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Member of the phylum Arthropoda and in the class Insecta

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Introduction: Insects are arthropods with jointed appendages, segmented bodies, and an exoskeleton composed of chitin. Insects are in the class Insecta, & are the largest and most diverse group of animals on earth. The genus Romalea is a large grasshopper common in the southeastern United States. Insects have three body regions (head, thorax, & abdomen), 3 pairs of legs attached to the thorax, a single pair of antenna attached to the head, mouthparts adapted for chewing or sucking, and two pairs of wings. Some insects may have a single pair of wings or be wingless. Insect legs are often adapted for digging, crawling, jumping, or swimming. The insects are mostly terrestrial, they breathe air which enters small lateral openings on the body called spiracles and circulates in a system of ducts to all organs and tissues. Their chewing or sucking mouth parts are adapted for feeding on plant or animal materials. Classification: Objective: Identify & label the internal & external anatomy of a grasshopper. Materials: Lab apron, gloves, eyeglasses, dissecting pan, dissecting kit with forceps & scalpel, t-pins, magnifying glass, preserved grasshopper, paper, pencil.
Procedure (External Anatomy): Examine the entire grasshopper and identify the major subdivisions and parts of the body.

Obtain a preserved grasshopper & rinse off any preservative with water. Place grasshopper in the dissecting pan.

1. Observe that the body of the grasshopper is divided into 3 regions - the head, the thorax, and abdomen. Label these on Figure 2.

2. Examine the head and locate the following parts:
HEAD
Antennae (two, slender appendages)
Compound eyes (2, large lateral)
Ocelli (or simple eyes) - 3, small, between compound eyes
Mouth parts - Labrum (upper lip), mandibles (jaws) below the labrum, maxillae located behind the mandibles to help cut & hold food, and the lower lip or labium

1. Label the mouthparts, eyes, and antenna on Figure 1.

2. Using forceps, remove each of the appendages from the head, and attached them to table 1.

3. Examine the following appendages on the thorax (middle section of the grasshopper's body):

THORAX
Legs (first 2 pairs are for walking & the last pair are for jumping)
Wings (forewings have a leathery appearance & protect the hind wings)

1. Using forceps, remove one of the walking legs and identify these parts - the coxa connects the femur (the thickest part of the leg) to the grasshopper's body; a slender, spiny tibia connects the femur to the tarsal segments (lowest part of the leg). Label these on Figure 2.

2. Remove a jumping leg and attach the walking leg & jumping leg to Table 1.

3. Raise both pairs of wings and locate the first abdominal segment.

4. Locate the tympanic membrane or eardrum on the first abdominal segment. Label this on Figure 2.

1. Using a magnifying glass, locate the spiracles or tiny pores for respiration on each side of the abdominal segments. Label these on Figure 2.

2. Determine if your grasshopper is a male or female by looking at the end of the abdomen. Females have a tapered abdomen that ends in a pointed egg laying tube called the ovipositor. Male have a more rounded abdomen that turns upward.

ABDOMEN
Spiracles (small openings on the side of somites or body segments)
Auditory Organs (two located laterally on the 1st body somite or segment)
Ovipositor (on female)
Observations & Conclusion: Figure 1 - Grasshopper Head (Label ALL parts.) Figure 2 - External Grasshopper anatomy (Label ALL parts.) Table 1 - External Appendages of the Grasshopper (Attach ALL parts.) 1. Which region of the insect's body is specialized for sensory functions? Explain your answer. 2. Which region of the insect's body is specialized for movement & explain why? 3. What is the purpose of compound eyes? of simple eyes? 4. List the grasshopper's mouthparts & their functions. 5. How are the ends of the legs adapted for holding onto plants? 6. How is the third pair of legs adapted for jumping? 7. Describe the differences between the two pairs of wings (appearance & function). 8. How does the tympanic membrane help a grasshopper? 9. What system do spiracles open into on a grasshopper? 10. Do all abdominal segments have spiracles? Are there any spiracles on the thoraic segments? 11. How did you determine the sex of your grasshopper? 12. Explain how grasshoppers dig holes to lay their eggs.

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grasshopper dissection - Biology Junction

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Grasshopper Dissection Introduction: Insects are arthropods with jointed appendages, segmented bodies, and an exoskeleton composed of chitin. Insects are in the class Insecta, & are the largest and most diverse group of animals on earth. The genus Romalea is a large grasshopper common in the southeastern United States.

