Philobryidae

Philobryidae is a taxonomic family of very small equivalved triangular saltwater clams, marine bivalve molluscs, related to the ark clams and the bittersweets. Their shells have projecting umbones and are non-nacreous. The ligament of the hinge is either completely internal or only slightly external. They have only one adductor muscle scar on the inside of each of their shells as opposed to the more-common two. Species from this family are found in most seas, in shallow to moderately deep water. This family contains about sixty species in seven genera.