsive to light or touch (such as lateral organs).

7. Circulation and respiratory structures

A closed circulatory system is present in most polychaetes (Fig. 6), Echiura and many clitellates. It is reduced or absent in leeches where it may be replaced by coelomic canals. A limited circulatory system in which some of the major blood vessels are present but the distal capillary vessels are missing is found in a number of polychaete groups. A circulatory system is absent in many small polychaetes.

8. Segmental organs

In most annelids there are usually two fluid systems, the coelom and the circulatory system, and both (if present) are involved in the excretion of waste products. To achieve this excretion there must be ducts to the exterior, and these are generally referred to as nephridia. Ducts, known as gonoducts or coelomoducts, are also required for the transfer of gametes that develop in the coelom to the outside of the body on maturity. The two different kinds of ducts are often simply referred to as segmental organs since determining what kind of duct is present is problematic.

References

Eibye-Jacobsen, D., and R. M. Kristensen. 1994. A new genus and species of Dorvilleidae (Annelida, Polychaeta) from Bermuda, with a phylogenetic analysis of Dorvilleidae, Iphitimidae and Dinophilidae. Zoologica Scripta 23:107-131.

Pleijel, F., and G. W. Rouse. 2000. A new taxon, capricornia (Hesionidae, Polychaeta), illustrating the LITU ('Least-inclusive taxonomic unit') concept. Zoologica Scripta 29:157-168.

Purschke, G., R. Hessling, and W. Westheide. 2000. The phylogenetic position of the Clitellata and the Echiura - on the problematic assessment of absent characters. Journal of Zoological Systematics and Evolutionary Research 38:165-173.

Rouse, G. W., and K. Fauchald. 1997. Cladistics and polychaetes. Zoologica Scripta 26:139-204.

Rouse, G. W., and F. Pleijel. 2001. Polychaetes. Oxford University Press, London.

About This Page

Greg W. Rouse
Scripps Institution of Oceanography

Fredrik Pleijel
Muséum national d'Histoire naturelle Paris, France

Page: Tree of Life Characteristics of Annelida: Plesiomorphies and Other Features Authored by Greg W. Rouse and Fredrik Pleijel. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

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1. Symmetry and Size Annelids are all bilaterally symmetrical animals. They range in size from much less than 1 mm in length to more than 3 m. The smallest annelids described to date would appear to be Neotenotrocha (Dorvilleidae, Eunicida) reaching only a few hundred microns in length (Eibye-Jacobsen and Kristensen, 1994).

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The annelids include earthworms, polychaete worms, and leeches. All members of the group are to some extent segmented, in other words, made up of segments that are formed by subdivisions that partially transect the body cavity. Segmentation is also called metamerism. Segments each contain elements of such body systems as circulatory, nervous, and excretory tracts.

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- it contains coelom between the outer body wall and the gut
- Annelids are bilaterally smmetrical
- Their is never shed or molted
- They're body is made up of segments
- They have a brain
- their sense organs
- a closed circulatory system

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-  marine, freshwater, and terrestrial earth worms
- marine, fresh water leeches

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- Contains a mouth and an anus
- gases are exchanged through skin or through gills
- They're bodies are segmented
- The body wall is characterized by being made up of both circular and longitudinal muscle fibers surrounded by a moist, acellular cuticle that is secreted by an epidermal epithelium

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- Triploblastic
- Protostome
- All members are to some extent segmented formed by subdivisions
- Segments each contain elements such as body systems as circulatory, nervous and excretory tracts.
- Segmentation allows muscle contraction makes it localalized
- they have 6 sensory structures palps, antennae, eyes, statocysts, nuchal organs and lateral organs

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Jupiterimages/Photos.com/Getty Images

Flatworms belong to the phylum Platyhelminthes, literally meaning "flatworms" in Latin. Flatworm species are divided into three classes: Turbellaria, Trematoda and Cestoda. All flatworms, according to Cool Galapagos, are hermaphroditic, soft-bodied worms with rudimentary nervous systems, no respiratory or circulatory systems and simple digestive tracts with single openings.

Turbellaria

The class Turbellaria is composed of approximately 3,000 species of planaria. Planaria flatworms are typically nonparasitic, and can be found in fresh water, saltwater, and, less often, moist soil. According to Animal Planet, planarians use their cilia to glide through their environment. They can also move short distances using a brisk crawling motion. They feed on protozoa, bacteria, crustaceans, smaller worms, and animal and plant matter.

