bivalvian

Bivalvian refers to any member of the class Bivalvia, which is a major group within the phylum Mollusca. Bivalves are characterized by their two-part shell, known as valves, which are hinged together. These shells are typically composed of calcium carbonate and are secreted by the mantle, a specialized tissue that lines the inside of the shell. Bivalves lack a distinct head and possess a filter-feeding apparatus consisting of gills that also function in respiration. They have a simple nervous system and a circulatory system with a heart.

The class Bivalvia encompasses a vast diversity of species found in marine, brackish, and freshwater environments worldwide. Common examples include oysters, mussels, clams, scallops, and cockles. Many bivalves are sessile, attaching themselves to substrates, while others can burrow into sediment or swim. Their diet consists primarily of plankton and other small organic particles filtered from the water. Reproduction in bivalves is typically sexual, with external fertilization being common, although some species exhibit internal fertilization or brood their young. Bivalves play crucial roles in aquatic ecosystems, acting as filter feeders that improve water quality and serving as a food source for various predators. They also have significant economic importance as a source of food and pearls.