What Type of Animals Should I Expect to See in the Touch Tanks?

7 June 2002

Knobbed Whelk Busycon carica

Mollusks

Most animals with shell “houses” to protect their soft bodies are called mollusks. Oysters, clams, scallops, and whelks are all mollusks. These animals have a mantle of soft tissue inside the shell. The edge of the mantle secretes calcium carbonate that turns to shell when it mixes with sea water.

Whelks are large snails that live in sandy areas. The soft body of the whelk is protected by a heavy shell. The sharp edge of this shell is used by the whelk to pry open clams to eat.

These animals have a head with eyes and two pairs of tentacles that contain organs of feel, taste, and smell. The sharp file-like tongue called a radula is used to cut or tear food. Whelks also have gills that remove oxygen from the surrounding sea water.

Whelks move by means of a thick muscular foot pushed out of the bottom of the open shell. The animal can withdraw the foot and other body parts and close the opening with a trap door called an operculum.

Snails have a single shell and are called univalves. Clams have two shells and are called bivalves. Clams and other bivalves are filter feeding animals that use siphon-like tubes to draw water through an organ that traps tiny plankton that the clam eats. Clams pull themselves through mud and sand by means of a single wedge-shaped foot.

Oysters cement themselves to hard objects located between the high and low tide water lines and are unable to move about.

Scallops are the fastest bivalves. They rapidly open and close their two shells like castanets and pulse through the water to escape enemies.

Common Sea Star Asterias forbesii

Sea Stars

The sea star or starfish is a spiny-skinned animal that has from five to fifty arms or rays. The small spines projecting through their skin cause these animals to feel rough. They can grow new arms if one is injured or lost, though this process may take weeks to complete.

Sea stars use the hundreds of small tube feet on their arms to pull open a clam to eat. These tube feet are operated by a hydraulic system using sea water. The mouth is located on the underside of the animal.

Hermit Crabs

Thinstripe Hermit Crab Clibanarius vittatus

The hermit crab is a crustacean and a close relative of the shrimp, lobster, and blue crab. It has five pairs of legs. The first pair of legs is claws, the second and third pairs are used for walking, and the last two pairs are used to hold the crab securely in its borrowed shell

Hermit crabs live in empty mollusk shells that they find, and as the hermit crab grows, it must find a larger shell. The shell protects the crab’s soft rear body parts

Horseshoe Crabs

Horseshoe Crab Limulus polyphemus

Horseshoe crabs, which are more closely related to spiders and other arachnids than to crustaceans, have lived on the earth for millions of years. Although the horseshoe crab looks menacing, it is harmless. Its long tail is used to turn itself over – not as a weapon.

The horseshoe crab has jointed legs and an outer shell (exoskeleton) of chitin that is shed periodically as its body grows. It uses the front of its round shell to plow through the sand to uncover worms and clams which it feeds upon.

Horseshoe crabs have copper in their blood which gives it a blue color. Their blood is used in testing pharmaceutical products.

Spider Crabs

Portly Spider Crab Libinia emarginata

Spider crabs are found in a variety of habitats such as eel grass beds and open sandy bottoms where they feed on scavenged items. Their shell, which is covered with short curved hair, frequently has algae, bryozoans,

sponges, and barnacles growing over it. The spider crab’s shell may grow to four inches in diameter; its leg span can measure up to one foot.

PLEASE NOTE: The species of animals found in each of the the NC Aquarium touch tanks varies seasonally.