Squareback marsh crab

Armases cinereum

Family Sesarmidae - Marsh crabs

Carapace squarish; lateral sides straight with no lateral teeth; color brown with some darker markings; claws with white fingers, brown on upper surface of movable finger, tips of both fingers dark; surface of outer mouth part with oblique hairy ridge; no tooth behind the outer eye tooth; fourth walking leg with black spines on upper and lower surfaces; male claws grow larger than female claws; small tubercles (bumps) on upper surface of movable finger;
Similar Species
The mangrove marsh crab (Sesarma curacaoense) and the purple marsh crab (S. reticulatum) have a tooth behind the outer orbital tooth. The humic marsh crab (A. ricordi) is orange to reddish brown and lacks the bumps on the upper movable finger.
Bay, intertidal or above tidal zone, rocks and marshes, sandy bottoms
Maximum Size
2 1/2 cm (1 in)
Other Common Names
Previous Scientific Names
Sesarma cinereum
Squareback marsh crabs live in a marine environment but do not require seawater to survive, making them true terrestrial crabs. They still need a source of water, though, for oxygen exchange across its gills.