An old Dutch microscopist, Anton von Leeuwenhoek, in 1675, while studying with lenses of his own manufacture, discovered and described forms which undoubtedly belong to this genus. A, B, Megastoma entericum, C, Balantidum entozoon.
The outline of the body is more nearly rectangular than in other Flat-fishes from the obtuseness of the snout and caudal end, and the somewhat uniform breadth of the body. The surface is rough from the presence of long slender spines on the scales. There is a large perforation in the septum between the gill cavities, but this occurs also in Arnoglossus megastoma, which is placed in another genus.