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BIO170 General Biology Freeman/Mac Leod FMCC
PROTOSTOMES: ECDYSOZOA
AND
DEUTEROSTOMES
Objective: After completing this exercise, you should be able to do the following:
 Describe features of the Ecdysozoa phyla: Nematoda and Arthropoda.
 Describe features of the Deuterostome phylum: Echinodermata
 Compare the anatomy of the representative animals describing similarities and
differences in organs and body form that allow the animal to carry out body functions.
 Discuss the relationship between body form and the lifestyle or niche of the organism.
Introduction
In this lab exercise you will study examples of two protostomes phyla included in the lineage
Ecdysozoa: Nematoda and Arthropoda. These organisms have coverings in their body surface
(exoskeleton) that they shed as they grow, a process called molting (ecdysis). In addition, you
will study one deuterostome phylum: Echinodermata
A. PHYLUM NEMATODA – ROUNDWORMS
Free-living nematodes are extremely abundant in soils and sediments where they feed on bacteria
and detritus. Other nematodes are plant parasites and may cause disease in economically
important crops. Still others parasitize animals (including humans). Well-known parasitic
nematodes include hookworms, pinworms, Guinea worm (Dracunculus), and intestinal
roundworms (Ascaris).
The body of a nematode is long, narrow and round; resembling a tiny thread in many cases. The
word "nematode" comes from a Greek word nema that means "thread". Nematodes are
bilaterally symmetrical, worm-like organisms that are surrounded by a strong, flexible noncellular layer called a cuticle. The cuticle is a feature shared with arthropods and other
ecdysozoans. As in those other groups, the cuticle is periodically shed during the life of a
nematode as it grows (usually four times) before reaching the adult stage. The cuticle is the
closest thing a roundworm has to a skeleton. In fact, the worm uses its cuticle as a support and
leverage point for movement. Near the body wall but under the epidermal cells are longitudinal
muscles; they run along the length of the body. A true coelom is lacking, instead, nematodes
have a pseudocoelom. The cavity of the pseudocoelom is small, being mostly filled with an
intestine and oviducts or testes. The space in the pseudocoelom is filled with body fluid which
exerts pressure on the cuticle. This hydrostatic skeleton gives the muscles of the animal
something to work against. The pressure also causes the intestine to be flattened. A simple
nervous system consists of a ring of nervous tissue around the pharynx that gives rise to dorsal
and ventral nerve cords running the length of the body (Figure 1).
Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is
high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and
forth. No cilia or flagella are present.
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BIO170 General Biology Freeman/Mac Leod FMCC
Nematodes excrete nitrogenous
waste using specialized cells or
structures called lateral lines
(excretory canal in the figure to
the left).
Reproduction is sexual.
Fertilization takes place when
males use special copulatory
spines to open the female’s
reproductive tract and inject
sperm into it. The sperm are
unique in that they lack flagella
and move by pseudopodia, like
amoebas.
Figure 1. Cross section of female Nematode.
Procedure:
1. Refer to pages 94-95 in your photo atlas as you work through this exercise.
2. Obtain dissection tools and a preserved Ascaris.
3. Determine its sex. The male is much smaller than the female and has a hooked posterior end.
4. Using a stereoscopic microscope, look at the ends of the worm. A mouth’s present at the
anterior end. Three ”lips” border this opening. A small slit-like anus is located ventrally
near the posterior end of the animal.
5. Pin the anterior and posterior ends of the worm to your dissecting tray. Pin it near the edge
of the pan to allow for viewing in the stereoscopic microscope.
6. Open the animal by making a mid-dorsal incision along the length of the body with a sharp
scalpel or scissor. Be careful not to go too deep. Once the animal is open, pin (in an angle)
the free edges of the body wall to the dissection pan, spreading open the body.
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BIO170 General Biology Freeman/Mac Leod FMCC
7. The most obvious organs you will see in the dissected worm are reproductive organs, which
appear as masses of coiled tubules of varying diameters.
