Arrow Crab Stenorhynchus spp. In immature reefs, those containing NO corals or other inverts, Arrow Crabs have been known to take care of fire or bristle worms. Their sexual differentiation varies by species. In S. lanceolatus the female is dramatically smaller than the male. In S. seticoris the male has a triangular folded abdomen plate, and the female has the rounded abdomen plate.
Size is also a variable, dependent upon the origin of the animal.
Females may be dramatically smaller. Different species inhabit different parts of the world. The most common Arrow Crab comes from the Caribbean, but other species are imported from the Indo-Pacific region, eastern Africa, and California. They normally inhabit portions of the reef usually associated with a small cave or crevice. Breeding in the aquarium is not generally successful.