About Isognomon alatus (Gmelin, 1791)
Isognomon alatus, commonly called the flat tree oyster, has two thin, irregularly shaped valves connected by a long, straight hinge. The outer shell surface is textured with numerous rough concentric rings that bear loose flakes, and its colour ranges from pale brownish olive to purplish black. The inner nacre is lustrous, cream-coloured, and shaded with purplish brown. This oyster attaches itself to its substrate with a byssus thread, and reaches a length of 75 to 95 millimetres (3.0 to 3.7 in).
The flat tree oyster is distributed across southern Florida, the Caribbean Sea, the Gulf of Mexico, Colombia, Costa Rica, Cuba, Jamaica, the Lesser Antilles, Puerto Rico, Venezuela, San Andrés, and Brazil. It is one of three closely related species that grow, sometimes in dense patches, on mangrove roots (especially those of the red mangrove Rhizophora mangle) and shallow rocky areas, at depths down to 15 metres (49 ft) or more. On coral reefs, it grows on rock ledges and exposed rocks in high-sedimentation areas, forming mats that contain hundreds of individual oysters. It can also grow on the shells of the Atlantic thorny oyster Spondylus americanus.
