Bivalve mollusks (e.g., clams, oysters, mussels, scallops) have an external covering that is a two-part hinged shell that contains a soft-bodied invertebrate. A roughfile clam from the Flower Garden Bank National Marine Sanctuary—just one of many different bivalve mollusk species.
Early cephalopods are thought to have produced jets by drawing their body into their shells, as Nautilus does today. Nautilus is also capable of creating a jet by undulations of its funnel; this slower flow of water is more suited to the extraction of oxygen from the water.
Examples of gastropods include whelks, conchs, periwinkles, abalone, limpets, and nudibranchs. Gastropoda Characteristics. Many gastropods such as snails and limpets have one shell. Sea slugs, like nudibranchs and sea hares, do not have a shell, although they may have an internal shell made of protein.
Seashells are an important part of biological and geological beach processes as well as an important part of human culture. The organisms that produce the shells provide huge quantities of food for animals including people forming the basis of a multi-billion dollar portion of the global commercial fishing industry.
Chitons / ˈ k aɪ t ən z / are marine molluscs of varying size in the class Polyplacophora, formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as sea cradles or "coat-of-mail shells", or more formally as loricates, polyplacophorans, and occasionally as polyplacophores.