The Food Chain

Flatworms, according to Cool Galapagos, occupy varying links in food chains. As parasites, Cestodes and Trematodes are at the top of their respective food chains. They are eaten but not digested, or not consumed at all. On the other hand, Turbellarians are a regular food source for fish, amphibians, crustaceans and beetles. They also benefit the environment by consuming and regulating populations of protozoa, algae and rotifers.

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Flatworms belong to the phylum Platyhelminthes, literally meaning "flatworms" in Latin. Flatworm species are divided into three classes: Turbellaria, Trematoda and Cestoda. All flatworms, according to Cool Galapagos, are hermaphroditic, soft-bodied worms with rudimentary nervous systems, no respiratory or circulatory systems and simple digestive tracts with single openings.

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Platyhelminthes: A Big Word for Flatworms

Let's say you're on a trip at the nature center. As you and your friends explore, you come across a big tank with many ocean organisms inside. You see what looks like a colorful piece of paper moving along slowly at the bottom of the tank. 'What is that?' You ask your guide Marlon.

Marlon tells you that the creature is a flatworm, a member of the phylum Platyhelminthes. 'Wow,' You say. 'What a weird looking animal!' Marlon goes on to explain that this little guy and his relatives are the stars of a new exhibit dedicated to the phylum as he leads you through your exploration of the Platyhelminthes exhibit.

General Characteristics of Platyhelminthes

Platyhelminthes is a very interesting phylum that contains nearly 20,000 species. These organisms are generally hermaphrodites, meaning they can have both male and female sexual organs and can produce offspring on their own. They're also soft-bodied invertebrates (they have no spine), and much like humans, flatworms have bilateral symmetry, which means that if you drew a vertical line down the middle of the animal, the left side of the organism would mirror the right side.

Most flatworms also do not have a body cavity! This means most flatworms really don't have anything inside but a small gut, and some don't even have that. They have a small opening through which they take in food and use the same opening to expel waste. Lastly, Platyhelminthes species range in size from microscopic to a few feet long, and they breathe across the whole body!

Examples of Platyhelminthes

As you go deeper into the nature center's Platyhelminthes exhibit, you see four different areas, each dedicated to the four classes of flatworms:

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characteristics & examples - video & lesson transcript | study.com

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Platyhelminthes: Definition, Characteristics & Examples - Video & Lesson Transcript | Study.com

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Let's say you're on a trip at the nature center. As you and your friends explore, you come across a big tank with many ocean organisms inside. You see what looks like a colorful piece of paper moving along slowly at the bottom of the tank. 'What is that?'

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Kingdom Animalia: Phylum Platyhelminthes | Biology | iKen | iKenEdu | iKenApp

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- Bilaterally symmetrical
- no internal cavity
- has mouth but no anus
- dorsoventrally flattened
- contains 3 tissues and has 3 organs and organelles

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- Trematoda
- Cestoda
- Turbellaria
- Flatworms
- Tapeworms

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- Flatworms are dorso-ventrally flattened
- The epidermis is ciliated in the turbellarians, while trematodes and cestodes are capsuled by a cuticle
- It has a saclike digestive cavity, with a single opening that is used as the mouth and anus

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- They have a flattened shape, therefore oxygen and nutrients can pass through their bodies by diffusion
- Bilaterally symmetrical
- Body having 3 layers of tissues with organs and organelles
- no internal cavity
- possesses a blind gut (opened only at one end)
- has a nervous system with longitudinal fibres
- feeds on smaller life forms

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Rotifers are microscopic aquatic animals of the phylum Rotifera. Rotifers can be found in many freshwater environments and in moist soil, where they inhabit the thin films of water that are formed around soil particles.

