by wolfe et al., 2019. decapoda dendrobranchiata (prawns) pleocyemata stenopodidea (boxer shrimp) procarididea caridea (true shrimp) reptantia achelata (spiny lobsters, slipper lobsters) polychelida (benthic crustaceans) astacidea (lobsters, crayfish) axiidea (mud shrimp, ghost shrimp, or burrowing shrimp) gebiidea (mud lobsters and mud shrimp) meiura anomura (hermit crabs and others) brachyura (crabs) (crawling/walking decapods) brachyura is separated into several sections, with the basal dromiacea diverging the earliest in the evolutionary history, around the late triassic or early jurassic. the group consisting of raninoida and cyclodorippoida split off next, during the jurassic period. the remaining clade eubrachyura then divided during the cretaceous period into heterotremata and thoracotremata. a summary of the high-level internal relationships within brachyura can be shown in the cladogram below: brachyura dromiacea raninoida cyclodorippoida eubrachyura heterotremata thoracotremata there is a no consensus on the relationships of the subsequent superfamilies and families. the proposed cladogram below is from analysis by tsang et al, 2014: brachyura dromiacea dromioidea dromiidae (may be paraphyletic) dynomenidae homoloidea homolidae (paraphyletic) latreilliidae raninoida raninidae cyclodorippoida cyclodorippidae cymonomidae eubrachyura heterotremata freshwater crabs potamoidea potamonautidae potamidae gecarcinucidae (old world freshwater crabs) pseudothelphusoidea pseudothelphusidae (new world freshwater crabs) trichodactylidae (freshwater crabs) orithyiidae belliidae chasmocarcinidae retroplumidae dorippoidea ethusidae dorippidae leucosiidae majoidea inachidae epialtidae (paraphyletic) majidae / mithracidae corystidae euryplacidae matutidae calappidae parthenopidae cancridae carpiliidae aethridae pseudocarcinus of menippidae menippe of menippidae polybiidae portunidae pilumnoidea tanaochelidae galenidae pilumnidae mathildellidae eriphiidae oziidae vultocinidae trapeziidae goneplacidae scalopidiidae xanthoidea xanthidae (paraphyletic) panopeidae thoracotremata pinnotheridae dotillidae percnidae xenograpsidae cryptochiridae ocypodidae glyptograpsidae grapsidae plagusiidae gecarcinidae sesarmidae mictyridae varunidae macrophthalmidae classification the infraorder brachyura contains approximately 7,000 species in 98 families, as many as the remainder of the decapoda. the evolution of crabs is characterised by an increasingly robust body, and a reduction in the abdomen. although many other groups have undergone similar processes, carcinisation is most advanced in crabs. the telson is no longer functional in crabs, and the uropods are absent, having probably evolved into small devices for holding the reduced abdomen tight against the sternum. in most decapods, the gonopores (sexual openings) are found on the legs. since crabs use their first two pairs of pleopods (abdominal appendages) for sperm transfer, this arrangement has changed. as the male abdomen evolved into a slimmer shape, the gonopores have moved toward the midline, away from the legs, and onto the sternum. a similar change occurred, independently, with the female gonopores. the movement of the female gonopore to the sternum defines the clade eubrachyura, and the later change in the position of the male gonopore defines the thoracotremata. it is still a subject of debate whether a monophyletic group is formed by those crabs where the female, but not male, gonopores are situated on the sternum. superfamilies numbers of extant and extinct (†) species are given in brackets. the superfamily eocarcinoidea, containing eocarcinus and platykotta, was formerly thought to contain the oldest crabs; it is now considered part of the anomura. examples of different crab sectionsdromia personata (dromiacea: dromiidae)ranina ranina (raninoida: raninidae)corystes cassivelaunus (heterotremata: corystidae)ocypode quadrata (thoracotremata: ocypodidae)goneplax rhomboides section †callichimaeroida †callichimaeroidea (1†) section dromiacea †dakoticancroidea (6†) dromioidea (147, 85†) glaessneropsoidea (45†) homolodromioidea (24, 107†) homoloidea (73, 49†) section raninoida (46, 196†) section cyclodorippoida (99, 27†) section eubrachyura subsection heterotremata aethroidea (37, 44†) bellioidea (7) bythograeoidea (14) calappoidea (101, 71†) cancroidea (57, 81†) carpilioidea (4, 104†) cheiragonoidea (3, 13†) corystoidea (10, 5†) †componocancroidea (1†) dairoidea (4, 8†) dorippoidea (101, 73†) eriphioidea (67, 14†) gecarcinucoidea (349) goneplacoidea (182, 94†) hexapodoidea (21, 25†) leucosioidea (488, 113†) majoidea (980, 89†) orithyioidea (1) palicoidea (63, 6†) parthenopoidea (144, 36†) pilumnoidea (405, 47†) portunoidea (455, 200†) potamoidea (662, 8†) pseudothelphusoidea (276) pseudozioidea (22, 6†) retroplumoidea (10, 27†) trapezioidea (58, 10†) trichodactyloidea (50) xanthoidea (736, 134†) subsection thoracotremata cryptochiroidea (46) grapsoidea (493, 28†) ocypodoidea (304, 14†) pinnotheroidea (304, 13†) recent studies have found the following superfamilies and families to not be monophyletic, but rather paraphyletic or polyphyletic: the thoracotremata superfamily grapsoidea is polyphyletic the thoracotremata superfamily ocypodoidea is polyphyletic the heterotremata superfamily calappoidea is polyphyletic the heterotremata superfamily eriphioidea is polyphyletic the heterotremata superfamily goneplacoidea is polyphyletic the heterotremata superfamily potamoidea is paraphyletic with respect to gecarcinucoidea, which is resolved by placing gecarcinucidae within potamoidea the majoidea families epialtidae, mithracidae and majidae are polyphyletic with respect to each other the dromioidea family dromiidae may be paraphyletic with respect to dynomenidae the homoloidea family homolidae is paraphyletic with respect to latreilliidae the xanthoidea family xanthidae is paraphyletic with respect to panopeidae cultural influences a crab divination pot in kapsiki, north cameroon. both the constellation cancer and the astrological sign cancer are named after the crab, and depicted as a crab. william parsons, 3rd earl of rosse drew the crab nebula in 1848 and noticed its similarity to the animal; the crab pulsar lies at the centre of the nebula. the moche people of ancient peru worshipped nature, especially the sea, and often depicted crabs in their art. in greek mythology, karkinos was a crab that came to the aid of the lernaean hydra as it battled heracles. one of rudyard kipling's just so stories, the crab that played with the sea, tells the story of a gigantic crab who made the waters of the sea go up and down, like the tides. the auction for the crab quota in 2019, russia is the largest revenue auction in the world except the spectrum auctions. in malay mythology (as related by hugh clifford to walter william skeat), ocean tides are believed to be caused by water rushing in and out of a hole in the navel of the seas (pusat tasek), where "there sits a gigantic crab which twice a day gets out in order to search for food".: 7–8 the kapsiki people of north cameroon use the way crabs handle objects for divination. the term crab mentality is derived from a type of detrimental social behavior observed in crabs. explanatory notes greek: βραχύς, romanized: brachys = short, οὐρά / οura = tail