Pelecypod is a term that describes a type of mollusk with a vertically hinged shell, also known as bivalve. Bivalves are found in freshwater and marine environments and are an essential part of the aquatic food chain. While pelecypod is the most commonly used term for this type of mollusk, there are several synonyms for it. These include bivalve, shellfish, clam, oyster, and mussel. Bivalves are valued for their taste and nutritional content and are farmed for commercial purposes. They are also important for maintaining the health of the ecosystem as they filter water and provide habitats for other marine organisms.