Different Types of Seashells
Seashells are the exoskeletons of marine creatures, usually mollusks. Animals with exoskeletons have skeletons on the outside of their bodies instead of on the inside. (Insects, for example, have exoskeletons.) Mollusks, meanwhile, are invertebrates: they have no spine. Types of mollusks include gastropods, bivalves, cephalopods, scaphopods, chitons and monoplacophores. Mollusks are divided according to the kind of shell they have, among other things.
Other People Are Reading
-
Gastropods
-
Gastropods are the snails and slugs of the world---not only those in the sea---as well as the whelks. "Gastropod" comes from the Greek words for "stomach" and "foot." Since gastropods include both terrestrial and water creatures, their habitats are many and varied. We see gastropods in our yards and gardens, in the woods and mountains, and in lakes, rivers and oceans. Ocean gastropods give us abalone shells, conches, whelks and limpets. Many gastropods have shells that coil out to the side. Gastropods are sometimes called univalves.
Bivalves
-
The shells of bivalves are very recognizable because they are hinged. Botticelli's famous painting, "The Birth of Venus," features the goddess rising out of the sea atop a bivalve half-shell. The two halves of a bivalve look like two different shells, but bivalves are actually two parts that are hinged together with a ligament to form one shell. Each half of the shell is called a valve. Bivalves include scallops, clams, oysters and mussels, all of which are edible. Bivalves are only found in water, usually in saltwater.
-
Cephalopods
-
"Cephalopod" is from the Greek and means "head-foot." The head part comes from the fact that cephalopods have prominent heads. This class of animal includes the octopus, scuttlefish and squid. In some cephalopods, there is no shell, but another subclass of cephalopod does possess a shell. This class includes the nautilus, which is the only cephalopod with a real external shell. Some cephalopods have internal shells. Ammonites are an extinct cephalopod that had shells, and their shells can be found as fossils.
Scaphopods
-
Scaphopods are shells that look like tusks or teeth, shaped like arced cones. They are light-colored and have openings at both ends.They are usually quite small, so they can be hard to see on a beach. Some, though, can be as long as about 6 inches. They are the most recent mollusks to evolve, developing during the Ordovician period, about 450 million years ago. Native Americans of the Pacific Northwest collected scaphopods as money. The word "scaphopod" comes from the Greek for "boat" and "foot."
Chitons
-
Chitons are sea animals that like to live near rocky places, often near the shore in intertidal zones, which means that, at low tide, they are in the air and sun. Species range in size from less than 1/2 inch to almost 12 inches. Chiton shells have 8 plates (valves) that overlap. When the shells wash up on shore, they have usually come apart.
Monoplacophores
-
These sea-floor creatures were thought to be extinct, with fossil records showing them living 350 million years ago. In 1952, though, live monoplacophores were found off Costa Rica. Monoplacophores are very small and tend to live in deeper waters. The shell of this animal cups over its wearer, which uses a large foot to move.
Other "Shells"
-
Besides mollusk shells, there are many other finds that people combing the beach consider seashells. Some of these are the exoskeletons of other creatures, for instance, crustaceans, such as barnacles and lobsters. Other non-mollusk finds include teeth from sharks and the famous sand dollar, which is a relative of the sea urchin.
-