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Member of the Arthropoda phylum and in the Crustaceans class

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Crayfish Dissection

Objectives:
* Describe the appearance of various organs found in a crayfish.
* Name the organs that make up systems of the crayfish.

Materials:
* safety goggles, gloves, magnifying glass, a lab apron, plastic zip lock bag preserved crayfish, pen, dissecting tray, paper towels, scissors, forceps, dissecting needle, and dissecting pins.

Purpose:
In this lab, you will observe the external structures of a crayfish and dissect it to study its internal structures and systems.

Background:
Like all crustaceans, a crayfish has a fairly hard exoskeleton that covers its body. As shown in the diagram on the next page, its body is divided into two main parts, the cephalothorax and the abdomen. The cephalothorax consists of the cephalic (or head) region and the thoracic region. The part of the exoskeleton that covers the cephalothorax is called the carapace. The abdomen is located behind the cephalothorax and consists of six clearly divided segments. The cephalothorax consists of 13 segments. Each segment of both the cephalothorax and the abdomen contains a pair of appendages. The head (or cephalic) region has five pairs of appendages. The antennules are organs of balance, touch, and taste. Long antennae are organs for touch, taste, and smell. The mandibles, or jaws, crush food by moving from side to side. Two pairs of maxillae hold solid food, tear it, and pass it to the mouth. The second pair of maxillae also helps to draw water over the gills. Of the eight pairs of appendages on the cephalothorax, the first three are maxillipeds, which hold food during eating. The chelipeds are the large claws that the crayfish uses for defense and to capture prey. Each of the four remaining segments contains a pair of walking legs. In the abdomen, the first five segments each have a pair of swimmerets, which create water currents and function in reproduction. The sixth segment contains a modified pair of uropods. In the middle of the uropods is a structure called the telson, which bears the anus. The uropod and telson together make up the tail fan. The crayfish moves backward by forcing water forward with its tail fan.
Procedure Part 1-External Anatomy of a Crayfish
1. Put on safety goggles, gloves, and a lab apron.

2. Place a crayfish on its side in a dissection tray. Use the diagram below to locate the cephalothorax and the abdomen. The carapace, a shield of chitin, covers the dorsal surface of the cephalothorax. On the carapace, observe an indentation, the cervical groove, that extends across the midregion and separates the head and thoracic regions. On the thoracic region, locate the prominent suture or indentation on the cephalothorax that defines a central area separate from the sides. Note the individual segments of the abdomen.
What is the main difference between the cephalothorax and abdomen? ___________________________________________________________
3. Turn the crayfish with its DORSAL side upward, and locate the rostrum, which is the pointed extension of the carapace at the head of the animal shown in the diagram above. Beneath the rostrum locate the two eyes. Notice that each eye is at the end of a stalk.

4. Locate the five pairs of appendages on the head region. First locate the antennules in the most anterior segment. Behind them observe the much longer pair of antennae.
Why is it useful to view the specimen on its Dorsal side for this part of your study?
______________________________________________________________
5. Locate the mouth. Then observe the mandibles, or true jaws, behind the antennae. Now locate the two pairs of maxillae, which are the last appendages in the cephalic region.
Which appendages in the cephalic region are related to the eating of food?
_____________________________________________________________
6. On the thoracic portion of the cephalothorax, observe the three pointed maxillipeds.
How are the maxillipeds related to eating?
______________________________________________________________
7. Next observe the largest prominent pair of appendages, the chelipeds, or claws. Behind the chelipeds locate the four pairs of walking legs, one pair on each segment.

8. Now use the walking legs to determine the sex of your specimen. Locate the base segment of each pair of walking legs. The base segment is where the leg attaches to the body. Use a magnifying glass to study the inside surface of the base segment of the third pair of walking legs. If you observe a crescent-shaped slit, you have located a genital pore of a female. In a male, the sperm duct openings are on the base segment of the fourth pair of walking legs. Use a magnifying glass to observe the opening of a genital pore.
Is your specimen a male or a female?
_____________________________________________________________
Exchange your specimen with a nearby classmate who has a crayfish of the opposite sex. Then study its genital pores.