8. Identify the flattened intestine, extending from mouth to anus.
9. Locate two pale lines running laterally along the length of the body in the body wall. The
excretory system consists of two longitudinal tubes lying in these two lateral lines.
10. There are no organs for gas exchange or circulation. How does the worm exchange oxygen
and carbon dioxide with its environment?
11. Do you see a circulatory system? How would nourishment be taken into the body and be
circulated?
12. Do you see signs of segmentation in the body wall or in the digestive, reproductive, or
excretory systems?
13. What do you think supports the body?
14. Draw and label the bold terms above your observations in your notebook.
15. Obtain a prepared slide of a female Ascaris cross section. Observe the slide using a
compound microscope.
16. Note that the body wall is made up of cuticle (non-cellular), epidermis (cellular) and muscle
fibers.
17. Locate the intestine (derived from endoderm) and the pseudocoelom. Note that the
pseudocoelom is lined by muscle distally. The gut does not have associated muscle. How do
you think food is moved along the digestive tract?
18. What do you see inside each uterus?
19. By carefully observing the cross section you should be able to locate the lateral lines
(excretory organs) and the dorsal and ventral nerve cords.
20. Draw and label the bold terms above your observations in your notebook.
21. Complete the summary table that you started last week in your notebook, filling in all
information for characteristics of the Nematodes.
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BIO170 General Biology Freeman/Mac Leod FMCC
B. PHYLUM ARTHROPODA
The phylum Arthropoda (lineage Ecdysozoa) is incredibly diverse. They can be found in almost
every imaginable habitat: air, water (both marine and fresh) and terrestrial. Many species are
directly beneficial to humans, serving a source of food. Others make humans miserable by eating
their homes, infesting their domestic animals, eating their food and biting their bodies. Despite
this unbelievable diversity, the basic body plan of arthropods is fairly constant. Arthropods have
a stiff cuticle made largely of chitin and proteins, forming an exoskeleton that may or may not
be further stiffened with calcium carbonate. The exoskeleton is periodically shed as the animal
grows. They have segmented bodies and show various patterns of segment fusion
(tagmatization) to form tagmata (heads, abdomens, etc.). The phylum takes its name from its
distinctive jointed appendages, which may be modified in a number of ways to form antennae,
mouthparts, and reproductive organs. Arthropods also have a hemocoel, an open body cavity in
which blood flows and bathes the tissues and organs. They generally lack blood vessels. The
dorsal tubular heart is perforated by pores (ostia).
In this exercise you will observe two arthropods: the crayfish (aquatic) and the grasshopper
(terrestrial).
CRAYFISH (Cambarus)
The crayfish, a crustacean, lives in streams, ponds and swamps, usually protected under rocks
and vegetation. It may walk slowly over the substrate or swim rapidly using its tail.
Procedure:
1. Refer to pages 101-102 in your photo atlas and Figures 2 and 3 as you work through this
exercise.
2. Obtain a preserved crayfish and dissection tools.
3. The body is divided into 3 tagmata: head, thorax and abdomen.
4. Crayfish have pronounced cephalization. Locate the eyes, antennae and antennules used
for sensing their environment.
5. Appendages grouped in each region perform specific functions. Locate the maxillipeds,
maxilla and mandibles used for eating. Movement is accomplished using walking legs and
swimmerets. Group these appendages in each of the 3 tagmata.
6. Note the large pair of chelipeds. These are used for feeding and defense.
7. Draw and label the bold terms above your observations in your notebook.
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BIO170 General Biology Freeman/Mac Leod FMCC
8. Male crayfish have a pair of specialized swimmerets called copulatory swimmerets that
females lack. What sex is your crayfish?
9. To expose the feathery gills, use scissors to cut away a portion of the carapace on the left
side of the animal. What is the function of the gills?
Figure 2. External anatomy of the crayfish
Figure 3. Dorsal dissection of a crayfish
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BIO170 General Biology Freeman/Mac Leod FMCC
10. To remove the dorsal portion of the carapace, start on each side of the body at the posterior
edge of the carapace and make two lateral cuts extending along each side of the thorax and
forward over the head, meeting just behind the eyes. This should create a dorsal flap in the
carapace.
