Seashells can often be identified by their shape, size, color and habitat, but since there are at least 100,000 species of mollusks, a printed or online identification guide can help. Seashell identification guides provide photographs for comparison, taxonomic details and clues to help differentiate between similar species.
Seashells are the exoskeletons of organisms that live in habitats such as oceans, lakes, streams and sometimes on land. Some seashells wash up on shore after an animal dies and the soft tissue decomposes or is eaten by scavengers. Other shells are discarded periodically when the animal, such as crabs or lobsters, molts.
Marine mollusks are the most common seashells found on beaches because their shells are very durable. The species includes clams, snails, tusk shells, chitons and nautiluses. Other seashell specimens may include barnacles, sea urchins, brachiopods, which look similar to mollusks, and annelid worms, which are usually permanently attached to another surface. Cephalopods, like octopuses, also produce shells, but most species grow their shell internally.
Some less common shells include sea turtle shells, hard and soft coral exoskeletons and plankton, which may not be visible to the naked eye. Some seashells are fragments of an exoskeleton, such as the “butterfly shells,” that are part of the horseshoe crab exoskeleton.
Land and freshwater shells are not as common as marine varieties. The greatest variety of marine mollusks are found in tropical climates.