ABSTRACT
Gall crabs (family Cryptochiridae) are small brachyuran crabs living on or in depressions formed in scleractinian corals. Their adaptation to this unusual habitat has led to specializations, including mucous feeding, small body size, and relatively short appendages. Currently, gall crabs are treated as constituting a distinct superfamily (Cryptochiroidea) that contains the sole family Cryptochiridae. There has never been an attempt to elucidate the relationships of the gall crabs to other brachyurans. The group is therefore an ideal candidate for employing molecular data to deduce phylogenetic relationships. We sequenced a 545-bp fragment of the 16S mitochondrial gene from specimens of a widespread species of cryptochirid (Hapalacarcinus marsupialis) from Mexico and French Polynesia and compared these to other crab sequences available in GenBank. Our preliminary analyses confirm the placement of the cryptochirids in the Brachyura subsection Thoracotremata. Our results also indicate that cryptochirids are members of the superfamily Grapsoidea and are probably closely allied with the family Grapsidae. The Grapsoidea as presently defined is considered a paraphyletic assemblage.
