Hexapodidae is a
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
of
crab
Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...
s, the only family in the superfamily Hexapodoidea.
It has traditionally been treated as a
subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
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
The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen.
In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...
, such that only seven
sternites are exposed, and only four pairs of
pereiopods are present.
Not counting the enlarged pair of
claws, this leaves only six walking legs, from which the type genus ''Hexapus'', and therefore the whole family, takes its name. Some
anomura
Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word ''crab'', all true crabs are in the sister group to the Anomura, the Brachyura (the two groups ...
n "crabs", such as
porcelain crabs and
king crabs also have only four visible pairs of legs. With the exception of ''
Stevea williamsi'', from
Mexico
Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
, all the extant members are found either in the
Indo-Pacific
The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
oceans, or around the coast of
Africa
Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
.
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
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
, with unverified reports of a species in the
Maastrichtian
The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
of
Senegal
Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...
.
Genera
The following are the
genera
Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
included under Hexapodidae:
:
Genera marked with are extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
*''
Bellhexapus''
De Angeli, Guinot, & Garassino, 2010
*''
Eohexapus''
De Angeli, Guinot, & Garassino, 2010
*''
Eurohexapus''
De Angeli, Guinot, & Garassino, 2010
*''
Globihexapus''
Schweitzer & Feldmann, 2001
*''
Goniocypoda''
Woodward, 1867
*''
Hexalaughlia''
Guinot, 2006
*''
Hexapinus''
Manning & Holthuis, 1981
*''
Hexaplax''
Doflein, 1904
*''
Hexapus''
De Haan, 1833
*''
Mariaplax''
Rahayu & Ng, 2014
*''
Lambdophallus''
Alcock, 1900
*''
Latohexapus''
Huang, Hsueh, & Ng, 2002
*''
Paeduma''
Rathbun, 1897
*''
Palaeopinnixa''
Via, 1966
*''
Parahexapus''
Balss, 1922
*''
Pseudohexapus''
Monod, 1956
*''
Rayapinus''
Rahayu & Ng, 2014
*''
Spiroplax''
Manning & Holthuis, 1981
*''
Stevea''
Manning & Holthuis, 1981
*''
Thaumastoplax''
Miers, 1881
*''
Theoxapus''
Rahayu & Ng, 2014
*''
Tritoplax''
Manning & Holthuis, 1981
References
{{Taxonbar, from=Q1061024
Crabs
Extant Paleocene first appearances
Taxa named by Edward J. Miers
Decapod families