Xanthidae is a family of crabs known as gorilla crabs, mud crabs, pebble crabs or rubble crabs. Xanthid crabs are often brightly coloured and are highly poisonous, containing toxins which are not destroyed by cooking and for which no antidote is known. The toxins are similar to the tetrodotoxin and saxitoxin produced by puffer fish, and may be produced by bacteria in the genus Vibrio living in symbiosis with the crabs, mostly V. alginolyticus and V. parahaemolyticus.
Libinia is a genus of crabs in the family Epialtidae, containing twelve extant species:
Portunidae is a family of crabs which contains the swimming crabs.
Majidae is a family of crabs, comprising around 200 marine species inside 52 genera, with a carapace that is longer than it is broad, and which forms a point at the front. The legs can be very long in some species, leading to the name "spider crab". The exoskeleton is covered with bristles to which the crab attaches algae and other items to act as camouflage.
Macrophthalmus is a genus of crabs which are widespread across the Indo-Pacific. It contains the following species :
Parthenopidae is a family of crabs, placed in its own superfamily, Parthenopoidea. It comprises nearly 40 genera, divided into two subfamilies, with three genera incertae sedis:
Ozius is a genus of crabs in the family Menippidae, containing the following species:
Pagurus is a genus of hermit crabs in the family Paguridae. Like other hermit crabs, their abdomen is not calcified and they use snail shells as protection. These marine decapod crustaceans are omnivorous, but mostly prey on small animals and scavenge carrion. Trigonocheirus and Pagurixus used to be considered subgenera of Pagurus, but the former is nowadays included in Orthopagurus, while the latter has been separated as a distinct genus.
The Varunidae are a family of thoracotrematan crabs. The delimitation of this family, part of the taxonomically confusing Grapsoidea, is undergoing revision. For a long time, they were placed at the rank of subfamily in the Grapsidae, but they appear to be closest to Macropthalmus and the Mictyridae, which are usually placed in the Ocypodoidea. It may thus be better to merge the latter superfamily with the Grapsoidea, retaining the latter name as it is older.
Pilumnoidea is a superfamily of crabs, whose members were previously included in the Xanthoidea. The three families are unified by the free articulation of all the segments of the male crab's abdomen and by the form of the gonopods. The earliest fossils assigned to this group are of Eocene age.
Inachidae is a family of crabs, containing 39 genera:
Acanthonyx is a genus of crabs, in the family Epialtidae. Species so far known include:
Leucosiidae is a family of crabs containing three subfamilies and a number of genera incertae sedis:
Actaea is a genus of crabs in the family Xanthidae, containing the following species:
Liomera is a genus of crabs in the family Xanthidae, containing the following species:
Pilumnus is a genus of crabs, containing the following species:
Pisinae is a subfamily of crabs in the family Epialtidae, comprising the following genera:
Inachoididae is a family of crabs originally erected by James Dwight Dana in 1852. It was not recognised as a valid family until the early 1980s. Its members closely resemble those of the family Inachidae, and the Inachoididae could be recognised as a subfamily of that family.
