Limidae: shell equivalve, higher than long, inequilateral, extended obliquely in an anteroventral direction. Dorsal margin with 2 small ears. Trigonal cardinal area with a median ligamental groove. Hinge toothless. A single adductor muscle scar. Pallial line without a sinus. Pectinidae: shell more or less inequivalve, ovate to subcircular with a straight dorsal margin forming wing-like ears.A byssal notch and a ctenolium at right valve.Ligament internal, in a small trigonal pit pointing under the umbones. Hinge without teeth. A single adductor muscle scar. Pallial line without a sinus. Spondylidae: shell stout, usually inequivalve and cemented to substrate by the right valve. Hinge line straight. A trigonal cardinal area, higher in the right valve than in the left. Ligament internal. Hinge with 2 strong teeth and 2 deep sockets in each valve, symmetrically arranged in relation to the internal ligament. A single adductor muscle scar. Pallial line without a sinus.