9. On the abdomen, observe the six distinct segments. On each of the first five segments, observe a pair of swimmerets.

10. On the last abdominal segment, observe a pair of pointed appendages modified into a pair of uropods. In the middle of the uropods, locate the triangular-shaped telson.

11. Now turn the crayfish ventral side up. Observe the location of each pair of appendages from the ventral side.
From which view, dorsal or ventral, can you see the location of the appendages on the segments more clearly?
______________________________________________________________
12. Remove all jointed appendages of the crayfish and attach them to the table on the crayfish worksheet.
If dissection is two day, complete steps 13 and 14 only!
13. Next you will study the internal anatomy of a crayfish. If you must store your specimen until the next lab period, cover it with a dampened paper towel. Then place the specimen on the tray in a plastic bag. Close the bag with a twist tie. Write your name on the bag with a felt-tip marking pen, and give your specimen to your teacher.

14. Clean up your work area and wash your hands before leaving the lab.

Part 2-Internal Anatomy of a Crayfish

15. Put on a lab apron, gloves, and safety goggles.

16. Using one hand to hold the crayfish dorsal side up in the dissecting tray, use scissors to carefully cut through the back of the carapace along dissection cut line 1, as shown in the diagram below. Cut along the indentations that separate the thoracic portion of the carapace into three regions. Start the cut at the posterior edges of the carapace, and extend it along both sides in the cephalic region.

17. Use forceps to carefully lift away the carapace. Be careful not to pull the carapace away too quickly. Such action would disturb or tear the underlying structures.

18. Place the specimen on its side, with the head facing left, as shown in the diagram below. Using scissors, start cutting at the base of cut line 1. Cut along the side of the crayfish, as illustrated by cut line 2. Extend the cut line forward toward the rostrum (at the top of the head).

19. Use forceps to carefully lift away the remaining parts of the carapace, exposing the underlying gills and other organs.

20. Use the diagram below to locate and identify the organs of the digestive system. Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. Locate the digestive gland, which produces digestive substances and from which the absorption of nutrients occurs. Undigested material passes into the intestine. Observe that the intestine is attached to the lobed stomach. The undigested material is eliminated from the anus.
Rows of chitinous teeth line the stomach. Predict their function.
_____________________________________________________________
21. Use the diagram below to locate and identify the organs of the respiratory system. Locate the gills, which are featherlike structures found underneath the carapace and attached to the chelipeds and walking legs. A constant flow of blood to the gills releases carbon dioxide and picks up oxygen.
The feathery nature of the gills gives them a very large surface area. Why is this important?
____________________________________________________________
22. Use the diagram of the internal anatomy of the crayfish to locate and identify the organs of the circulatory system. Locate the dorsal tubular heart and several arteries. The crayfish has an open circulatory system in which the blood flows from arteries into sinuses, or spaces, in tissues. The blood flows over the gills before returning to the heart.

23. Use the same diagram to locate and identify the organs of the nervous system. Find the ventral nerve cord. Locate a ganglion, one of the enlargements of the ventral nerve cord. Locate the dorsal brain, which is located just behind the compound eyes. Note the two large nerves that lead from the brain, around the esophagus, and join the ventral nerve cord.
Many nerves leave from each ganglion. Where do you think these nerves go?
__________________________________________________________
24. Use the same diagram to locate and identify the organs of the excretory system. The blood carries cellular wastes to the disk-like green glands. Locate these organs just in front of the stomach. The green glands excrete waste through pores at the base of each antenna.
What organs in your body carry out the same function as the green glands? ____________________________________________________________
25. Use the diagram once again to locate and identify the organs of the reproductive system. The animal shown in the diagram is a male crayfish. If your specimen is a male, locate the testis. The testis is the long, white organ under the heart and a bit forward. The sperm ducts that carry sperm from the testis open at the fifth walking leg. If your specimen is a female, locate the bi-lobed ovary. It is in the same relative position as the testis, but the ovary appears as a large, reddish mass under the heart. Then locate the short oviducts that extend from near the center of each side of the ovary and open at the third walking leg. Exchange your specimen with a nearby classmate who has a crayfish of the opposite sex. Then study its reproductive system.