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Rotifera: A visual celebration of the smallest animals

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- They're microscopic aquatic animals
- They live in still water environments like the bottom of lakes
- Their size makes it challenge to detect fossilization
- Multicellular animals with body cavities that are lined with mesoderm.
- Their digestive tract includes a mouth and an anus unlike Cnideria

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- Seisonidea
- Bdelloidea
- Monogononta (largest group)

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- Divided into four sections: head, neck, body, and foot
- Head supports tentacles called cilia, which propels water into the organism's mouth.
- Neck contains a throat-like tube that funnels water into stomach
- Rotifers have thin layers of clear skin, but may also have a hard shell called a lorica
- They're invertebrates, so they have no spine or skeletal structure to maintain their shape

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- Some look like squares, circles, and other shapes
-  Cells grow larger as the organism ages and don't increase in number
- Females are larger than males and are able to reproduce asexually without help from a mate
- They can still reproduce sexually during direct physical contact

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Cnidaria is one of the more primitive animal phyla. It includes aquatic organisms such as jellyfish, sea anemones, corals, and hydras. Most cnidarians are marine, although a few, such as the well-known hydra, are freshwater species.

Characteristics of Cnidarians

All cnidarians are characterized by radially symmetric body plans, rather than the bilaterally symmetric body plans that are found in most other animal phyla. Although cnidarians are more advanced than sponges (phylum Porifera) in that they possess distinct tissue layers, they lack many of the features of more advanced animal phyla, such as internal organs and central nervous systems. Most cnidarians possess tentacles, and many also have nematocysts (specialized stinging cells). Both are involved in feeding.

Cnidarians are characterized by the presence of three tissue layers, an outer protective epidermis, a middle layer called the mesoglea, and an inner layer called the gastrodermis, whose function is primarily digestive. The mesoglea of cnidarians is not as highly developed as the mesoderm of other animal groups, being primarily gelatinous with only a few fibrous or amoeba-like cells.

Cnidarians possess only one digestive opening, which serves as both the mouth and the anus. This opening is surrounded by tentacles and leads to an internal digestive cavity called the gastrovascular cavity .

Cnidarians feed using tentacles that are embedded with stinging nematocysts. The nematocysts are springing barbs with small hairlike triggers that are activated by contact with prey. Most nematocysts require stimulation in more than one sensory mode before they will fire. For example, a nematocyst may respond only if there is mechanical stimulation from physical contact with the prey as well as chemical stimulation signaling the presence of suitable prey. As nematocysts fire, barbs unfold and become embedded in the tissue of the prey. At the same time, the nematocysts inject the prey with an immobilizing toxin through a long hollow thread within the barb. Once the prey item has been captured and subdued, tentacles are used by the cnidarians to bring the prey item into the gastrovascular cavity. Within the gastrovascular cavity, the food item is broken into small particles by digestive enzymes secreted by gastrodermal cells lining the cavity. The minute particles are then taken in by the gastrodermal cells, and digestion is completed in digestive vacuoles (small cavities) within these cells. The indigestible remnants of the prey are expelled from the mouth of the gastrovascular cavity.

One hypothesis about the origin of nematocysts suggests that they were prokaryotic endosymbionts which lived within eukaryotic cells as mutualists (mutualisms are symbiotic relationships between individuals of two different species, in which members of both species derive benefits from the relationship), the same way organelles (specialized parts of cells) such as mitochondria and chloroplasts are believed to originate.

Unlike more advanced animal phyla, cnidarians lack a central nervous system. Instead, their nerves are organized in nerve nets that cover the entire body. Impulses spread slowly out from the point of stimulation along the nerve net. Some cnidarians, such as jellyfish, have more complicated arrangements of nerves that allow for more complex responses to stimuli as well as more effective patterns of movement.

Cnidarians also lack certain tissue types found in other animal phyla, such as true muscle cells. However, they do have fibers that can contract and therefore can be used in capturing prey and in moving about.

Major Groups of Cnidarians

Cnidarians are divided into three major classes. These are the Hydrozoa (hydras and other colony-forming species), the Scyphozoa (jellyfish), and the Anthozoa (sea anemones and corals).

Hydrozoa.

The best-known member of the Hydrozoa is the hydra, a freshwater species. However, the hydra is not a typical hydrozoan. For example, the hydra has only a polyp stage, for example, whereas most hydrozoans have a biphasic (two-stage) life cycle that alternates between a sedentary polyp stage and a mobile, bell-shaped medusa stage. The hydra is not strictly sedentary; it moves in a very unusual way, by turning somersaults. In addition, most hydrozoans are colonial, with each colony arising from the asexual budding of a single individual. Members of a hydrozoan colony have interconnected gastrovascular cavities, and the fluid in this cavity is circulated by cells with long, beating flagella . There is typically some degree of division of labor within the colony. Usually, there are feeding polyps, which possess tentacles and nematocysts (stinging cells), and reproductive polyps, which continually bud off tiny mobile medusas. The medusas swim by tightening and relaxing cells within the bell, and are also scattered by prevailing water currents. Medusas release sperm and eggs directly into the water, where fertilization occurs. The zygote (fertilized egg) develops into what is called a planula larva-the larvae of cnidarians. The larva ultimately settles to the substrate (rocky bottom of the ocean), finds something to anchor to, develops a mouth and tentacles, and becomes a polyp that subsequently buds to form a new colony.

