Gelasimus vomeris is a species of fiddlercrab found in the southwest Pacific Ocean. In Australia, it is found in the east and north from Darwin to Sydney.[1]
It is commonly known as the two-toned fiddler crab, orange-clawed fiddler crab or Southern calling fiddler crab, however the common name orange-clawed fiddler crab is also used for the fiddler crab Tubuca coarctata.[2] Previous binomial names include Uca vomeris and Uca vocans vomeris.
The carapace is up to 30 mm across,[3] black-brown with blue patches to varying extent. Adult males have an enlarged claw with a grey or pink upper finger, and orange lower finger and hand.[3] Like other fiddler crabs the claw is used to scare or fight other males, and in waving displays to attract females. The lower male claw has a large triangular protection in the most distant part from the body.[4]
If caught, the colors of Gelasimus vomeris crabs will become less brilliant within minutes,[5] and in response to the presence of predators in an area, the blue color of these fiddler crabs will change over a few days to a dull muddy brown.[6]
Distribution and habitat
The preferred habitat of these crabs is unshaded sandy mud. They are found in bays, estuaries and creeks,[1] living in burrows at lower tide levels which they stay close to, typically <1 m while feeding.[7] There is a predominance of right handed individuals in colonies, one study finding left handed individuals forming only 1.4% of the study population.[8]
