Brachidontes exustus is a member of the family Mytilidae. It has a thin, fan shaped shell with fine divercating radial ribs. The ribbed surface of the shell is most evident at the outer edges. Umbones are present at the extreme anterior end. The shell can range from blue-gray to yellow to dark brown. The interior has purple-brown blotches with one to four small purplish dysodont hinge teeth (Abbott and Morris 2001, Mekkelsen and Bieler 2008).Species designations in the genus Brachidontes are currently under revision (Berquist et al. 2006). A recent study of the Brachidontes exustus species complex in Florida suggests that there are four cryptic populations with distinct genetic profiles (Lee and O Foighil 2004).