Isognomon alatus, also called the Mangrove Oyster, forms large compact colonies or "oyster bars" on dock pilings and cement seawalls in the Florida Keys (here on a PVC piling at Ramrod Key). The extreme flatness of the isognomonid shell valves has been interpreted as an adaptation that minimizes resistance to strong water flow. The family Isognomonidae is known since the Permian Period, is represented by 2 living genera and ca. 20 species, distributed worldwide in shallow subtropical and tropical seas, from shallow to abyssal depths. Isognomon alatus is eaten in Jamaica as a substitute for the dwindling populations of harvestable oysters (Ostreidae). Isognomonids are often called “tooth pearl shells” because of their prominent multivincular ligaments and nacreous interior shell surfaces.