Gall crabs are cryptochirid crabs that burrow and live their entire lives within cavities they create in stony corals. While many of us have probably introduced corals with gall crabs in them, few of us may have noticed them because these crustaceans are tiny and cryptic (hence their name, Cryptochiridae). If your reef tank is stocked with stony corals (LPS and SPS alike), there’s a good possibility that you have gall crabs. If you see any strange cavities or bumps on a stony coral, take a closer look. If you see a little tick-like critter inside, you’ve got yourself a gall crab. These little guys are fairly harmless hitchhikers.
Fizesereneia panda (pictured above) is the newest described species of gall crabs. It is only one of two known cryptochirids from the Red Sea, and it was named for its “panda face” pattern on its head. F.panda is only currently known to burrow in Lobophyllia cf.hemprichii, L.cf.corymbosa, and Symphyllia recta brain corals.
Interesting factoid: Some faster growing corals can completely grow over the openings gall crabs create … permanently entombing the crab inside!