A winged relative of the pearl oysters, with the hinge drawn out at one end into a long backswept spur that gives the genus its name - pteron, wing. The shell is oblique and flattened, dark brown to purplish black outside with faint paler rays, and lined with nacre inside. Length reaches about 10 cm (4 in) including the wing. It hangs from a host by a tuft of byssal threads rather than cementing down, so it can be lifted off intact.
Hosts are almost always upright colonial cnidarians: sea whips, gorgonian sea fans and black coral bushes, with the oyster clamped along a branch and its gape facing into the current. Several individuals often share one colony. This positioning is what a suspension feeder needs - it puts the animal clear of the bottom and into moving water carrying plankton. It occurs on reef slopes and drop-offs from about 5 to 40 m (16 to 130 ft), and was described from 🌊 Red Sea material, which the species name records. The attachment does the host no harm, but it does compete for the same drifting food, and a heavily loaded sea whip bends visibly under the weight of several full-grown oysters. Empty valves stay gripped to the branch by the dried byssus for months afterwards.
- hinge drawn out into a long backswept wing
- hangs from a sea whip or gorgonian by byssal threads
- shell dark brown to purplish, interior pearly
