A fiddler crab, sometimes known as a calling crab, may be any of more than one hundred species of semiterrestrial marine crabs in the family Ocypodidae. A smaller number of ghost crab and mangrove crab species are also found in the family Ocypodidae. This entire group is composed of small crabs, the largest being slightly over two inches (5 cm) across. Fiddler crabs are found along sea beaches and brackish intertidal mud flats, lagoons and swamps. Fiddler crabs are most well known for their sexually dimorphic claws; the males' major claw is much larger than the minor claw, while the females' claws are both the same size.
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.
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 :
Charybdis is a genus of swimming crabs in the family Portunidae; "Charybdis" is Greek for whirlpool.
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.
Actumnus is a genus of crabs in the family Pilumnidae. Alongside the 28 extant species, it has a fossil record extending back into the Miocene.
Etisus is a genus of crabs, containing the following extant species:
Epialtinae is a subfamily of crabs, containing the following genera:
Actaea is a genus of crabs in the family Xanthidae, containing the following species:
Chlorodiella is a genus of crabs in the family Xanthidae, containing the following species:
Pilodius 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:
Pseudoliomera is a genus of crabs in the family Xanthidae, containing the following species:
Xanthias is a genus of crabs in the family Xanthidae, containing two exclusively fossil species and the following extant species:
Lophozozymus is a genus of crabs in the family Xanthidae, 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.
