Tivela delessertii
The overall shape is trigonal ovate, and the anterior margin may be slightly more pointed than the posterior. The valves are the same size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines. The lunule is lightly impressed and defined by a fine shallow groove; the lunule extends up to 3/4 of the anterior dorsal margin. The umbones are central and the beaks point to each other. The escutcheon is lightly impressed, but otherwise not well defined.
The exterior color is white. There can be a variety of light brown patterns, including comarginal stripes, radial stripes and/or tent marks. The interior color is white, and can have a variety of brown or purple colorations. There may be rays of brown or purple originating in the umbonal cavity and spanning the middle of the interior. The color can also be concentrated in the umbonal cavity or pallial sinus.
The ligament is external, spans 1/4 of the dorsal posterior margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth (2a, 2b, 4b); the cardinal teeth are not bifid. There is also one anterior lateral tooth (A2) on the left valve. On the right valve, there are four cardinal teeth. The anterior tooth (3a) is very weak and not bifid. The central tooth (1) is not bifid. The traditional posterior tooth (3b) has split into two teeth; the most posterior is rugose and fused with the nymph. There are also two anterior lateral teeth (A1, A3) on the right valve. The anterior and posterior adductor muscles are similar in size and shape. The pallial sinus is rounded and extends to the posterior tooth in length.
Tivela delessertii is found from lower California to Panamal; it is most commonly found in Acapulco, Mexico (Olsson 1961).