Scyphozoa.

The Scyphozoa includes the well-known jellyfish. In this group, the polyp stage is far less significant than among the Hydrozoa, since the medusa stage is dominant. Scyphozoan medusas grow to sizes considerably larger than those found among the Hydrozoa. They range in size from a few centimeters to over 2 meters across. The nervous systems of jellyfish are also more developed than those of other cnidarians. Instead of a simple nerve net, they have a nerve ring around the edge of the bell portion of the medusa. Neurons throughout the rest of the body connect to this ring. This organization allows for faster conduction of impulses from one side of the body to the other, which in turn allows the jellyfish to swim with coordinated contractions of the entire bell.

Anthozoa.

The Anthozoa includes the sea anemones and the corals. These species lack the medusa stage altogether, and exist exclusively in the polyp form. Anthozoans tend to have more highly developed contractile cells (cells capable of contracting) than other cnidarians, as well as a more highly developed, thicker mesoglea, which often forms a fibrous connective tissue. Corals secrete a hard, limy skeleton and can form huge reefs, such as the Great Barrier Reef off the coast of Australia. Coral reefs are an impressive ecosystem, one of the most diverse and productive on Earth.

see also Phylogenetic Relationships of Major Groups.

Bibliography

Anderson, Donald Thomas. Atlas of Invertebrate Anatomy. Sydney, Australia: UNSW Press, 1996.

Barrington, Ernest James William. Invertebrate Structure and Function. New York: Wiley, 1979.

Chesher, Richard H. Living Corals. New York: C. N. Potter, 1979.

Clarkson, Euan Neilson Kerr. Invertebrate Paleontology and Evolution. Boston: G. Allen and Unwin, 1979.

Mayer, Alfred Goldsborough. Medusae of the World. Washington, D.C.: Carnegie Institution of Washington, 1910.

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Cnidaria is one of the more primitive animal phyla. It includes aquatic organisms such as jellyfish, sea anemones, corals, and hydras. Most cnidarians are marine, although a few, such as the well-known hydra, are freshwater species. All cnidarians are characterized by radially symmetric body plans, rather than the bilaterally symmetric body plans that are found in most other animal phyla.

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Phylum Cnidaria  - General Characteristics

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- The life cycle contains has two stages, sessile and

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- They use their tentacles with nematocysts to catch their prey. The nematocysts are sprining barbs with small hairlike triggers which are activated by contact with prey.
- Their mesoderm is pretty much all gelatinous.
- Polyp - They sit and wait for prey to come by (Hydras, Anemones)
- Medusa- Flattened mouth down versions and passively drifts with current (sea Jellies)

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- They have tentacles with stinging cells at the tips to capture prey
- They only have two basic body types
- Their middle layer isn't as developed as other phyla is
- They lack a nervous system and internal organs

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- Jellyfish
- Sea Anemones
- Corals
- Hydras
- They are grouped into hydrozoans, scyphozoans, and anthazoans.

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- Characterized by radially symmetric body plans
- They lack many of the features other more advanced phyla has, such as, internal organs and central organs.
- Most cniderians posses tentacles and some have specialized stinging cells called nematocysts.
- They posse three tissue layers, an outer protective epidermis, a middle layer called mesoglea, and an inner layer called the gastrodermis
-  The mesoglea only contains primarily gelatinous
- Cniderians have one digestive opening which serves as the mouth and as the anus
- Cniderians tentacles with stinging cells help them with eating.
- Carnivorous

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The Porifera are sponges. They are primarily marine animals. There are nine thousand species of sponges. There are following c haracteristics of the phylum Porifera:

1. Their bodies consist of loosely organized cells.

2. They vary in size from less than a centimeter to a mass that can fill your arm.

3. They are asymmetrical or radially symmetrical.

4. They have three cell types: pinacocytes, mesenchyma cells, and choanocytes.

5. They have central cavity or spongocoel. This cavity may be divided into series of branching chambers. Water circulates through these chambers for feeding.

