Tivela mactroides
Similar to Tivela byronensis. Tivela mactroides is distinguishable by its distribution from the Carribean to Santa Catarina, Brazil (Rios 2009). Tivela byronensis is found in the Pacific, from lower California to northern Peru (Olsson 1961).
The overall shape is trigonal ovate, and the posterior margin is more pointed than the anterior. The valves are the same 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 distinguished as the animal grows. The lunule is lightly impressed and defined by a very fine groove. The lunule extends up to 3/4 of the anterior dorsal margin, and its width is half its length. The umbo points slightly to the anterior. The escutcheon is not well defined.
The exterior is white with strong coloration in a variety of patterns. There are light brown radial lines in the center of the flank, as well as brown and purple comarginal lines that become more concentrated and deeper in color near the ventral margin. The overlay of the two stripes can result in a plaid pattern. The lunule may be white or outlined in white, and the posterior dorsal margin may be dark brown or dark purple. The interior color is white, but may also have light purple coloration on the posterior and ventral margins.
The ligament is external and extends 1/4 of the posterior dorsal margin. It is supported by rugose nymphal ridges. On the left valve, there are three cardinal teeth (2a, 2b, 4b), and they 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 (3a) and central (1) teeth are not bifid; the traditional posterior tooth (3b) has split into two, and the most posterior half is rugose. There are also two anterior lateral teeth (A1, A3) on the right valve. There is also a fine ridge running parallel to the dorsal posterior margin on both valves, but it is more prominent on the right valve. The adductor muscle scars are similar in area, but the anterior is more elongate and the posterior is rounded. The pallial sinus is rounded and extends to the end of the ligament in length.
Tivela mactroides is found from the Carribean to Santa Catarina, Brazil (Rios 2009).