The shell morphology and anatomy of the micro bivalve Epilepton clarkiae is described from specimens collected in NW Ireland. Anatomical features of a very large subtriangular hypobranchial gland, a pedal protractor bisecting the anterior adductor muscle, a byssus gland divided into symmetrical left and right halves, gills represented by a single demibranch and paired seminal receptacles indicate that the genus Epilepton is most correctly placed in the superfamily Galeommatoidea, and family Montacutidae with closest similarities to the genera Litigiella, Jousseaumiella, and Mioerycina. The genus Potidoma is confirmed to be congeneric with Epilepton. Epilepton clarkiae is a commensal with sipunculans with the specimens examined here associated with Phascolosoma granulatum. The geographic range is from the Mediterranean to southern Scandinavia.