It has a heart-shaped, bivalve shell known as a capitulum which encloses the body and limbs. The capitulum consists of five glossy white, striated calcareous plates. The first pair of plates is positioned at the opening and at the base of the stalk, while the second pair sits farther out, closer to the aperture. The fifth plate (carina) forms a spine that links all the plates together. This shell structure or capitular valve that enables the extension and retraction of six tentacle-like appendages used for feeding, known as cirri.