Hexapodidae
Encyclopedia
Hexapodidae is a family
of crab
s, 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 claw
s, this leaves only six walking legs, from which the type genus Hexapus, and therefore the whole family, takes its name. Some anomura
n "crabs", such as porcelain crab
s and king crab
s 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
.
, with unverified reports of a species in the Maastrichtian
of Senegal
.
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...
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, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae
Goneplacidae
Goneplacidae is a family of crabs of the order Decapoda and the superfamily Goneplacoidea. It includes the following genera:*† Amydrocarcinus Schweitzer, Feldmann, Gonzáles-Barba & Vega, 2002*Bathyplax A. Milne-Edwards, 1880*Carcinoplax H...
, and was originally described as a subfamily of Pinnotheridae
Pinnotheridae
Pinnotheridae is a family of pea crabs. Pea crabs are tiny soft-bodied crabs that live commensally in the mantles of certain bivalve molluscs...
. Its members can be distinguished from all other true crabs by the reduction of the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
, such that only seven sternites are exposed, and only four pairs of pereiopods are present. Not counting the enlarged pair of claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
s, this leaves only six walking legs, from which the type genus Hexapus, and therefore the whole family, takes its name. Some anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
n "crabs", such as porcelain crab
Porcelain crab
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices...
s and king crab
King crab
King crabs, also called stone crabs, are a superfamily of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food, the most common being the red king crab, Paralithodes camtschaticus.King...
s also have only four visible pairs of legs. With the exception of Stevea williamsi, from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, all the extant members are found either in the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
oceans, or around the coast of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
.
Fossil record
In addition to the extant taxa, the family contains two genera known only from fossils – Goniocypoda and Palaeopinnixa – and two further genera include both living and fossil representatives: Hexapus and Stevea. The family's fossil record extents back certainly as far as the PaleocenePaleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
, with unverified reports of a species in the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
of Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
.