Exercise one to three: Asteroidea
Asteroids are the sea stars, which are the best known echinoderms.
Sea stars usually have five arms, but sometimes more, radiating from a central disk. The ossicles of the body wall are rodlike and articulate via fibrous junctions to form a flexible grid. Respiration is with the tube feet and papulae. Each arm has an eyespot at its tip. A pair of large pyloric ceca and a pair of gonads are present in each arm. Gastric hemal tufts are present.
About 1500 Recent species are known.
Exercise one: Try to film feeding in one of the species available of sea stars. Use chocolate stars (large) or the Asterina (small) species.
(Do not use the blue linckia or sand sifting star for these exercises.
The first is a vegetarian and the latter will not feed unless buried. They are in the lab simply for you to observe.)
Obtain a specimen of one of the species, place in a small dish and add a few
(one maybe two) fish flakes to the dish near the animals for the small species and one small fish for the larger species. You may have to place the larger species on the fish to encourage feeding. Wait till the animals start to feed and then start your observations.
Once they start actively feeding, turn the animal upside down and see if you can see exactly how the animal feeds. The larger species may invert their stomach while feeding.. If the large species is uncooperative, try the smaller species that will almost always feed upside down on fish food. Does the animal’s body move in any way to accommodate feeding? Are the arms involved? Can you see food moving into the mouth?
Exercise two: External Anatomy
Right the animal.
The body is divided into a central disk from which radiate five arms . The principal body axis, and the axis of symmetry, is the short oralaboral axis , which passes vertically through the center of the disk. The animal's pale lower side is the oral surface and structures on this side are

said to be oral . The dark upper side is the aboral surface and structures on this side are aboral . Structures remote from the axis are said to be peripheral whereas those near the axis are central . In radially symmetrical animals anterior-posterior, dorsal-ventral, right-left are irrelevant and have no meaning.
Aboral Surface
Find the calcareous, usually oblong madreporite on the aboral surface of the disk Examine it with the high power of the dissecting microscope and note its grooved surface. Numerous microscopic pores in the bottoms of the grooves open into canals (stone canal and axial canal) of the internal water vascular system .
Orient the star with the aboral side up and with the madreporite close to you. The arm on the left of the madreporite is arm I, arm II is to the right of the madreporite, and the remaining arms are numbered sequentially moving counterclockwise around the star .
Aboral view of Asterias .

The surface is covered by a monociliated epidermis. Can you see evidence of such under the stereoscope?
On the aboral surface notice the numerous small fixed spines , so-called because they are fixed in position and cannot move. These spines are extensions of the calcareous endoskeleton in the body wall. Gently push one of the spines with the tip of a needle to see if it moves. Look closely at the spines with the highest magnification of the dissecting microscope and confirm that they are indeed internal and are covered by a thin layer of living tissue, the epidermis.
See if you can see soft, thin-walled, translucent, fingerlike papulae between the spines as well . Papulae are thin-walled diverticula of the coelom through the body wall and are its respiratory organs. The ciliated peritoneum generates a bidirectional flow of fluid into and out of the papulae. The papulae are muscular and can be retracted into the surface of the body wall. They may be retracted and inconspicuous in somespecimens.
Touch a papula with the microneedle and observe its response.
The anus is located near the center of the aboral surface but is almost impossible to demonstrate externally. It is surrounded by a palisade of tiny ossicles, much smaller than the spines that stud the surface of the disk and is in an area free of papulae.
Exercise two a: Photograph the aboral surface or in large specimen the area aroung madreporite. Label the madreportie and spines.
Oral Surface
Turn the animal over and study the oral surface. Find the large mouth in the center of the disk, surrounded by the thin peristomial membrane . The yellowish-orange curtain-like folds of the cardiac stomach may be visible inside the mouth.
Five deep ambulacral grooves radiate outward from the mouth, one along the midline of the oral surface of each arm . Each groove lies on an

ambulacral axis. The numerous soft, tubular structures projecting into the groove from either side are the tube feet , or podia. Two rows of tube feet are present on each side of the groove. The tube feet of Asterias bear suckers at their distal ends. Note the rows of long, flattened movable spines on each side of the ambulacral groove. The word ambulacrum is
Latin for "covered way," an apt name as these spines are used to cover the groove to protect the tube feet.
Look at the tip of one of the arms . As is usual in radially symmetrical animals, the sensory structures are arrayed around the periphery, which in sea stars is the tips of the arms. Several long, narrow sensory tube feet extend from the tip of each arm. These are easily seen in living specimens but contract and become inconspicuous in preserved material. They have chemo- and mechanoreceptors. At the tip of the arm is a small circle of short, blunt movable spines . These spines surround a small, pale red or yellow eyespot . The eyespot is on the oral surface of the arm, almost at the tip.
Exercise three: a. Take a photograph of one of the arms at high power and label what your can. Turn the animal over and watch it move, which it will want to do and quickly away from you. b. Describe the movement in your journal.