The hinge is an important feature of the bivalve shell. It joins the two valves, and — importantly — keeps them aligned when the valves close (via the adductor musclesAdductor Muscle:
One of usually two large muscles (one anterior, one posterior) that contract to close the shell of a bivalve and maintain it in that condition; the position of these muscles is usually clearly marked on the shell interior as an adductor muscle scar or impression) or open (via the ligamentLigament:
Elastic uncalcified structure that connects the two bivalve shells at the hinge line and functions as a spring to open the valves when the adductor muscles relax.). It is widely used in taxonomy, and is usually characteristic at the family level. Ask your students to find specimens with the following basic types of bivalve hinges.
TaxodontTaxodont: Example: Ark Shells |
HeterodontHeterodont: Examples: Hard-shelled Clam, Lucine Clam, Crassatella Clam, Kitten’s Paw, Freshwater Mussel |
EdentateEdentate: Examples: Blue Mussel, Soft-shelled Clam, Zebra Mussel |