Most molluscs have a hinged two-part shell and include clams, mussels, oysters and scallops, as well as various types of octopus, snail and squid. Many species of molluscs are eaten worldwide, either cooked or raw. Some mollusc species are commercially exploited and shipped as part of the international trade in shellfish; other species are harvested, sold and consumed locally. Some species are collected and eaten locally but are rarely bought and sold.