25. Dispose of your materials according to the directions from your teacher.

26. Clean up your work area and wash your hands before leaving lab.
BACK

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Crayfish Dissection Objectives: * Describe the appearance of various organs found in a crayfish. * Name the organs that make up systems of the crayfish. Materials: * safety goggles, gloves, magnifying glass, a lab apron, plastic zip lock bag preserved crayfish, pen, dissecting tray, paper towels, scissors, forceps, dissecting needle, and dissecting pins.

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Step by step directions with pictures....

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How to Dissect a Squid. The squid is a highly developed invertebrate that is classified as a cephalopod. Cephalopod means "head-footed" and was so-named because of the squid's body type with the head being directly attached to the feet...

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Squid Dissection Flashcards

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vocabulary from our squid lab Learn with flashcards, games, and more — for free.

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Unusual Mollusca

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Detailed walk-through of dissection with discussion and analysis.

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Detailed Sea Star (starfish) Dissection: Part I (Jr. High, High School and College Review)

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Part I - Sea star dissection for educational use: additional video, lesson plans, quizzes, additional dissections and more available at http://sdpb.sd.gov/oldschoolscience/dissection.aspx. The video details the external anatomy of a sea star.

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Note the organ systems of this member of the Echinodermata phylum.

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E chinoderms are radially symmetrical animals that are only found in the sea (there are none on land or in fresh water). Echinoderms mean "spiny skin" in Greek. Many, but not all, echinoderms have spiny skin. There are over 6,000 species. Echinoderms usually have five appendages (arms or rays), but there are some exceptions.

Radial symmetry means that the body is a hub, like a bicycle wheel, and tentacles are spokes coming out of it (think of a starfish). As larvae, echinoderms are bilaterally symmetrical. As they mature, they become radially symmetrical.

Most adult echinoderms live on the bottom of the ocean floor. Many echinoderms have suckers on the ends of their feet that are used to capture and hold prey, and to hold onto rocks in a swift current.

Sea Stars
Sea stars (group name Stelleroidea) are sometimes called starfish, though they are not real fish (they lack both vertebrae and fins). There are two sub-types of sea stars:

Asteroideas are the true sea stars and sun stars.

Ophiuroideas are brittle stars and basket stars.

The differences between the two sub-types lies in how the arms connect to the central disk. Ophiuroids have arms that do not connect with each other. There is a distinct boundary between arm and central disk. Asteroids have arms that are connected to each other. Also, it is harder to tell with asteroids where the central disk ends and the arms begin.

The sea star's top surface (or skin) looks spiny if you examine it. If you look very closely you will notice that there are different types of growths on the surface. Some bumps are used to absorb oxygen, they are called dermal branchiae. Pedicellaria are pincher-like organs used to clean the surface of the skin. Barnacle larvae could land on a sea star and start growing if it were not for these organs.

How Do Sea Stars Move?
Each sea star had hundreds of tiny feet on the bottom of each ray. These are tube feet, or podia. These tiny feet can be filled with sea water. The vascular system of the sea star is also filled with sea water. By moving water from the vascular system into the tiny feet, the sea star can make a foot move by expanding it. This is how sea stars move around. Muscles within the feet are used to retract them.

Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going.

Can Sea Stars Grow New Arms?
Given enough time, sea stars can grow back arms that have been damaged or removed. For a few species, the severed arm can grow back into a complete sea star! For most sea stars, however, a severed limb dies.

What Do Sea Stars Eat?
Sea stars eat many things. A sea star's diet can include: barnacles, snails, sea urchins, clams, and mussels. A few species, such as the spiny star of the North Atlantic, eat other sea stars! Many sea stars eat mussels and clams in an interesting way. They surround the shell and use the suckers on their feet to pull the two shells (or valves) apart. The sea star has enough force in its arms to actually bend the shell! This creates an opening between the two shells that is only .01 inches wide. Using this tiny gap, the sea star puts its stomach into the clam's shell and eats its insides. When it is done, nothing is left but an empty shell.
Materials:
Preserved starfish, dissecting pan, scissors, scalpel, forceps, T-pins, pencil, lab apron, safety glasses
Procedure:
Dorsal view of starfish showing external anatomy

Ventral view of starfish showing external anatomy

Dorsal view of a dissected starfish showing rectal cecum, anus, madreporite, pyloric stomach, pyloric duct

Dorsal view of a dissected starfish showing madreporite, stone canal, cardiac stomach, and ampullae

Dissection showing where cardiac stomach opens into the mouth

Close up of madreporite and stone canal

Dorsal view of a dissected starfish showing pyloric caecum and pyloric ducts

Dorsal view of a dissected starfish showing gonads and ampullae

Ventral view of starfish showing external anatomy

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Starfish Dissection Introduction: Echinoderms are radially symmetrical animals that are only found in the sea (there are none on land or in fresh water). Echinoderms mean "spiny skin" in Greek. Many, but not all, echinoderms have spiny skin. There are over 6,000 species. Echinoderms usually have five appendages (arms...

