The body color is gray-brown, with brown lines on the carapace and transverse striae on the abdomen.

[3] The front pairs of legs are long, but the hind legs are shorter and are used to carry on the back a variety of objects and organisms, especially valves of bivalves, by which these crabs camouflage and protect themselves.

[5] They mainly feed on small organisms and decaying flesh of dead animals.

[6][7] These crabs live on sandy substrate and muddy bottom, from a few meters up to 75 m deep.

[4] Under hypoxic conditions, Ethusa mascarone has been observed to discard its objects of camouflage "to either increase mobility and/or reduce oxygen demand".