__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 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 strong ...

, 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 In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

, subhexagonal,

rectangular In Euclidean geometry, Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a par ...

, 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 biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. 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 ...

endopod The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip (anat ...

is lobed, forming the characteristic portunid lobe. The

cheliped A chela ()also called a claw, nipper, or pinceris a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds. ...

s are usually robust, and in some the last pereiopod pair has ovate dactyls. The sutures of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

between segments 4 to 8 are usually incomplete, and in the

, the eighth sternite 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 The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide i ...

are either all free or the third to fifth are fused, often retaining the sutures though. The first

gonopod Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and millip ...

is strongly curved, with a swollen and strongly hooked base.

Classification

Portunoidea are close relatives of the

Xanthoidea Xanthoidea is a superfamily of crabs, comprising the three families Xanthidae, Panopeidae and Pseudorhombilidae. Formerly, a number of other families were included in Xanthoidea, but many of these have since been removed to other superfamilies. ...

, and the

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

Hexapodidae 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 di ...

and

Mathildellidae Mathildellidae is family of crabs belonging to the superfamily Goneplacoidea, containing the following genera: *'' Beuroisia'' Guinot & Richer de Forges, 1981 *†''Branchioplax ''Branchioplax'' is an extinct genus of crab which existed in Ala ...

, usually included there, are sometimes placed in the Portunoidea, while the deep-sea crabs (

Geryonidae Geryonidae is a family of crabs, including the following genera and species: *'' Chaceon'' Manning & Holthuis, 1989 **'' Chaceon affinis'' (A. Milne-Edwards & Bouvier, 1894) **'' Chaceon albus'' Davie, Ng & Dawson, 2007 **'' Chaceon alcocki'' Gh ...

) are usually placed in the Portunoidea but sometimes in the Xanthoidea. All Portunoidea live in the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

, although the family

Trichodactylidae Trichodactylidae is a family of crabs, in its own superfamily, Trichodactyloidea. They are all freshwater animals from Central and South America, including some offshore islands, such as Ilhabela, São Paulo. Only one of the 50 species is known f ...

, 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 * Carcineretidae (extinct) * Catoptridae *

* Lithophylacidae (extinct) * Longusorbiidae (extinct) * Macropipidae * Pirimelidae *

* Psammocarcinidae (extinct) * Thiidae

References

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