Sunetta donacina
Similar to Sunetta seminuda. Sunetta donacina is distinguishable by its smooth flank, or in specimens with ribs, the ribs extend the entire flank. Sunetta seminuda has ribs at the posterior and central areas of the flank, and a smooth anterior area.
The overall shape is elongate, ovate, and the anterior is slightly more pointed than the posterior. The anterior dorsal margin is straight to slightly concave. The posterior half of the flank is slightly more inflated than the anterior. The valves are the same size and shape (equivalve), and there is no gape when they are closed. The sculpture consists of growth lines only, sometimes with faint commarginal ribs that become stronger posteriorly. The lunule is lightly impressed, defined by a fine shallow groove, and extends half the anterior dorsal margin. The umbo points slightly forward. The escutcheon is deeply sunken.
The exterior color is white and can have a variety of colorations and patterns. There may be light brown, dark brown or purple comarginal stripes and/or tent marks. Typically, one pattern dominates the flank. The lunule may be marked by purple, light or dark brown. The internal color is white, and there may be purple coloration along the growth lines or in the umbonal cavity.
The ligament is external and supported by nymphal ridges. On the left valve, there are three cardinal teeth. The teeth (2a, 2b, 4b) are not bifid, the anterior (2a) tooth is very weak, 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. The anterior tooth (3a) is very weak, 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 fine crenulations along the internal margins. The anterior and posterior muscle scars are similar in size and shape. The pallial sinus is rounded and extends to the end of the nymph in length.