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Background:
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Living organisms differ greatly in size, shape, color, means of protection from predators, means of moving from one place to another, foods eaten, method of feeding on those foods, growth processes, methods of excretion, lifespan, and many other characteristics. Some of these characteristics will be studied by observing and handling five living organisms.
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Explanation:
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A horseshoe crab has a brown, horseshoe-shaped protective shield or shell which is somewhat like a turtle shell. The shell may be several inches to more than two feet from front to back. Unlike other crabs, the horseshoe crab has a long spine-like tail or telson which, the horseshoe crab has a long spine-like tail owhich may be nearly as long as the shell itself. The segmented body of the horseshoe crab lies underneath the shell. It includes a combined head and thorax with a mouth, a pair of sharp pincers used for biting prey, a pair of jointed legs that may assist walking or serve as sense organs, and four pairs of jointed walking legs with pincers on the end. The mouth lies in the center of the area surrounded by the legs. The part toward the tail forms. Horseshoe crabs feed on small sea animals such as annelids and the abdomen which is comprised of a series of flap-like gills. Horseshoe crabs plow through the mud by arching the body and pushing with the telson and the last legs. Horseshoe crabs feed on small sea animals such as worms and soft-shelled clams.
The body of a sea urchin is shaped like a ball that is somewhat flattened on the bottom. The body has a pink skin which is covered with sharp, movable, white spines for protection. Like a starfish, a sea urchin has a five-part body plan whin which is seen on the underside in the five rows of tube feet that extend through its skeleton. These tube feet allow the sea urchin to creep i when the tube feet become stiff enough to support the body and pull the body forward by means of a sucker-like acti to creep in all horizontal directions when they become stiff enough to support the body and pull the body forward by means of a sucker-like action onto a hard surface. The sea urchin has a large hole on the underside which is covered with skin. The mouth, jaws, and teeth are in the center of that hole. Most sea urchins are vegetarians and feed on algae, but the jaws and teeth can also grind small sea animals.
A snail has a very soft body, but differs from a slug in that it is covered with a protective spiral shell. The shell is compact, strong, and portable, providing both protection and mobility. The shell grows as the soft body grows and covers and protects the soft body. The soft body is attached to the shell by long, powerful mues that are connscles that are connected to the central pillar of the shell. The soft body has a head/foot portion which faces forward and can be pushed out of or withdrawn into the shell. The head has four tentacles. The tips of the outer longer pair of tentacles contain eyes. The foot is used for movement. Snails leave slime behind them to help them move and keep them moist. Larger teeth on a tongue-like, ribbon-like device called a radula cut and tear leaves or other food materials, and smaller teeth pull pieces of algae, clams, or oysters into the mouth.
A spider crab has a triangular or oval body and long, slender legs. It is distinguished from a lobster by its short tail which folds under the body. Even for the lobster, what we call the tail is really part of the abdomen. The spider crab has a heavy shield covering its head and thorax. The spider crab often covers its shell with growing seaweed to provide an effective disguise. The spider crab has many appendages. The spider crab is a scavenger, and the front pair are modified into pincers used for seizing prey. Others are sensory antennae, mouth parts, or legs specialized for feeding, walking, and swimming. Flattened legs are used like flippers for swimming. Legs may be regenerated if left with a predator during an escape. The spider crab walks or crawls with a peculiar side gait.
Starfish range from one-half inch to three feet across. It has a hard outer skeleton of spines embedded in a leathery skin. This protective skeleton covers a central disk and five or more tapering arms or rays arranged like the points of a star and responsible for the star-like shape. The mouth of the starfish is situated. The mouth of the starfish is situated in the center of the underside. Mollusks, barnacles, and worms are the common diet. The starfish eats a clam, for example, by projecting its stomach out through its own mouth and thr, for example, by projecting its stomach out through its mouth and thrrough the crack in a clam shell, digesting the soft tissue of the clam, and withdrawing the stomach back through the mouth of the starfish. There are many pairs of tube feet on the underside of each arm. These tube feet allow the starfish to move when the tube feet become rigid enough to support the body and pull the body forward by means of a sucker-like action onto a hard surface. A starfish can crawl over any surface and squeeze through very narrow crevices.
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Procedure:
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Divide the class into groups of five students each. Allow each group to work with a tray containing one organism, and then switch trays between groups at appropriate time intervals.
Give each student an opportunity to handle each of the five living marine organisms (horseshoe crab, sea urchin, snail, spider crab, and starfish). The task of each student group is to determine for each organism (1) its method of protection;
(2) its method of movement; and (3) its method of feeding. Students should record observations and ideas about each of
these methods.
After an appropriate period for observation, the teacher discusses the survival behavior of each organism, taking suggestions from the class.
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