Gomphina aequilatera
Similar to Gomphina undulosa. Gomphina aequilatera is distinguishable by its round, elongate shape and its smooth nymphs; G. undulosa has a more trigonal shape and rugose nymphs. The lunule of G. undulosa is wider and lanceliform (spear-shaped); whereas, the lunule of G. aequilatera is very narrow. Also, the central tooth (2b) on the left valve if bifid only in G. aequilatera.
The overall shape is elongate ovate. The anterior and ventral margins are rounded, and the posterior margin is short and subtruncated. The anterior dorsal margin is nearly straight, and the posterior dorsal margin is subconvex. The valves are equal in size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines and fine comarginal ribs that become more prominent ventrally. The comarginal ribs may also be slightly stronger at the posterior area of the flank. The lunule is elongate in shape, not impressed, and defined by a fine shallow groove; it extends half the anterior dorsal margin. The umbo is nearly central, and the beaks point slightly to the anterior. The escutcheon is not well defined. The posterior dorsal margin may be slightly raised.
The external color is white or light tan, but other coloration varies. There may be light brown, dark brown or purple comarginal stripes, radial stripes and/or tent marks. Tent marks may be continuous and form comarginal or radial stripes. The umbo may be pink or purple in coloration, or match the rest of the flank. The interior is white.
The ligament is external, extends 1/4 of the posterior dorsal margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth: the anterior (2a) and posterior (4b) teeth are not bifid, and the central tooth (2b) is lightly bifid. The posterior tooth (4b) is fused with the nymph. On the right valve, there are three cardinal teeth: the anterior (3a) is not bifid, and the central (1) and posterior (3b) teeth are lightly bifid. There are no lateral teeth on either valve. The anterior and posterior muscle scars are similar in size and shape. The pallial sinus extends to the posterior end of the nymph in length.