Supergroup Opisthokonta – Basal Animals and Deuterostomes – 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: Examine preserved sponges

Examine the preserved sponge specimens. The sponges that look like a kitchen sponge belong to Class Demospongiae Their spicules are composed of a protein, spongin. The Demosponges on display have been treated to remove the cells. The remains are the flexible network of spicules. Demosponge remains used to be commonly used as a household cleaning item; today, most household sponges are synthetic.

There are also representatives of Class Hexactinellida on display. These are commonly called the glass sponges, because their spicules are made of silica. Examine the long, hairlike spicules at the base of the glass sponge. What function do you think these serve?

Glass sponges often live deep in the ocean, from 180 to 2000 meters. They are also relatively abundant in the Southern Ocean around Antarctica. There are about 500 described species.

Why do you think the body wall of many sponges is folded?

Exercise 1.2: Examine prepared slide of Grantia

Sketch and label a portion of your field of view. Include the following structures, if observed: spongocoel (large hollow cavity inside sponge), radial canals (canals in the body wall continuous with the spongocoel and lined with choanocytes), and ostia(singular: ostium, small pores in the outer wall of the sponge to allow water to enter).

Exercise 1.3: Examine prepared slide of spicules

Grantia is a calcareous sponge, meaning it has spicules made of calcium carbonate. This sponge belongs to Class Calcarea. Examine the prepared slide of its spicules and sketch a few of them.

Exercise 1.4: Examine live Spongilla

Spongilla is a freshwater sponge of Class Demospongiae. It has multiple oscula. Observe under the stereo microscope. Do you see spicules projecting from the mesohyl at the edges of the sponge?

It can reproduce sexually, giving rise to free-swimming larvae, or it can reproduce asexually by means of gemmules. These consist of amoebocytes surrounded by spicule. They are produced in response to cold and can lie dormant

Do you observe any gemmules? How would these be advantageous to a freshwater sponge that lives in temperate climates?

What color is Spongilla? The color is not produced by the sponge, but by symbiotic organisms. Based on the color, what kind of organism do you think forms symbioses with Spongilla?

Sketch the Spongilla, labeling the spicules, oscula and gemmules, if observed.

Exercise 1.5: Extract spicules from Spongilla

Each group should complete this preparation.

  1. Remove a small portion of the sponge and place in an Eppendorf microtube.
  2. Add enough bleach to cover the sponge.
  3. Incubate at room temperature for 30-60 minutes.
  4. Mix gently with a pipet and remove a drop or two. Place on slide, add a coverslip, and observe under the compound microscope.

Do you see spicules? What shape are they? Draw a few.


Exercise 2.1: Examine preserved Hydrozoans

Observe the preserved hydrozoans on display. Many hydrozoans are colonial. The Portuguese man o’ war (Physalia), for instance, is a colony composed of both polyps and medusae.

Exercise 2.2: Examine prepared slide of Obelia, a hydrozoan

Obelia is a hydrozoan that alternates between a colonial polyp form and a free-swimming medusa form. Examine the Obeliacolony. What difference(s) do you observe between a feeding polyp and a reproductive polyp?

Exercise 2.3: Examine and feed Hydra, a hydrozoan

Obtain a living Hydra specimen and observe under the microscope. How many tentacles do you see surrounding the mouth?

What kind of body symmetry does Hydra display? Is this typical of cnidarians?

Do you observe budding in your Hydra specimen? If so, please alert your instructor.

Add a drop of water containing Daphnia (a small crustacean) to your depression slide and add a cover slip. Observe under the 10x objective of your compound microscope. Do you observe Hydra feeding on Daphnia? You may have to watch for several minutes. 

Exercise 2.4: Examine preserved scyphozoans

Observe the preserved moon jelly (Aurelia). You may handle it with gloves on. Sketch and label the tentacles (there are many small tentacles around the margin of the animal), gonads (the four C-shaped structures near the center), oral arms (four long structures projecting from ventral surface), and mouth (in the center of the ventral surface of the animal).

Exercise 2.5: Examine preserved anthozoans

Examine the preserved specimens of sea fans (also called gorgonians), corals, and sea anemone. Sea fans and coral are colonial anthozoans. Do you see the small depressions that would have housed each individual polyp?


Exercise 3.1: Examine preserved lancelet (Amphioxus)

Lancelets are one of the few invertebrate chordates. They have the four distinctive characters of chordates – pharyngeal gill slides, dorsal, hollow nerve cord, notochord, and post-anal tail.

Exercise 3.2: Examine prepared slide of a lancelet 

Sketch the lancelet and try to identify the four characters of chordates.

Exercise 3.3: Examine a preserved tunicate 

Tunicates are also invertebrate chordates. Although the adult form of the animal does not look very similar to vertebrates, tunicate larvae do have chordate characteristics. These are mostly lost during metamorphosis. 

Exercise 3.4: Examine preserved and prepared slide of lamprey

Note the pharyngeal slits. Also examine the mouth. Lampreys obtain nutrients by attaching to the side of a fish, scraping a hole in its side, and feeding on its blood.

Exercise 3.5: Examine preserved specimens of chordates

These are the more familiar representatives of Phylum Chordata. Which features of chordates are retained into adulthood?

Exercise 3.6: Dissect a chordate

In groups of 4-5, dissect a rat or other chordate.


Exercise 4: Examine preserved hemichordate

Examine the preserved acorn worm specimen. Although this worm looks similar to other worm groups, it is unique among worms because of its dorsal, hollow nerve cord and pharyngeal gill slits, two characters that chordates also possess. Based on these morphological traits and molecular sequencing, we can hypothesize that hemichordates are closely related to chordates. 


Exercise 5.1: Examine preserved starfish (Class Asteroidea)

Examine the preserved sea stars on display. You may handle the preserved specimen with gloves on. Find the madreporite on the dorsal surface. The anus is also on the dorsal surface. On the ventral surface, observe the tube feet, mouth, and radial canal.

Exercise 5.2: Examine preserved sea cucumber (Class Holothuroidea)

Sea cucumbers appear to be soft-bodied animals; however, they do have an endoskeleton. In most species, it is greatly reduced. The mouth has tentacles surround it; these are modified tube feet. When threatened, some sea cucumbers can eject some of their internal organs. They can then regenerate these over a period of several weeks. 

Does the sea cucumber have pentaradial symmetry?

Exercise 5.3: Examine specimens of sea urchins (Class Echinoidea)

Examine the sea urchin test. Find the hole at the top of the test. This is the anus of animal. The five plates surrounding it are genital plates. One is larger than the others; this one has been modified to serve as the madreporite.

Looking from the top down, can you see the pentaradial symmetry?

Exercise 5.4: Examine specimens of sand dollars (Class Echinoidea)

Now observe the sand dollars. Sand dollars are modified sea urchins. Observe the preserved sand dollar to see the skin with its small spines.

Look at the sand dollar test. Unlike most sea urchins, the anus is on the underside, along with the mouth.

Preparation for lab next week: the protostomes

Exercise 6: rehydrate tardigrades

Rehydrate your tardigrades by adding dH2O. Observe them under the microscope. Do you observe any tuns? By the end of lab, have any tardigrades exhibited movement or recovery from the tun stage? If not, place them back in the hood to observe next week.

Exercise 7: Observe cut planarians

Observe your planarians. Have they regenerated? Completely or partially?

Feed the planarians with whatever food your instructor provides. Observe them feeding with the muscular pharanyx.

Do you predict that the planarians will completely regenerate by lab next week?