The many species of Spondylus vary considerably in appearance and range. They are grouped in the same superfamily as the scallops. They are not closely related to true oysters (family Ostreidae); however, they do cement themselves to rocks, rather than attach themselves by a byssus.

Their key characteristic is that the two halves of their shells are joined with a ball-and-socket type of hinge rather than with a toothed hinge, as is more common in other bivalves. They also still retain vestigial anterior and posterior auricles (“ears”, triangular shell flaps) along the hinge line.

Liks scallops, Spondylus spp. have multiple eyes around the edges of their shells, and have relatively well-developed nervous systems. Their nervous ganglia are concentrated in the visceral region, with recognisable optic lobes connected to the eyes.

Spondylus shells are much sought after by collectors, and a lively commercial market exists for them.