A banded, black anomuran crab that scurries about oyster clumps and sponges. Dorsoventrally compressed, it looks as if it were squashed with a hammer, enabling it to hide in crevices. Petrolisthes is a master of escape, camouflage and autotomizing. And it also is a magnificent filter feeder; it rhythmically waves its long flattened mouth parts like a barnacle sweeping the water. Size: 2-3 cm.