Macrophthalmus boteltobagoe (Sakai, 1939) is shown to be specifically distinct from M. holthuisi Serène, 1973. The two species differ in many morphological characters and, as well, are shown to prefer different habitats—M. boteltobagoe lives in holes in limestone and scrapes algae for food, whereas M. holthuisi lives on soft mud around mangroves and is a sediment feeder. These different feeding strategies are reflected in the structure and setation of the claws, and in the conformation of the gastric mills.