late 20th century that it was understood that these are in fact very unusual gastropods. Other animals Valves are present in any animal with two or more shell portions connecting at a hinge. Brachiopods are bivalved animals two valves stacked vertically (rather than laterally). The dorsal, or brachial valve hosts the brachial system which supports feeding structures, while the rear end of the ventral, or pedicle valve sends out a fleshy holdfast known as a pedicle. Though each valve has its own symmetrical structure, the two valves have different overall forms and are not mirror images of each other. This distinguishes their valves from those of actual bivalves, which form an identical, but mirrored structure as they are derived from the side of the body. Some crustaceans have a pair of valves which meet at a hinge. These "bivalved crustaceans" include various fossil and living forms, such as ostracods (seed shrimp), conchostracans (clam shrimp), and phyllocarids. References About chitons Mollusc shells Chitons Bivalve anatomy