Supergroup Opisthokonta – Protostomes – Lab Exercises

Please choose one live specimen or prepared slide to image. Take a picture under the microscope and submit via Canvas. Make sure that your picture is appropriately centered, cropped, and focused. Add a scale bar.


Exercise 1.1: Observe the planarians cut last week for regeneration

Find your planarians and evaluate how well they regenerated. 

Are they fully regenerated? (i.e., have all pieces developed into a full-size, fully pigmented adult worm?)

If not, describe the worms and the regeneration that has taken place so far. 

Exercise 1.2: Examine Fasciola hepatica

Fasciola hepatica is also known as the common liver fluke. It has a complex life cycle, with snails serving as the intermediate host. Large mammals such as sheep, cows, or (sometimes) humans act as the definitive host (the host in which sexual reproduction occurs). Juvenile flukes are ingested with contaminated water or water plants. They are able to penetrate the intestinal wall and migrate into other tissues, especially the bile ducts and the liver. The CDC estimates that more than 2 million humans worldwide are infected. It is rare in the United States.

Sketch the preserved specimen and identify the oral sucker. This is used to attach to the host.

Exercise 1.3: Examine prepared slide of Clonorchis sinensis

Clonorchis sinensis is another fluke that inhabits the liver and bile ducts. Unlike F. hepatica, this worm is an extremely common parasite of humans. About 30 million humans are estimated to host Chinese liver fluke, mostly in east and southeast Asia. Clonorchis sinensis has two intermediate hosts, snails and fish. The definitive host is a mammal, such as a dog, cat, buffalo, or human. Chinese liver flukes can live for 30 years in humans. It can cause carcinoma of the liver or bile duct.

Examine the liver fluke. Identify the oral suckercecauterus, and testes.

Exercise 1.4: Examine preserved tapeworms

Tapeworms infect the digestive systems of vertebrates. Some scientists have suggested that most, if not all, vertebrate species are parasitized by tapeworms. Tapeworm infections are often asymptomatic. They generally pass through one or more intermediate hosts before reaching the definitive host. Once they do, they use their hooks and suckers to attach to the intestinal wall. They absorb nutrients through the body wall of each segment, or proglottid. Tapeworms can get extremely long, up to ~10 meters in humans, although much longer tapeworms have been reported.

Examine the tapeworms. Each section is a proglottid. Proglottids are produced at the neck of the tapeworm, and continue to be produced throughout life. The widest proglottids are the most posterior. By the time they reach the end of the worm, they contain eggs. Mature proglottids break off the end of the worm and are passed in feces.

Count the number of proglottids in the tapeworm specimen (or count proglottids in a set length and estimate the total number).

Identify the anterior and posterior end of the worm using proglottid thickness.

Exercise 1.5: Examine prepared slide of tapeworm scolex

The scolex is the head region of the tapeworm and is used to attach to the host. Sketch the scolex. Label the hooks and suckers.


Exercise 2: Examine live rotifers

Examine the rotifers. There should be two species. Philodina is a bdelloid rotifer. It has a more pronounced corona than Monostyla, which is a monogonont rotifer. It can switch between sexual and parthenogenetic reproduction.

Draw one of each rotifer species you observe.


Exercise 3.1: Observe preserved chitons

Chitons are members of Class Polyplacophora. They have eight dorsal plates that form a shell. They move by means of their muscular foot.

Sketch a chiton, and label the plates and foot.

Exercise 3.2: Examine shells of gastropods, bivalves, and a cephalopod

A common feature of molluscs is one that makes their remains prized as decorative objects – their shells. Examine the shells on display. Choose six of the shells. For each, place into its correct Class, and list at least one feature of the shell that you predict has evolved as a defense against predators.

ShellClassAnti-predator defense feature

Exercise 3.3: Determine the chirality of gastropod shells

Examine the gastropod shells and record the chirality. Dextral shells coil to the right, while sinistral shells coil to the left. What is the chirality of the shells on display?


Exercise 4.1: Examine preserved Nereis (polychaete)

Nereis is a marine annelid. Sketch the worm, labeling the parapodia (fleshy protrusions) and setae (bristles). These worms tend to burrow in the marine seafloor during the day, leaving their burrows at night to prey on other animals or to graze on algae.

Exercise 4.2: Examine preserved lugworm (polychaete)

Examine the preserved lugworm. Although it may look like an earthworm, it is a marine species that lives in the littoral zone, burrowing in the sand. It seldom leaves its burrow. It eats sand, extracts the nutrients, and then excretes it. Sand castings of lugworms are common on beaches where they live. Find the parapodia.

How does the lugworm differ from Nereis in terms of the number and size of parapodia?

What is your hypothesis regarding why Nereis and the lugworm differ morphologically?

Exercise 4.3: Examine preserved Aphrodita (polychaete)

Aphrodita is a polychaete worm that is named for the appearance of its ventral aspect. It has many parapodia with dense growths of setae, which can give it a furry appearance. This is probably the origin of its other name, the sea mouse. These animals are predators, and feed on other worms and small crustaceans. 

Exercise 4.4: Examine preserved Clitellates

The clitellates include the earthworms and leeches. Examine both under the stereo microscope. Make sure you look at both the ventral and dorsal sides. Do you observe setae (bristles) on either/both?


Exercise 5: Observe rehydrated tardigrades

Locate your tardigrade sample. Observe under the stereo microscope. Have your tardigrades recovered?


Exercise 6.1: Observe live ‘vinegar eels’

Make a wet mount of the vinegar eel culture and observe with the compound microscope. This species, Turbatrix aceti, is a free-living worm that feeds on the bacteria (Acetobacter aceti) that produce acetic acid as a byproduct of ethanol metabolism. They are extremely common in unfiltered vinegar products, including kombucha. They are harmless to humans.

