Sunetta seminuda
Similar to Sunetta donacina. Sunetta seminuda can be distinguishable by its comarginal ribs that cover the posterior and central area of the flank; the anterior is smooth. Sunetta donacina typically has a smooth flank, but in specimens with comarginal ribs, the ribs cover the entire flank.
The overall shape is elongate, ovate. The anterior dorsal margin is slightly concave. The posterior end is slightly truncated; whereas, the anterior end is rounded. The posterior half of the flank is slightly more inflated than the anterior. The valves are the same size and shape (equivalve), and there are no gapes when they are closed. The sculpture consists of growth lines and comarginal, rounded ribs that span only the posterior and middle of the flank; the anterior is smooth. The lunule is lightly impressed, defined by a fine shallow groove, and extends half the anterior dorsal margin. The umbo is subcentral, and the escutcheon is deeply sunken.
The external surface is white or light tan, and can have brown tent marks on all or part of the flank. The interior is white.
The ligament is external, extends 1/3 of the posterior dorsal margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth. The teeth (2a, 2b, 4b) are not bifid, and the posterior tooth (4b) is fused with the nymph. There is also one anterior lateral tooth (A2) on the left valve. On the right valve, there are three cardinal teeth. The teeth (3a, 1, 3b) are not bifid, and the posterior tooth (3b) is fused with the nymph. There are also two anterior lateral teeth (A1, A3) on the right valve. There are crenulations on the posterior and ventral margins, and finer crenulations on the anterior ventral margin. The anterior and posterior muscle scars are the same size and shape. The pallial sinus is rounded and reaches the posterior tooth in length.