Domecia acanthophora
A rare, tiny reef crab tucked into elkhorn coral branches, most reliably logged around Grand Cayman in warm 25 to 31 C water.
Small, squat crab that wedges itself into the branch forks of elkhorn coral, so you are looking for a shape breaking up the coral's outline rather than an animal out in the open. Body colour runs mottled brown to grey, blending closely with the coral skeleton it lives on. Look for a compact, rounded carapace and short, sturdy claws rather than long spindly legs, and expect it to sit dead still rather than scuttle.
Divers find it wedged motionless in the crooks of elkhorn coral branches, relying on stillness and camouflage rather than fleeing when a torch or lens comes close. It stays put on its coral host rather than roaming the reef, so sightings happen when someone takes the time to scan branch junctions closely instead of swimming past. Given how rarely it is logged, most sightings are the result of a deliberate, patient search rather than a chance encounter.
It lives its whole life associated with elkhorn coral, using the coral's branching structure both as camouflage and as shelter from predators, which makes it one of the clearer examples of a reef species tied to a single coral host.
There is not enough seasonal data to call out particular months, so treat it as a year-round find on Cayman reefs where water sits between roughly 25 and 31 C. Any dive on healthy elkhorn coral is worth a slow look, in any season.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Every logged sighting in the data comes from Grand Cayman in the Cayman Islands, making it the one confirmed place to look for this species. Search elkhorn coral stands on Cayman reef sites specifically, since the crab's presence depends entirely on that coral host being there.
Mapping where Elkhorn Coral Crab is logged…
The only confirmed sightings logged so far are around Grand Cayman in the Cayman Islands. Focus your search on dive sites with healthy stands of elkhorn coral, since this crab lives exclusively within that coral's branches.
There is no detected seasonal pattern, so it is considered a year-round sighting on Cayman reefs where water temperatures range from about 25 to 31 C. Any time you are diving elkhorn coral there is worth a close look.
Look for a small, mottled brown to grey crab wedged into the branch forks of elkhorn coral rather than out in the open. Its compact rounded body and short claws blend with the coral skeleton, so it is often spotted by shape rather than colour contrast.
Exact size data is not available, but like most crabs in the domeciidae family it is small, likely only a centimetre or two across the carapace, easily overlooked among coral branches.
Yes, it is logged as rare at every dive site where it has been recorded. Spotting one usually takes a deliberate, slow search of elkhorn coral branches rather than a casual pass over the reef.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Sally Lightfoot Crab
2,422 sites
