Yes. As in most molluscs, the bivalves' (clams, mussels, and oysters) blood circulation is mainly open. The heart has three chambers, two antechambers (atria) and one heart chamber (ventricle).
Bivalves belong to the invertebrate phylum Mollusca, which also includes snails, squids, and octopuses. Some well-known bivalves include clams, scallops, mussels, and oysters. More than 15,000 species of bivalves exist. All bivalves are aquatic, encompassing both marine and fresh-water species.
Clams live underground, using a muscular foot to dig down into sand or mud. They take in water for filter feeding and gas exchange through an extended part of the body called the siphon, or neck. The siphon is also used to disperse eggs or sperm. In some species, such as the geoduck clam, the siphon is extremely long, allowing the clam to remain safe deep underground. The geoduck is the world's largest burrowing clam, and can live up to 145 years.
Mussels are sedentary bivalves. They attach themselves to a firm substrate using secreted threads known as byssal threads, which are produced by the byssal organ of the muscular foot. Mussels frequently occur in large colonies, forming mussel beds. Like other bivalves, they are filter feeders.
Oysters are sessile (nonmotile) bivalves that live attached to substrates such as rocks. Like many other bivalves, they occur in beds and are filter feeders. Oyster shells tend to be rough on the outside but smooth on the inside.
Find Fun Shellfish Facts at Massachusetts Aquaculture Association.