The Decapoda or decapods are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns, and shrimp. Most decapods are scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp and Anomura including hermit crabs, porcelain crabs, squat lobsters making up the bulk of the remainder. The earliest fossil decapod is the Devonian Palaeopalaemon.
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.
Calappa is a genus of crabs known commonly as box crabs or shame-faced crabs. The name box crab comes from their distinctly bulky carapace, and the name shame-faced is from anthropomorphising the way the crab's chelae (claws) fold up and cover its face, as if it were hiding its face in shame.
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 :
Maja is a genus of majid crabs erected by Jean-Baptiste Lamarck in 1801. It includes the following extant species:
Upogebia is a genus of mud shrimp, in the family Upogebiidae, containing the following species:
Palaemon is a genus of caridean shrimp of the family Palaemonidae. The conventional circumscription of the genus Palaemon is probably paraphyletic. Molecular data suggest that Palaemonetes, as well as the genera Exopalaemon and Couteriella, are nested within Palaemon. Phylogenetic affinities in these groups correspond better with geographical origin than conventional genus assignments.
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:
Pugettia is a genus of kelp crabs, in the family Epialtidae. It comprises the following species:
Inachus is a genus of crab, 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:
Hyastenus is a genus of crabs in the family Epialtidae, subfamily Pisinae, containing the following extant species:
Leucosia is a genus of crabs in the family Leucosiidae, containing the following extant species:
Ebalia is a genus of crab in the family Leucosiidae.
Rochinia is a genus of crab in the family Epialtidae, containing the following species:
Periclimenaeus is a genus of decapod crustaceans of the family Palaemonidae which is part of the infraorder Caridea. The genus was named by the English carcinologist Lancelot Alexander Borradaile in 1915. He set out the distinguishing features of the genus as:
Body rather stout, cephalothorax deep, a good deal compressed, abdomen greatly curved Thorax without dorsal swelling. Rostrum rather short, compressed, toothed above only. Outer antennular flagellum not deeply cleft. Antennal scale of good breadth. Mandible without palp. Second maxilliped without podopalp. Third maxilliped narrow, with vestigial arthrobranch.
