A queen conch (pronounced "konk") shell Sea snails and slugs move about on one large foot. Sea snails, a family that includes limpets, conches, whelks and periwinkles, all have hard shells, while sea slugs do not. Because sea slugs are not protected by a shell, some species are camouflaged and some are poisonous. Snails and slugs are gastropods, types of mollusc. Other molluscs are bivalves and the cephalopods: squid, cuttlefish and octopuses.
Limpets are kinds of sea snails that have a simple, conical shell. Some limpets, especially those that live in intertidal zones (between the high tide and low tide marks), have a lung, while others have gills. Using their single muscular foot, limpets attach themselves tightly to wet rocks at low tide. They do this to stop themselves drying out or from being pulled away by waves when the tide comes back in. They seal the lower edge of their shells by grinding out the rock, forming a scar in the rock.
At high tide, limpets leave to graze for food. Just before becoming exposed once more at low tide, they return to that same scar.
There are over 62,000 known species of gastropod living in marine, freshwater and land environments—and there may be up to 90,000 more to be discovered.
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