Irregularly oval, with flat right valve fitting inside deeper left valve, lower left valve with raised crenulated margins usually higher on one side, moderately compressed, very thin-walled, whitish gray, periostracum easily flaking off; interior dull gray with olive green stain, margin occasionally stained purple, chomata on entire margin or nearly so, anal funnel present. Virginia to Florida, Bermuda, Bahamas, West Indies, Gulf of Mexico, Caribbean Central America, South America (to Argentina). Length 47 mm. Formerly in Ostreola. Compare Crassostrea spp., which have purple ad ductor muscle scars. Note: The habitat of this species is oceanic; Ostrea equestris is the most commonly encountered oyster in the Florida Keys.