11. Carefully insert a needle under this flap and separate the underlying tissues as you lift the
flap.
12. Observe the heart, a small angular structure located just under the carapace near the
posterior portion of the thorax. (If you were not successful in leaving the tissues behind as
you removed the carapace, you may have removed the heart with the carapace). You may be
able to see thin thread-like arteries leading out from the heart. Look for holes in the heart
wall. When blood collects in sinuses around the heart, the heart relaxes, and these holes open
to allow the heart to fill with blood. The holes then close, and the blood is pumped through
the arteries, which distribute it around the body. Blood seeps back to the heart, since no veins
are present. What is the name given to this kind of circulatory system?
13. Locate the cardiac stomach in the head region. It is large sac-like structure. It may be
obscured by the large, white digestive glands that fill the body cavity inside the body wall.
14. Leading posteriorly from the stomach is the intestine. Make longitudinal cuts through the
exoskeleton on either side of the dorsal midline of the abdomen. Lift the exoskeleton and
trace the intestine to the anus. (When shrimp are deveined the intestine is removed).
15. Turn your attention to the anterior end of the specimen again. Pull the stomach posteriorly
(this will tear the esophagus) and look inside the most anterior portion of the head. Two
green glands (do not look green), the animal’s excretory organs, are located in this region.
These are actually long tubular structures that resemble nephridia but are compacted into a
glandular mass. Waste and excess water passes from these glands to the outside of the body
through pores at the base of the antennae on the head.
16. Observe the brain just anterior to the green glands. It lies in the midline with nerves
extending posteriorly, fusing to form a ventral nerve cord.
17. Draw and label the bold terms above your observations in your notebook.
18. Complete the summary table that you started last week in your notebook, filling in all
information for characteristics of the Crayfish.
GRASSHOPPER (Romalea)
The grasshopper, an insect, is an example of a terrestrial arthropod. Insects are the most
successful and abundant of all land animals. They are the principle invertebrates in dry
environments and they can survive extreme temperatures. They are the only invertebrates that
can fly. The effect of grasshoppers on the ecosystem is two-fold. As herbivores they link plants
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BIO170 General Biology Freeman/Mac Leod FMCC
to the rest of the ecosystem in the food web. Grasshopper frass (droppings) contribute to
nutrient turnover by returning nutrients as fertilizer for the plants. They provide food for birds
and other arthropods. On the other hand, some species of grasshopper occur in very large
numbers and cause serious crop damage. As you study the grasshopper, compare the anatomy of
this terrestrial animal with the aquatic crayfish just studied. This comparison should suggest
ways that terrestrial animals have solved the problems of life out of water.
Procedure:
1. Refer to page 103 in your photo atlas and figures 4 and 5 as you work through this exercise.
2. Obtain dissecting tools and a preserved grasshopper.
Figure 4. External anatomy of a female grasshopper
3. Like the crayfish, the body is divided into 3 tagmata: head, thorax and abdomen.
4. Grasshoppers have pronounced cephalization. Locate the compound eyes and antennae
used for sensing their environment.
5. Appendages grouped in each region perform specific functions. Locate the mouthparts used
for eating. Movement is accomplished using legs and wings. Note that there are no
appendages associated with the abdomen. Much of the abdomen is composed of intestine
and reproductive structures.
6. Along the sides of the abdomen you will see some small dots. These dots are spiracles, small
openings into the tracheae. This branch like structure is the respiratory system of the
grasshopper.
7. Draw and label the bold terms above your observations in your notebook.
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BIO170 General Biology Freeman/Mac Leod FMCC
8. To remove the exoskeleton, first take off the wings and, starting at the posterior end, use
scissors to make two lateral cuts toward the head. Remove the dorsal wall of the exoskeleton
and note the segmented pattern of muscles inside the body wall.