6. Numerous pores are present in the body wall. i.e. ostia and osculum

7. They have no tissue or organ.

8. Skeleton is composed of spicules.

9. Nervous system is absent but neurosensory cells are present.

10. Asexual reproduction takes place by budding.

11. They are hermaphrodites and larvae are produced during development.

CELL TYPES, BODY WALL AND SKELETONS
Sponges have simple bodies. But still sponges are more than colonies of independent cells. The sponges also have specialized cells. Therefore, division of labour is present in them. Following types of cells are present in phylum porifera.

1. Pinacocytes: Pinacocytes are thin walled and flat cells. They line the outer surface of a sponge. Pinacocytes are slightly contractile. Their contraction can change the shape of some sponges. Some pinacocytes forms tube like contractile porocytes. Porocytes regulate water circulation. The openings of the porocytes are pathways tiw water movement of water through the body wall.

2. Mesohyl: Mesohyl is a jelly like layer present below the pinacocytes. Amoeboid cells are present in it. These cells are called mesenchyma cells. The meseuchyma cells freely move in the mesohyl. These cells are specialized for reproduction, secreting, skeletal elements, transporting and storing food and forming contractile rings around openings in the sponge wall.

3. Choanocytes: Choanocytes or collar cells are present below the mesohyl. They form the lining of the inner chamber. Choanocytes are flagellated cells. They have a collar like ring of microvilli surrounding a flagellum. Microfilaments connect the microvilli. It forms a netlike structure within the collar. The flagellum creates water currents through the sponge. The collar filters microscopic lbod particles from the water. Collar cells arc also present in a group of protists called choanollagellates. Choanocytes are present in sponges and choantlagellaes. It suggests an evolutionary link between these groups.

4. Skeleton: The nature of the skeleton is an important characteristic in sponge taxonomy. There are two types of skeleton in sponges:

(a) Spit lest The spicules consist of microscopic needlelike spikes Spic les are formed by amoeboid cells. They are made of calcium carbonate or silica. They have different shapes.

(I)) Spongin fibers: The spongin fibers are made up of . spongin. Spongin is a fibrous protein made of collagen. It is dried, beaten and washed and all cells are removed. This washed and dried spongin produce a commercial sponge.
WATER CURRENTS AND BODY FORMS (Water Canal System)
The lit of a sponge depends on the water currents. Thechoanocytes organized to form water canal system. Water currents bring food and oxygen for a sponge. It also carries away metabolic and digestive wastes. Water canal system is used for circulation and filtration of food. There are three principal types of water canal systems:

1. Ascon type

It is simplest and least common sponge body form. Ascon sponges are vase like. Ostia are the outer openings of porocytes. The porocytes open directly into spongocoel. Choanocytes line the spongocoel. The movements of flagella of choanocytes draw water into the spongocoel through the ostia. Water leaves the sponge through the osculum. Osculum is a single large opening at the top of the sponge.

2. Sycon type

The sponge wall is folded in the sycon body form. Following canals are formed by the folding of its wall:

(a) Incurrent canal: The invaginations of the body wall of sycon form incurrent canals. Water enters into incurrent canal through dermal pores.

(b) Radial canal: Pores in the wall of incurrent wall connect incurrent canals with radial canals. Choanoeytes line the radial canals. The beating of flagella of choanocytes moves water through incurrent radial canals and spongocoel. It finally moves out the osculum.

(c) Spongocoel: The radial canals lead to spongocoel.

Water path through sycon type: Dermal pore - incurrent canal - pore - radial canal - spongocoel - osculum.

3. Leucon type

Leucon sponges have an extensively branched canal system. There are following chambers in leucon type:

(a) Branched incurrent canal: Water enters the branched incurrent canals through ostia

(b Choanocytes chamber: Incurrent canal lead into choanocytes-lined chambers.

(c Excurrent canal: Choanocyte chamber open into the chambers of excurrent canals A large number of chambers and canals are present in leucon type. Therefore, spongocoel is absent in them. They have many oseulums for water leaving the sponge. Luecon type canal system is formed by the evolution of simple canal system.
Advantages of complex canal system
Complex sponges have an increased surface area for choanocytes. Therefore, a large amount of water through the sponge. It increases the filtering capability of sponges.
MAINTENANCE FUNCTIONS
1. Nutrition

Food: Sponges feed on particles with size from 0.1 to 50 pm. Their food consists of bacteria, microscopic algae, protists and other suspended organic matter. The preys are slowly drawn into the sponge and digested. Large populations of sponges play an important role in reducing the turbidity of coastal waters. A single leucon with size 1 cm in diameter and 10cm high can fitter 20 liters of water everyday.

