Final answer:
Class Bivalvia in Phylum Mollusca includes bivalved mollusks like clams and oysters. They have bilaterally symmetrical bodies with calcium carbonate shells and lack a radula, instead having specialized gills called ctenidia for filter-feeding.
Step-by-step explanation:
Characteristics of Class Bivalvia in Phylum Mollusca
Members of the class Bivalvia are bilaterally symmetrical with bodies protected by two calcium carbonate shells or valves. These bivalves, including clams, oysters, mussels, and scallops, are primarily found in both marine and freshwater habitats. They first appeared in the Cambrian period and possess several layers in their shells, including an outer organic layer, a prismatic layer, and a smooth nacreous layer, with the oldest part of the shell being called the umbo. Bivalves lack a radula, which is commonly present in other molluscan classes, and instead filter-feed by siphoning water through their gills or ctenidia for food and gas exchange.
Their body plan includes a wedge-shaped foot and a poorly developed head region, and excretion, as well as osmoregulation, are facilitated by a pair of nephridia.Class Bivalvia in Phylum Mollusca includes bivalved mollusks like clams and oysters. They have bilaterally symmetrical bodies with calcium carbonate shells and lack a radula, instead having specialized gills called ctenidia for filter-feeding.