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Detailed walk-through of dissection with analysis.

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Detailed Clam (bivalve, molluscs or mollusks) Dissection (Jr. High, High School and College Review)

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This organism belongs to the phylum Mollusca

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Clam Dissection

Introduction
The phylum Mollusca includes snails, clams, chitons, slugs, limpets, octopi, and squid. As mollusks develop from a fertilized egg to an adult, most pass through a larval stage called the trocophore. The trocophore is a ciliated, free-swimming stage. Mollusks also have a radula or file-like organ for feeding, a mantle that may secrete a shell, and a muscular foot for locomotion. Clams are marine mollusks with two valves or shells. Like all mollusks, a clam has a mantle which surrounds its soft body. It also has a muscular foot which enables the clam to burrow itself in mud or sand. The soft tissue above the foot is called the visceral mass and contains the clam's body organs.
Procedure Figure 1
Objective
To study the internal and external anatomy of a bivalve mollusk.

Materials
Dissecting pan, dissecting kit, screwdriver, lab apron, plastic gloves, safety glasses, preserved clam

1. Put on your lab apron, safety glasses, and plastic gloves.

2. Place a clam in a dissecting tray and identify the anterior and posterior ends of the clam as well as the dorsal, ventral, & lateral surfaces. Figure 1

Locate the umbo, the bump at the anterior end of the valve. This is the oldest part of the clam shell. Find the hinge ligament which hinges the valves together and observe the growth rings.

Turn the calm with its dorsal side down and insert a screwdriver between the ventral edges of the valves. Carefully work the tip of the screwdriver between the valves so you do not jab your hand.
Figure 2

1. Turn the screwdriver so that the valves are about a centimeter apart. Leave the tip of the screwdriver between the valves and place the clam in the pan with the left valve up.

2. Locate the adductor muscles. With your blade pointing toward the dorsal edge, slide your scalpel between the upper valve & the top tissue layer. Cut down through the anterior adductor muscle, cutting as close to the shell as possible.

Repeat step 6 in cutting the posterior adductor muscle. Figure 2

1. Bend the left valve back so it lies flat in the tray.

2. Run your fingers along the outside and the inside of the left valve and compare the texture of the two surfaces.

1. Examine the inner dorsal edges of both valves near the umbo and locate the toothlike projections. Close the valves & notice how the toothlike projections interlock.

2. Locate the muscle "scars" on the inner surface of the left valve. The adductor muscles were attached here to hold the clam closed.

3. Identify the mantle, the tissue that lines both valves & covers the soft body of the clam. Find the mantle cavity, the space inside the mantle.

Locate two openings on the posterior end of the clam. The more ventral opening is the incurrent siphon that carries water into the clam and the more dorsal opening is the excurrent siphon where wastes & water leave.
Figure 3

1. With scissors, carefully cut away the half of the mantle that lined the left valve. After removing this part of the mantle, you can see the gills, respiratory structures.

2. Observe the muscular foot of the clam, which is ventral to the gills. Note the hatchet shape of the foot used to burrow into mud or sand.

Locate the palps, flaplike structures that surround & guide food into the clam's mouth. The palps are anterior to the gills & ventral to the anterior adductor muscle. Beneath the palps, find the mouth.

1. With scissors, cut off the ventral portion of the foot. Use the scalpel to carefully cut the muscle at the top of the foot into right and left halves.

2. Carefully peel away the muscle layer to view the internal organs.

1. Locate the spongy, yellowish reproductive organs.

2. Ventral to the umbo, find the digestive gland, a greenish structure that surrounds the stomach.

3. Locate the long, coiled intestine extending from the stomach.

4. Follow the intestine through the calm. Find the area near the dorsal surface that the intestine passes through called the pericardial area. Find the clam's heart in this area.

