Gelasimus vomeris is a species of fiddler crab found in the southwest Pacific Ocean.

[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.

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.