Figure 5. Internal Anatomy of a grasshopper
9. A space between the body wall and the digestive tract, the hemocoel (true coelom), in life is
filled with colorless blood. The heart of the grasshopper is an elongated, tubular structure
lying just inside the mid-dorsal body wall. (This probably will not be visible). Like the
crayfish, the grasshopper does not have blood vessels. How do we classify this type of
circulatory system?
10. Follow the digestive tract by starting at the mouth. Along, the lengths of the tract are regions
specialized for specific functions. A narrow esophagus leading from the mouth expands into
a large crop used for food storage. The crop empties into the stomach, where digestion takes
place. Six pairs of finger-like extensions called gastric ceca connect to the digestive tract
where the crop and the stomach meet. This organ secretes digestive enzymes. Food passes
from the stomach into the intestine, then into the rectum and out the anus.
11. The excretory system is made up of numerous tiny tubules, the Malpighian tubules, which
empty their products into the anterior end of the intestine. These tubules remove nitrogenous
wastes and salts from the blood.
12. Push aside the digestive tract and locate the ventral nerve cord lying medially inside the
ventral body wall. Ganglia are expended regions of the ventral cord. Note that each segment
has a ganglion. The branches from the nerve cord pass around the esophagus and meet,
forming a brain in the head.
13. Draw and label the bold terms above your observations in your notebook.
14. Complete the summary table that you started last week in your notebook, filling in all
information for characteristics of the grasshopper.
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BIO170 General Biology Freeman/Mac Leod FMCC
C. PHYLUM ECHINODERMATA
The Echinodermata is one of the three phyla in the group of animals called deuterostomes.
Remember that in this lineage the blastopore develops into the anus. The Echinodermata get
their name from the spines that many species in this group possess. Examples of echinoderms
include the sea star, sea urchin, sea cucumber and sea lily.
In this exercise you will examine and observe the dissection of an echinoderm, the adult sea star
(demonstration only). Even though echinoderms are in the Bilateria lineage, adult forms, like the
Sea stars are radially symmetric. It is their larval form that is bilateral.
Procedure:
1. Refer to page 105 in your photo atlas and Figures 6, 7 and 8 as you work through this
exercise. Your instructor will demonstrate this dissection.
2. Sea stars detect light with five purple eyespots at the end of each arm.
3. The bright orange dot on the aboral surface in the central disk of the body is called the
madreporite. This organ pumps water into the sea star's water vascular system. This
pumping action creates suction at the end of hundreds of tube feet, located in paired rows on
the oral surface.
4. The spines of the sea star are bony plates covered with epidermis. The epidermis also
contains fleshy skin gills for gas exchange.
5. As your instructor removes the body wall from an arm and the central disk, note the massive
digestive glands (also called pyloric caeca) with secrete digestive enzymes into the pyloric
stomach. Beneath the pyloric stomach is the cardiac stomach. This portion of the digestive
tract can be everted into a clam where initial digestion takes place. The cardiac stomach is
then retracted and partially digested material is sucked into the mouth. These animals do not
have a true intestine. Rather, they have a short rectal tube that leads to the anus on the aboral
surface.
6. Looking back at the aboral surface, follow the madreporite to the stone canal that leads to
the ring canal of the water vascular system. Radial canals extend from the ring canal into
each arm. On either side of the radial canal you will see ampullae. Muscles around the
ampullae create water pressure in the tube feet, suction cup like structures that allow the
organism to move.
7. Sea stars reproduce sexually with individuals being either male or female. It is hard to
distinguish the sexes unless they are actively reproducing. You may be able to see the
gonads located on the oral surface of the dissected arm.
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BIO170 General Biology Freeman/Mac Leod FMCC
Figure 6. Detail of Sea Star body wall anatomy
Figure 7. Anatomy of a Sea Star
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BIO170 General Biology Freeman/Mac Leod FMCC
Figure 8. Water Vascular system of the Sea Star
8. Though you do NOT have to draw this in your notebook, you are responsible for all the
bold terms above.
9. Complete the summary table that you started last week in your notebook, filling in all
information for characteristics of the Echinodermata.
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