1. Continue following the intestine toward the posterior end of the clam. Find the anus just behind the posterior adductor muscle.

2. Use your probe to trace the path of food & wastes from the incurrent siphon through the clam to the excurrent siphon.

3. Answer the questions on your lab report & label the diagrams of the internal structures of the clam. Also, use arrows on the clam diagram to trace the pathway of food as it travels to the clam's stomach. Continue the arrows showing wastes leaving through the anus.

When you have finished dissecting the clam, dispose of the clam as your teacher advises and clean, dry, and return all dissecting equipment to the lab cart. Wash your hands thoroughly with soap.

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Clam Dissection Introduction The phylum Mollusca includes snails, clams, chitons, slugs, limpets, octopi, and squid. As mollusks develop from a fertilized egg to an adult, most pass through a larval stage called the trocophore. The trocophore is a ciliated, free-swimming stage. Mollusks also have a radula or file-like organ for feeding, a mantle that may ...

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Detailed walk-through of dissection with analysis.

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Dissection 101 | Detailed Earthworm Dissection Video

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This video details the external and internal anatomy of an earthworm.

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Go through the steps of the earthworm's dissection.
Identify all the organs and make comparisons to our own anatomy.

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Earthworm Dissection
Pictures: Modern Biology, Holt The following is a classification of a species in the earthworm family Lumbricidae. This common species is Lumbricus terrestris also known as the night crawler or dew worm. Objectives:
* Describe the appearance of various organs found in the earthworm.
* Name the organs that make up various systems of the earthworm. Materials:
Safety goggles, dissecting pins, gloves, forceps, lab apron, scissors, paper towel, scalpel, water, dissecting probe, preserved earthworm, hand lens, dissection tray. Purpose:
In this lab, you will dissect an earthworm in order to observe the external and internal structures of earthworm anatomy. Background:
Among the most familiar invertebrate animals are the earthworms, members of the phylum Annelida. The word annelida means "ringed" and refers to a series of rings or segments that make up the bodies of the members of this phylum. Internally, septa, or dividing walls, are located between the segments. External segments are called metameres. There may be more than 100 segments in an adult worm. The clitellum is a swelling of the body found in sexually mature worms and is active in the formation of an egg capsule, or cocoon. Eggs are produced in the ovaries and pass out of the body through female genital pores. Sperm are produced in the testes and pass out through tiny male genital pores. During mating, sperm from one worm travel along the sperm grooves to the seminal receptacles of another worm. Fertilization of the eggs takes place outside the body as the cocoon moves forward over the body, picking up the eggs of one worm and the sperm of its mate. The pumping organs of the circulatory system are five aortic arches. Circulatory fluids travel from the arches through the ventral blood vessel to capillary beds in the body. The fluids then collect in the dorsal blood vessel and reenter the aortic arches. The earthworm takes in a mixture of soil and organic matter through its mouth, which is the beginning of the digestive tract. The mixture enters the pharynx, which is located in segments 1-6. The esophagus, in segments 6-13, acts as a passageway between the pharynx and the crop. The crop stores food temporarily. The mixture that the earthworm ingests is ground up in the gizzard. In the intestine, which extends over two-thirds of the body length, digestion and absorption take place. Soil particles and undigested organic matter pass out of the worm through the rectum and anus. The nervous system consists of the ventral nerve cord, which travels the length of the worm on the ventral side, and a series of ganglia, which are masses of tissue containing many nerve cells. The nerve collar surrounds the pharynx and consists of ganglia above and below the pharynx. Nervous impulses are responsible for movement and responses to stimuli. Each segment contains an enlargement, or ganglion, along the ventral nerve cord. Excretory functions are carried on by nephridia, which are found in pairs in each body segment. They appear as tiny white fibers on the dorsal body wall. The earthworm has no gills or lungs. Gases are exchanged between the circulatory system and the environment through the moist skin.
Procedure:

