The Decapoda or decapods are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. 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.
The Glypheoidea, is a group of lobster-like decapod crustaceans which forms an important part of fossil faunas, such as the Solnhofen limestone. These fossils included taxa such as Glyphea, and Mecochirus, mostly with elongated chelipeds. This group of decapods is a good example of a living fossil, or a lazarus taxon, since until their discovery in the 1970s, the group was considered to have become extinct in the Eocene. The superfamily Glypheoidea comprises five families. The two extant species, Neoglyphea inopinata and Laurentaeglyphea neocaledonica, are both in the Glypheidae.
The Majoidea are a superfamily of crabs which includes the various spider crabs.
Hexapodidae is a family of crabs, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae, and was originally described as a subfamily of Pinnotheridae. Its members can be distinguished from all other true crabs by the reduction of the thorax, such that only seven sternites are exposed, and only four pairs of pereiopods are present. Not counting the enlarged pair of claws, this leaves only six walking legs, from which the type genus Hexapus, and therefore the whole family, takes its name. Some anomuran "crabs", such as porcelain crabs and king crabs also have only four visible pairs of legs. With the exception of Stevea williamsi, from Mexico, all the extant members are found either in the Indo-Pacific oceans, or around the coast of Africa.
Eubrachyura is a group of decapod crustaceans comprising the more derived crabs. It is divided into two subsections, based on the position of the genital openings in the two sexes. In the Heterotremata, the openings are on the legs in the males, but on the sternum in females, while in the Thoracotremata, the openings are on the sternum in both sexes. This contrasts with the situation in other decapods, in which the genital openings are always on the legs. Heterotremata is the larger of the two groups, containing the species-rich superfamilies Xanthoidea and Pilumnoidea and all the freshwater crabs. The eubrachyura is well known for actively and constantly building its own burrows. The fossil record of the Eubrachyura extends back to the Cretaceous; the supposed Bathonian representative of the group, Hebertides jurassica, ultimately turned out to be Cenozoic in age.
Erymidae is a family of decapod crustaceans known only from fossils. They survived for 100 million years, from the Permo-Triassic boundary to the Albian. Eleven genera are recognised:
Cheiragonidae is a small family of crabs, sometimes called helmet crabs, placed in its own superfamily, Cheriagonoidea. It comprises three extant species, Erimacrus isenbeckii, Telmessus acutidens and Telmessus cheiragonus, there are no yet evidences of Cheiragonidae in the fossil record. Many of these crabs were formerly treated as members of the Atelecyclidae.
Acantholambrus is an extinct genus of crab. It contains the single species Acantholambrus baumi, and was named by Blow and Manning in 1996.
Matutidae is a family of crabs, sometimes called moon crabs, adapted for swimming or digging. They differ from the swimming crabs of the family Portunidae in that all five pairs of legs are flattened, rather than just the last pair, as in Portunidae. Crabs in the Matutidae are aggressive predators.
Pseudozioidea is a superfamily of crabs, formerly treated in the Eriphioidea, Carpilioidea, Xanthoidea, Pilumnoidea and Goneplacoidea. A number of fossils from the Eocene onwards are known from the family Pseudoziidae. Eleven genera are recognised in three families:
Bechleja is an extinct genus of shrimp which existed during the Eocene period. It contains four species.
The Galatheoidea are a superfamily of decapod crustaceans comprising the porcelain crabs and some squat lobsters. Squat lobsters within the three families of the superfamily Chirostyloidea are not closely related to the squat lobsters within the Galatheoidea. The fossil record of the superfamily extends back to the Middle Jurassic genus Palaeomunidopsis.
Speocarcinus is a genus of crabs in the family Xanthidae, containing six extant species, one fossil species from the Late Miocene, one fossil species from the Eocene (Lutetian) and one fossil species from the Early Eocene (Ypresian):
Pseudophlyctenodes hantkeni is an extinct species of crab in the monotypic genus Pseudophlyctenodes, in the family Xanthidae. It is known from the Eocene of Hungary and Sicily.
Campylonotoidea is a superfamily of shrimp, containing the two families Campylonotidae and Bathypalaemonellidae. Fenner A. Chace considered it to be the sister group to the much larger superfamily Palaemonoidea, with which it shares the absence of endopods on the pereiopods, and the fact that the first pereiopod is thinner than the second. Using molecular phylogenetics, Bracken et al. proposed that Campylonotoidea may be closer to Atyoidea. There are sixteen described species in 3 genera; no fossils are known.
Coleiidae is a family of fossil decapod crustaceans, containing the following genera:
Mathildellidae is family of crabs belonging to the superfamily Goneplacoidea, containing the following genera:
Coeloma is an extinct genus of crabs belonging to the family Mathildellidae. The genus includes 19 species, distributed among several subgenera, and is in need of revision. The fossil record of the genus extends from the Eocene to the Miocene.
Aeger libanensis is a species of fossil prawn belonging to the family Aegeridae. These prawns had very long pereiopods.
The Bulletin de la Société Géologique de France, otherwise known as BSGF - Earth Sciences Bulletin is a peer-reviewed open access scientific journal covering Earth sciences. The journal publishes articles, short communications, reviews, comments and replies. It is published by EDP Sciences and the editor-in-chief is Laurent Jolivet. The journal was established in 1830. It is a publication of the Société géologique de France. Most of the older content, published before 1924 is available online at the Biodiversity Heritage Library.