A few species of sponges are carnivores. The deep-water sponges like Asbestopduma have spicules covered filaments. It captures small crustaceans with the help of these spiculces.

Mechanism of feeding: Choanocytes filter small suspended food particles. Water passes through their collar near the base of the cell. It then moves out of choanocytes into the sponge chamber through the open end of the collar. Suspended food is trapped on the collar. It passes through microvilli and reaches at the base of the collar. It forms a food vacuole in collar. The pH of food is changed. Digestion in food vacuole takes place by lysosomal enzymes. Partially digested food is passed into amoeboid cells. Amoeboid cells distribute it to other cells.

Pinacocyts lines the incurrent canal. Large food particles (up to 50 pm) can enter into pinacocytcs byphagocytosis. Sponges also absorb nutrients dissolved in seawater by active transport.

2. Excretion and respiration

There is an extensive canal system in sponges. A large volume of water circulates of through these canals. All sponge cells are in close contact with water. Thus, nitrogenous waste (principally ammonia) is removed and gas exchange occurs by diffusion.

3. Coordination

There are two forms of coordination in sponges:

(a) Coordination by external factors: Sponges do not have nerve cells to coordinate body functions. Mostly individual cells show response to a stimulus. For example, Light inhibits the constriction of porocytes and other cells surrounding the ostia. It keeps the incurrent canals open. Therefore, water circulation through some sponges is minimum at sunrise. But it is maximum just before sunset.

(b) Coordination by internal factors: Some other reactions suggest that some communication is present among cells. For example, the rate of water circulation through a sponge can drop suddenly without external cause. This reaction takes place due to choanocytes. It stops the activities simultaneously. These reaction shows that some form of internal communication is present in the sponges. The nature of this communication is unknown. Amoeboid cells may transmit chemical messages and ion movement over cell surfaces. It is a possible control mechanism.
REPRODUCTION
1. Sexual Reproduction

Most sponges are monoecious. But individual sponges produce eggs and sperm at different times. Therefore, they do not self-fertilized.

(a) Gametogensis: Certain choanocytes lose their collars and flagella. They undergo and form flagellated sperm. Other choanocytes (and amoeboid cells) undergo meiosis and form eggs.

(b) Fertilization: Eggs are retained in the mesohyl of the parent. Sperm cells passes from one sponge through the osculum and enter another sponge with the incurrent water. Sperm are trapped by choanocytes. Sperm is covered into a vacuole in choanocytes. The choanocytes lose their collar and flagellum and become amoeboid cells. It transports sperm into the eggs and zygote is formed.

(c) Development: Early development occurs in the mesohyl. Cleavage occurs in zygote. A flagellated larval stage is formed. These larvae may be parenchymula larva or amphiblastula larva. The larva becomes free. The water currents carry the larva out of the parent sponge. It freely swims for two days. Then the larva settles on the substrate and develops into the adult body form.

2. Asexual reproduction

(a) Gemmule formation: Asexual reproduction takes place by gemmules formation. Gemmule is a resistant capsule containing masses of amoeboid cells. The parent sponge dies in the winter and it releases gemmules. Gemmules can survive both in freezing and drying condition. The conditions become favorable in the spring. Now the ameboid cells come out through a tiny opening called the micropyle. It develops into a sponge.

(b) Regeneration: Some sponges possess great powers of regeneration. Portions of a sponge are cut or broken. The broken piece forms new sponge.

Similar Articles:

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Phylum Porifera - Characteristics , Types, Functions and Reproduction

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The Porifera are sponges. They are primarily marine animals. There are nine thousand species of sponges. There are following c haracteristics of the phylum Porifera: Their bodies consist of loosely organized cells. They vary in size from less than a centimeter to a mass that can fill your arm.

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Unique features of sponges - Queensland Museum

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Marine sponges of Queensland and tropical Australasia

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What Is a Poriferan?

