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Bivalves Why are they called bivalves? • The shells of a bivalve are made up of two halves that are mirror images of each other and are joined at one edge by a flexible hinge. • Each half is asymmetrical and rounded, so that when closed forms a domed space near the hinged edge of the shell which accommodates the bulk of the animal's body. Do Bivalves move? • Oysters and mussels attach themselves to hard surfaces and remain in the same spot for their entire life. They adhere to surfaces using byssal threads secreted by a gland in the foot • Clams bury themselves in sand or sediment on the seafloor or in riverbeds. Some just below the surface, others bury deep. – They may have spines that help to secure them in the sediment and to prevent predators from dislodging them. • Boring bivalves have thin, soft shells that are armed with a hard tip. They bore into solid surfaces such as wood or rock. • Free-moving bivalves such as scallops use their muscular foot to dig into sand and soft sediments. They can also move through the water by opening and closing their valves, an action that pushes them through the water. Swimming Scallops • http://www.bbc.co.uk/nature/life/Pectinidae# intro How do bivalves breathe? • Most bivalves have a pair of large gills which are located in their mantle cavity. – enable them to extract oxygen from the water (to breathe) and to capture food. – Water is drawn into the mantle cavity and washes through the gills. – In species that burrow, a long siphon is extended to the surface to take in water. How do bivalves eat? • Mucus on the gills helps capture food and cilia transfer the food particles to the mouth. • Once in the mouth, food passes into the stomach to be digested. Parts of a bivalve • Bivalves have a mouth, heart, intestine, gills, stomach and siphon • They have an adductor muscle that, when contracted, holds the two halves of the shell closed. • Bivalves have a muscular foot, which in many species such as clams, is used to anchor their body to the substrate or dig down into the sand. • They do not have a head, radula or jaws. Killer Clams??? • http://www.blueworldtv.com/webisodes/watc h/killer-clams Mollusks Quiz on Monday! • Defining characteristics of each class of mollusks and exceptions • Body parts and their function (radula, siphon, tentacles, operculum, byssal threads, foot) • Body systems (Reproductive, Circulatory, Nervous)