__NOTOC__ Portunoidea is a

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

s that includes the family Portunidae, the swimming crabs. Which other crab families are also placed here is a matter of some contention, and may be revised following

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analyses.

Description

Their rather flat and smooth

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

is usually wider than long and of hexagonal, subhexagonal, rectangular, or transversely ovate shape. It is usually widest between the hindmost spines of the forward rim; there may be up to 9 pairs of these spines, with a few smaller ones right above the head, but they are missing altogether in some species. In some, the first

maxilliped An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

's endopod is lobed, forming the characteristic portunid lobe. The chelipeds are usually robust, and in some the last

pereiopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...

pair has ovate dactyls. The sutures of the sternum between segments 4 to 8 are usually incomplete, and in the Portunidae, the eighth

sternite The sternum (pl. "sterna") is the ventral portion of a segment of an arthropod thorax or abdomen. In insects, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the ...

is usually visible if seen from below and has a penial groove. In males, the

abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

somites are either all free or the third to fifth are fused, often retaining the sutures though. The first gonopod is strongly curved, with a swollen and strongly hooked base.

Classification

Portunoidea are close relatives of the Xanthoidea, and the families Hexapodidae and Mathildellidae, usually included there, are sometimes placed in the Portunoidea, while the deep-sea crabs ( Geryonidae) are usually placed in the Portunoidea but sometimes in the Xanthoidea. All Portunoidea live in the ocean, although the family Trichodactylidae, sometimes included here, live in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

. According to the latest synopsis, there are eleven families in the superfamily Portunoidea, four of which are extinct: *

Carcinidae Carcinidae is a family of crabs belonging to the order Decapoda. It has four subfamilies, including Pirimelinae which was previously treated as a family. Taxonomy The family as currently circumsribed includes four subfamilies and eight genera, s ...

Carcineretidae Carcineretidae is a prehistoric family of heterotrematan crustaceans. They are only known from Cretaceous fossils. These crabs are tentatively placed in the superfamily Portunoidea and resemble the swimming crabs (Portunidae) in having som ...

(extinct) *

Catoptridae Portunidae is a family of crabs which contains the swimming crabs. Description Portunid crabs are characterised by the flattening of the fifth pair of legs into broad paddles, which are used for swimming. This ability, together with their stro ...

* Geryonidae * Lithophylacidae (extinct) * Longusorbiidae (extinct) *

Macropipidae Portunidae is a family of crabs which contains the swimming crabs. Description Portunid crabs are characterised by the flattening of the fifth pair of legs into broad paddles, which are used for swimming. This ability, together with their stro ...

Pirimelidae Pirimelinae is a subfamily of crabs belonging to the family Carcinidae in the order Decapoda The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as ...

* Portunidae * Psammocarcinidae (extinct) *

Thiidae Thiidae is a family of crabs in the crustacean order Decapoda. Genera The family contains two genera in two subfamilies: * Subfamily Nautilocorystinae Ortmann, 1893 ** '' Nautilocorystes'' Milne Edwards, 1837 * Subfamily Thiinae Dana, 1852 ...

References

{{Taxonbar, from=Q1337809 Arthropod superfamilies Taxa named by Constantine Samuel Rafinesque