Sketch a vinegar eel. Label the anterior and posterior ends. Can you see the pharynx and intestine?

Exercise 6.2: Examine preserved Ascaris lumbricoides

Ascaris lumbricoides is the most common parasitic worm found in humans. An estimated 1 billion or more people are infected with this worm. The infection is usually asymptomatic, except in people with a heavy worm load. Children are especially vulnerable, and their growth can be restricted by the worms as they are competing with them for nutrition. Ascaris infection is worldwide, including an estimated 4 million cases in the United States. It is most common in areas with poor sanitation. Females are 20-35 cm (~8-14 inches) in length, while males tend to be smaller at 15-30 cm.

Exercise 6.3: Examine prepared slide of Trichinella infection

Trichinella is a nematode that can cause trichinosis in humans, most commonly from eating undercooked pork or game meats that contain Trichinella cysts. Once eaten, the cysts release the larval worms, which quickly mature in the intestinal tract. Within five days, they produce larvae, which penetrate the intestinal wall and migrate to muscle tissue. Here, they form cysts and stay dormant for the life of the host. Although the infection is often asymptomatic or very mild, severe symptoms can be present if the worm burden is heavy. Muscle pain, swelling, and weakness are all possible symptoms. Motor defects and stroke are rare, but can be present if the larvae enter the central nervous system. Trichinosis used to be very common, but now infects only about 11 million humans worldwide. Only a handful of these cases are in the United States.

Sketch the muscle tissue with the encysted Trichinella worm.


Exercise 7.1: Examine trilobites

There are four specimens to examine. Count the number of segments in each specimen.

TrilobiteNumber of segments

Are the segments highly specialized or are they similar in size and shape?

Do you think these trilobites are the same species or different species? Why, and which species concept are you using to make this determination?

Observe the eye of the trilobite under the dissection microscope. Is this a simple or compound eye? How do you know?

Exercise 7.2: Examine horseshoe crabs (chelicerate)

Observe the preserved horseshoe crabs. Horseshoe crabs are divided into two tagmata, the cephalothorax and the abdomen. The long tail spine, or telson, is used for digging, locomotion, and to right the horseshoe crab in case it gets flipped over.

On the dorsal side of the carapace, locate the two compound eyes. The horseshoe crab also has eight simple eyes, or ocelli. The horseshoe crab is often referred to as a “living fossil”, and it is the only chelicerate with compound eyes.

Examine the ventral side of the horseshoe crab. How many segments are there? Identify the five pairs of walking legs. The first pair are the pedipalps. In females, the pedipalps look similar to the other walking legs, while in mature males, the pedipalps are modified to grasp the female during mating. Is this horseshoe crab a male or a female?

Find the chelicerae. These are pincer-like appendages anterior to the mouth. Chelicerae are common to all chelicerates, but have been modified in different groups. In the horseshoe crab, the chelicerae are used to pick up food. The chelicerae pass food back to the gnathobases, tooth-like structures at the base of the walking legs. These break up food and deliver it to the mouth.

Exercise 7.3: Examine arachnids (chelicerates)

Obtain a preserved spider and observe it under the stereo microscope. Although it may look quite different from the horseshoe crab, they are in the same Class. What similarities do you observe?

How many ocelli do you see (most spiders have 6-8)?

Find the chelicerae. In spiders, these have been modified into retractable fang-like structures capable of delivering venom. Thepedipalps in spiders are near the chelicerae, and are used for grasping prey in female spiders (in males, they transfer sperm to the female’s genital opening).

Try to locate the spinnerets on the posterior end of the abdomen. 

Observe the preserved scorpions. Like the horseshoe crab and spiders, scorpions are chelicerates. Find the chelicerae. They will be anterior to the large, pincer-like pedipalps

Exercise 7.4: Observe live millipedes (myriapods)

Observe the live millipedes. You may hold and handle them gently. They are harmless and cannot bite, sting, or pinch. Please wear gloves, as some people are sensitive to their secretions and may develop a rash.

Exercise 7.5: Examine preserved myriapods

Count (or make a good estimate of) the number of segments of one of the myriapods.

Are the segments highly specialized or are they similar in size/shape?

Compare the millipedes to the preserved centipedes. What differences do you observe?

How might these adaptations suit these organisms for their way of life?

Exercise 7.6: Observe live cockroaches (insects)

Observe the live Madagascar hissing cockroaches. You may hold and handle them gently; they are harmless (though they may hiss – please try not to drop them). Examine the compound eyes and antennae. Insects have sophisticated nervous systems that allow them to sense and respond to stimuli. To what kinds of stimuli do you think the antennae respond?

Exercise 7.7: Examine preserved giant beetles (insects)

Observe the large beetles. Please do not touch as these are expensive and fragile.

Both of these are male beetles. The females have smaller or absent horns or pincers. These beetles display sexual selection. Looking at these male beetles, do you think they exhibit (1) intrasexual selection, or (2) intersexual selection? Why?

Exercise 7.8: Examine preserved insects

Examine the preserved insects. Note the diversity of form. Insects have undergone an astonishing adaptive radiation.

Exercise 7.9: Dissect an insect

Exercise 7.10: Examine preserved crustaceans

There are several crustaceans available to observe, including a crab, crayfish, barnacle, decapod, and mantis shrimp. What features do all (or most) of these crustaceans share? 

If you were to make a hypothesis about the relationships of these organisms, which of them would you select as your outgroup? Why? 

Exercise 7.11: Observe live crustaceans (Daphnia)

If available, make a wet mount of Daphnia. Find the compound eyeantennaethoracic appendages, and eggs (if any).