Thorny Oyster

The many species of Spondylus vary considerably in appearance. They are grouped in the same superfamily as the scallops, Pectinoidea.

They are not closely related to true oysters (family Ostreidae); however, they do share some habits such as cementing themselves to rocks rather than attaching themselves by a byssus. 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 retain vestigial anterior and posterior auricles ("ears", triangular shell flaps) along the hinge line, a characteristic feature of scallops, although not of oysters.

Spiny oysters are found in all subtropical and (especially) tropical seas, usually close to the coasts. They are filter feeders. The adults live cemented to hard substrates, a characteristic they share, by convergent evolution, with true oysters and jewel boxes. Like the latter, they are protected by spines and a layer of epibionts and, like the former, they can produce pearls. The type of substrate they use depends on the species: many only attach to coral, and the largest diversity of species is found in tropical coral reefs; others like S. spinosus), however, easily adapt to manufactured structures such as boats, pipes, and docks thereby becoming significant invasive species. Some species are also found attached to the shells of other species, perhaps the most common being found attached to the genus Malleus.

Archaeological evidence indicates that people in Neolithic Europe were trading the shells of S. gaederopus to make bangles and other ornaments throughout much of the Neolithic period. The main period of Neolithic use appears to have been from around 5350 to 4200 BC. The shells were harvested from the Aegean Sea, but were transported far into the center of the continent. In the LBK and Lengyel cultures, Spondylus shells from the Aegean Sea were worked into bracelets and belt buckles. Over time, styles changed with the middle Neolithic favouring generally larger barrel-shaped beads and the late Neolithic favoring smaller, flatter and disk-shaped beads. Significant finds of jewelry made from Spondylus shells were made at the Varna Necropolis. The use of Spondylus as grave goods during the late Neolithic appears to have been limited to women and children.