Black lampshells possess a shell that is small to medium in size, with a maximum adult width of 1.38 in (35 mm). The shell is moderately thick with a highly convex shape and a brownish-purple color. The ventral valve narrows to a long and curved beak. There are two spirolophous lophophore spirals, which are dorsally directed and partially supported by crura (hard processes extending forward from the socket region of the dorsal valve) and two pairs of metanephridia. The dorsal floor contains a low median ridge. The slender curved radulifer crura are attached to small outer hinge plates. The pedicle is somewhat short, almost as broad as the foramen, and not used for locomotion. The intestine is curved distally and is enlarged at its end. The adductor muscles possess two attachments on the ventral valve. The mantle canals contain two primary trunks in each mantle lobe. There are no spicules in the soft parts of this lampshell.
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