Common name : spiny or thorny oysters

Aspect : very thick, robust, and heavy shells; strongly inequivalve, the lower valve is deeply cupped and attached to hard substrates whereas the upper valve is flatter; inequilateral form due to vestigial anterior and posterior auricles (small triangular flaps) along the hinge line; covered with long, spiny or lamellar projections, giving a rough, ornate appearance; highly variable colors (reds, purples, oranges, whites, and combinations, often vivid in living specimens); the strong hinge is unique, featuring a ball-and-socket articulation rather than traditional teeth; typical adult size is 8–15 cm (maximum size ≈ 20–25 cm)

Feeding : filtration of microorganisms in suspension (phytoplankton, zooplankton, detritus, and organic particles)

Environment : mostly tropical and subtropical regions, especially in the Indo-Pacific; some species occur in the eastern Atlantic and Mediterranean; they are cementing bivalves that attach directly to hard substrates such as rocks, corals, coral rubble, or even human-made structures like docks and pipes; from shallow subtidal zones to deeper waters (~5–200 m depending on species)