Picture yourself scuba diving in a tropical paradise. Under the sea, beautiful fish swim through gardens of coral, and colorful tubes that look like plants sprout from the cracks. However, these tubes are actually animals called sea sponges, or poriferans.

Poriferans are stationary animals that live mostly in salt water and grow off of a rock substrate. Although poriferans all seem similar, once you dive into different parts of the ocean, you'll quickly realize that Porifera is quite a diverse group. With over 8,000 species occurring in colors of the entire spectrum, and sizes ranging from under one inch to over ten feet, poriferans are quite complex. Today, we'll look at the three types of poriferans and some interesting examples of each. Let's start with asconoid.

Asconoid

Sea sponges are classified into three types based on their body plan, or how their cells are organized. The asconoid sponge is the simplest type of sponge, and it has a body with radial symmetry, meaning it looks the same on all sides. Water flows into the sponge through pores on the surface to the atrium, which is a central cavity. Think of each pore like a tiny road into the town, or atrium. Inside the sponge, tiny cells called choanocytes use flagella to create a current. As water flows through the sponge, microscopic prey is captured as food. Water then flows out of the osculum, a central hole at the top.

Syconoid

Now let's talk about syconoid sponges, which get a little more complex. Syconoid sponges have thicker walls and a more complex series of canals that allow for water flow. Instead of the tiny, straight roads that the asconoid sponges have, these sponges have roads with intersections. The in-current canals that allow water to flow into the atrium have branches, and can be complex, with many types of cells participating in water movement. The water flows into the atrium through these many roads, but still goes out only one opening, the osculum. Some syconoid sponges have radial symmetry as well, but many have an irregular shape.

Leuconoid

Now we come to the leuconoid variety. Leuconoid sponges are the largest sea sponges and have evolved in current canals of even greater complexity in order to support their large bodies. Being more complicated than syconoid sponges, they lack radial symmetry and often take on irregular shapes. The water canals are branched like the syconoid sponges, but only some canals have flagella, enabling the sponge to control which way water flows into the atrium. The top of this sponge also has multiple oscula, further complicating the water flow pattern. This allows the sponge to grow larger because it can distribute oxygen and nutrients more efficiently to its cells. Using our road analogy, this sponge has many intersections, like the syconoid sponge, but there are different speed limits on the road, allowing the traffic to move more directly to the town, or atrium, in some areas.

Species of Sponges

Now that we've discussed the three major types of poriferans, let's explore some of the species of Porifera. Clathrinida is a family of calcareous sponges. They are among the most primitive sponges, belonging to the asconoid type. They are found along rocky coasts in temperate waters. With a skeleton made entirely of calcium carbonate, these sponges appear as small, porous tubes.

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porifera: species & types - video & lesson transcript | study.com

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Porifera: Species & Types - Video & Lesson Transcript | Study.com

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Picture yourself scuba diving in a tropical paradise. Under the sea, beautiful fish swim through gardens of coral, and colorful tubes that look like plants sprout from the cracks. However, these tubes are actually animals called sea sponges, or poriferans. Poriferans are stationary animals that live mostly in salt water and grow off of a rock substrate.

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Simple Animals: Sponges, Jellies, & Octopuses - Crash Course Biology #22

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Hank introduces us to the "simplest" of the animals, complexity-wise: beginning with sponges (whose very inclusion in the list as "animals" has been called into question because they are so simple) and finishing with the most complex molluscs, octopuses and squid. We differentiate them by the number of tissue layers they have, and by the complexity of those layers.

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- They feel no pain because of their lack of a nervous system
- They can regenerate in response to their environment. They can rebuild lost cells
-  No tissues nor organs
- They eat by spongocoel

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- No mouth,  Feeds through spongocoel
- Their bodies lack true tissues and organs
- No nervous system, (feels no pain)
-  There Plasticity. They are able regenerate in reaction to the environment.

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- Asconoid
- Syconoid
- Leuconoid

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- Doesn't have any body symmetry (asymmetrical)
- Their bodies contain loosely organised cells
- They contain no tissue or organs
- Porifera reproduce through asexual reproduction by budding
- No nervous system, but neurosensory cells are present
- They are hermaphrodites and larvae are produced throughout development
- Skeleton is built out of spicules
- A plethora of pores are found on their body wall
- They have spongocoel. This cavity divides into a variety of branching chambers. Through these chambers water flows for feeding.
- Choanocytes creates the water current.