Portunoidea
Encyclopedia
Portunoidea is a superfamily
of crab
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 analyses.
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's endopod is lobed, forming the characteristic portunid lobe. The chelipeds are usually robust, and in some the last pereiopod pair has ovate dactyl
s. The sutures of the sternum
between segments 4 to 8 are usually incomplete, and in the Portunidae
, the eighth sternite is usually visible if seen from below and has a penial groove.
In males, the abdominal 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.
, 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
.
According to the latest synopsis, there are eleven families in the superfamily Portunoidea, four of which are extinct:
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
of crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s that includes the family Portunidae
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...
, the swimming crabs. Which other crab families are also placed here is a matter of some contention, and may be revised following molecular phylogenetic analyses.
Description
Their rather flat and smooth carapaceCarapace
A carapace is a dorsal 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 tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
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
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
.
In some, the first maxilliped's endopod is lobed, forming the characteristic portunid lobe. The chelipeds are usually robust, and in some the last pereiopod pair has ovate dactyl
Dactyl
Dactyl may refer to:* Dactyl , a creature in Greek mythology* Dactyl , a metrical foot consisting of one long syllable and two short* Dactyl , the small natural satellite orbiting the asteroid Ida...
s. The sutures of the sternum
Sternum (arthropod)
The sternum is the ventral portion of a segment of an arthropod thorax or abdomen.In insects, the sterna are usually single, large sclerites, and external...
between segments 4 to 8 are usually incomplete, and in the Portunidae
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...
, the eighth sternite is usually visible if seen from below and has a penial groove.
In males, the abdominal 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 XanthoideaXanthoidea
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. These include Carpilioidea, Eriphioidea, Hexapodoidea,...
, and the families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Hexapodidae
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...
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
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
, although the family Trichodactylidae
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 from the fossil record, Sylviocarcinus piriformis from...
, sometimes included here, live in fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
.
According to the latest synopsis, there are eleven families in the superfamily Portunoidea, four of which are extinct:
- Carcinidae
- CarcineretidaeCarcineretidaeCarcineretidae 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 in having some paddle-shaped pereiopods...
(extinct) - Catoptridae
- Geryonidae
- Lithophylacidae (extinct)
- Longusorbiidae (extinct)
- Macropipidae
- Pirimelidae
- PortunidaePortunidaePortunidae 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...
- Psammocarcinidae (extinct)
- Thiidae