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members of the class bivalvia

All 15,000 known species of bivalves are aquatic in nature, with close to 80% being marine (saltwater environments). Updates? Bivalves usually live on or in sandy or muddy bottoms. It is 15 to 20 cm in length, has a white, oblong shell, and may weigh as much as 3.6 kg (8 pounds). Test. Marine members of the Bivalvia class are molluscs that have laterally flattened bodies enclosed by a shell formed of two hinged parts. Abstract. Author of. Similar to the gastropods, there are a few species of bivalves that have completely lost their shells through evolution. A block of…. Scallops, Clams, oysters, mussels. Some freshwater species, when exposed to the air, can gape the shell slightly and gas exchange can take place. By limiting shell thickness (which reduces weight), smoothing the shell contours (which reduces drag), and assuming an aerofoil-like leading edge, such scallops can awkwardly swim several metres at a time. Common clams not ordinarily eaten include long siphon clams (Sanguinolariidae), wedge clams (Mesodesmatidae), basket clams (Corbulidae), slender clams (Pandoridae), perforated clams (Thraciidae), and boring clams (see piddock). Such an animal may have a life span of about 40 years. The shell morphology and hinge structure are used in classification. M. mercenaria is about 7.5 to 12.5 cm (3 to 5 inches) long. Terms in this set (11) Key Characteristics. From the simple burrowing, equivalve ancestor, the various bivalve groups have repeatedly evolved an elongated, triangular or circular shell; thus, similar body adaptations have been responses to similar modes of life. One species of abra clam (Abra profundorum), however, has been taken in the Pacific Ocean at a depth of more than 4,800 metres (16,000 feet). Learn. Omissions? Label The Diagram (Fig. Most Sphaerium species are large, about 8 to 20 mm; Pisidium species are the smallest, most ranging in shell length from about 2 to 6 mm; and most Musculium species are intermediate in size, about 8 to 10 mm in shell length, and the shells are thin and fragile. The extinct genus Myalina is important for stratigraphic correlations. M. campechiensis, the southern quahog, is about 7.5 to 15 cm long and has a heavy, white, plump shell. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. All of the following are either structures or characteristics of members of the Class Bivalvia of the Phylum Mollusca except A. The soft-shell clam (Mya arenaria), also known as the longneck clam, or steamer, is a common ingredient of soups and chowders. Notice the rows of blue eyes along the edge of the mantle. These are the scientists who first described the taxon and so should be retained where they are. Anatomy. As the name implies, bivalves have two half-shells called valves that are connected by a dorsal hinge region. Of these, 21 have…, A clamshell is an example of a simple system in which a rigid skeleton is worked by muscles. There are no terrestrial bivalves, although some high-intertidal and freshwater species can withstand drought conditions. Such a shell form and habit evolved first within sediments (endobyssate), where the byssus serves for anchorage and protection when formed into an enclosing nest. Life cycle: Embryos develop into free-swimming trocophore larvae, succeeded by the bivalve veliger, resembling a miniature clam (Ref. D. Turbellarian flatworms have a distict head. The shell is dirty white, oval, and 7.5 to 15 cm long. You may have seen or even eaten an oyster or scallop. The two rigid parts of the shell (Figure 4A) are hinged together. The Atlantic geoduck (P. bitruncata), similar to the Pacific species, occurs from the coast of North Carolina to the Gulf of Mexico. Many species, including the quahog, geoduck, and soft-shell clam, are edible. They include clams, oysters, mussels and scallops and most are filter feeders. Omissions? The Bivalvia Gastropods and bivalves may be the most common mollusks, but cephalopods (the family that includes octopuses, squids, and cuttlefish) are by far the most advanced. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. 1ccavanagh. Members of the molluscan class Bivalvia (formerly, Pelecypoda) are known commonly as bivalves and include clams, oysters, mussels, and scallops. STUDY. [53] The Antarctic scallop, Adamussium colbecki, lives under the sea ice at the other end of the globe, where the subzero temperatures mean that growth rates are very slow. But you may not have realized that these creatures are also called bivalves. Class Bivalvia. Professor of Ecology and Biodiversity; Director, Swire Institute of Marine Science, University of Hong Kong. A triangular form, ventral flattening, and secure attachment to firm substrates by byssal threads (byssus; proteinaceous threads secreted by a gland on the foot) have allowed certain bivalves to colonize hard surfaces on wave-swept shores. More than 15,000 living species of bivalves are known, of which about 500 live in fresh water; the others occur in all seas. important members of most marine and freshwater ecosystems. Phylum Mollusca, Class Bivalvia. The valves are connected to one another at a hinge. This article was most recently revised and updated by, clam - Children's Encyclopedia (Ages 8-11), clam - Student Encyclopedia (Ages 11 and up). Articles from Britannica Encyclopedias for elementary and high school students. There are also estuarine bivalves, and two important families, the Unionidae and Corbiculidae, are predominantly freshwater with complicated reproductive cycles. It begins in the Cambrian period (544–505 million years ago [mya]) with a laterally compressed stenothecid monoplacophoran (primitive single-shelled marine mollusk) as the most likely immediate ancestor. In deeper-burrowing species the shells are laterally compressed, permitting more rapid movement through the sediments. The gem clam ( Ref two strong muscles first Edition with your subscription have suggestions to improve this article requires... Lawrence river basins were home to 297 North American species of bivalves is represented by extensive! Is also commonly eaten in broth or chowder ( family Pectinidae ) are hinged together of the class Bivalvia or! And breathing are clams, mussels, oysters, mussels complicated reproductive cycles with close to 80 % being (! And elongated content from our 1768 first Edition with your subscription, rivers and! Species and groups, see ark shell ; coquina clam ; geoduck ; razor.. 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