External Anatomy
1. Put on safety goggles, gloves, and a lab apron.
2. Place earthworm in the dissecting tray & rinse off the excess preservative. Identify the dorsal side, which is the worm's rounded top, and the ventral side, which is its flattened bottom. Turn the worm ventral side up, as shown in the diagram below. 3. Use a hand lens as you observe all parts of the worm, externally and internally. Locate the conspicuous clitellum, a saddle-like swelling on the dorsal surface. The clitellum produces a mucus sheath used to surround the worms during mating and is responsible for making the cocoon within which fertilized eggs are deposited. The anterior of the animal is more cylindrical than the flattened posterior and is the closest to the clitellum. The ventral surface of the earthworm is usually a lighter colour than the dorsal surface. The mouth is located on the ventral surface of the first segment while the anus is found at the end of the last segment. Find the anterior end by locating the prostomium (lip), which is a fleshy lobe that extends over the mouth. The other end of the worm's body is the posterior end, where the anus is located. 4. Locate the clitellum, which extends from segment 33 to segment 37. Look for the worm's setae, which are the minute bristle-like spines located on every segment except the first and last one. Run your fingers over the ventral surface of the earthworm's body. You should be able to feel bristle-like setae used for locomotion
5. Refer again to the diagram of the ventral view of the worm to locate and identify the external parts of its reproductive system. Find the pair of sperm grooves that extend from the clitellum to about segment 15, where one pair of male genital pores is located. Look also for one pair of female genital pores on segment 14. There is another pair of male genital pores on about segment 26. Try to find the two pairs of openings of the seminal receptacles on segment 10. Note: These openings are not easy to see.
Internal Anatomy Hint: Position your preserved earthworm dorsal side up and pin it down through the first segment and then again further back behind the clitellum. Cut a slit in the dorsal surface near the posterior pin. Using fine scissors extend the cut forward to the first segment. Be careful not to cut too deep. Starting at the first segment, cut the septa (thin membranes) that internally divide the segments, so the skin can be laid flat. Use additional pins to hold the integument open and expose the organs. Continue to lay the skin back until you have uncovered a centimeter or so of the intestine.
6. Turn the worm dorsal side up. Using a scalpel and scissors, make a shallow incision in the dorsal side of the clitellum at segment 33. CAUTION: Scalpels and scissors are very sharp. Report any cuts to your teacher. Using the forceps and scalpel, spread the incision open, little by little. Separate each septum from the central tube using a dissecting needle, and pin down each loosened bit of skin. Continue the incision forward to segment 1.

7. Use the diagram below to locate and identify the five pairs of aortic arches, or hearts. Then find the dorsal blood vessel. Look for smaller blood vessels that branch from the dorsal blood vessel.
Digestive System The earthworm is an example of a foraging herbivorous annelid, obtaining food by eating its way through the soil and extracting nutrients from the soil as it passes through the digestive tract. Hint: Starting at the anterior end, locate the muscular pharynx (food ingestion). This is followed by a tube-like esophagus which terminates in a crop (the wider organ) which serves as a storage stomach. Posterior to the crop you will find the gizzard. Gently press on the crop and gizzard to test their firmness. While the crop is soft and thin, the gizzard is muscular (soil is ground up and churned within the gizzard). The gizzard is followed by a long intestine in which both digestion and absorption occur. Undigested material is voided through the anus.
8. Locate the digestive tract, which lies below the dorsal blood vessel. Refer to the diagram above to locate the pharynx, esophagus, crop, gizzard, and intestine.

9. To find organs of the nervous system, push aside the digestive and circulatory system organs. Use the diagram below to locate the ventral nerve cord. Trace the nerve cord forward to the nerve collar, which circles the pharynx. Find one pair of ganglia under the pharynx and another pair of ganglia above the pharynx. The ganglia above the pharynx serve as the brain of the earthworm.

10. The worm's excretory organs are tiny nephridia. There are two in every segment. Use the preceding diagram to locate some nephridia.

11. Use the diagram below to locate and identify a pair of ovaries in segment 13. Look for two pairs of tiny testes in segments 10 and 11. To find these organs, you will again have to push aside some parts already dissected.

12. Dispose of your materials according to the directions from your teacher.

13. Clean up your work area and wash your hands before leaving the lab.

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Earthworm Dissection Pictures: Modern Biology, Holt The following is a classification of a species in the earthworm family Lumbricidae. This common species is Lumbricus terrestris also known as the night crawler or dew worm. Phylum - Class - Family - Genus - Species - Annelida Oligochaeta Lumbricidae Lumbricus terrestris Objectives: * Describe the appearance of ...