Bivalves

• With more than 20,000 species broken down into 75 families, the characteristic of the members of this group is that they have two valves joined by a kind of hinge with interconnected teeth. The valves are closed by contracting a powerful muscle.
• The bivalves are the major class of mollusks consumed by man. Among the most important kinds in Venezuela are mussels, mangrove oysters, coquina clams, pismo clams, true tulipas, sand scallops, and pearl oysters.
• The pearl oyster has been of particular importance for Margarita, where pearl oyster fishing starting in the 16th century. Today, they are hardly fished for their pearls, but the pearl oysters themselves are considered a first class food and are eaten either fresh or canned.
• Thanks to the variety of their structures and forms, bivalves can adapt to a wide range of habitats. Some, such as the pismo clam (Tivela mactroides) and the Trachicardium isocarida (a kind of cockle), live buried in the sandy or muddy bottom, which they can dig up with incredible speed. Others spend their lives adhered to hard surfaces -rocks, corals, pieces of wood, shells, and whatever else is to hand- by means of filaments arranged like a tiny, short-trunk tree with the trunk joined to the mollusks shell and the branches (filaments) adhered to the hard surface. This structure is call a "byssus". The mollusks that belong to this type are the mussel (Perna perna), the West Indian turkey wing (Arca zebra), and the pearl oyster (Pintada imbricata). Other species, the mangrove oyster (Crasostrea risophorae), for example, cement themselves to the surface. Lastly, there is another group of bivalves that are borers, like the shipworms. They bore holes in the roots of the mangroves and driftwood and pose a hazard to dock piles and other wooden

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