''Cancer'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of marine

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 in the family Cancridae. It includes eight extant species and three extinct species, including familiar crabs of the

littoral zone The littoral zone, also called litoral or nearshore, is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely flood ...

, such as the European edible crab ('' Cancer pagurus''), the Jonah crab (''Cancer borealis'') and the red rock crab ('' Cancer productus''). It is thought to have evolved from related genera in the Pacific Ocean in the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Description

The species placed in the genus ''Cancer'' are united by the presence of a single posterolateral spine (on the edge of the

carapace A carapace is a 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 tortoises, the unde ...

, towards the rear), anterolateral spines with deep fissures (on the carapace edge, towards the front), and a short extension of the carapace forward between the eyes. Their claws are typically short, with grainy or smooth, rather than spiny, keels. The carapace is typically oval, being 58%–66% as long as wide, and the eyes separated by 22%–29% of the carapace width.

Species

The genus ''Cancer'', as currently circumscribed, contains eight extant species: Three fossil species are also included: Also available a
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*'' Cancer fissus'' Rathbun, 1908 – Pliocene, California *'' Cancer fujinaensis'' Sakumoto, Karasawa & Takayasu, 1992 – Miocene, Japan *'' Cancer parvidens'' Collins & Fraaye, 1991 – Miocene, Netherlands As their generic delimitation was based on characters of the dorsal carapace, Schweitzer and Feldmann (2000) were unable to confirm the placement of ''Cancer tomowoi'' in the genus, since it is known only from parts of the sternum and the legs. Other species until recently included in the genus ''Cancer'' have since been transferred to other genera, such as '' Glebocarcinus'', '' Metacarcinus'' and '' Romaleon''.

Taxonomic history

When

zoological nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its formal author, t ...

was first standardised by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in the 1758 10th edition of ', the genus ''Cancer'' included almost all crustaceans, including all the crabs. Linnaeus' cumbersome genus was soon divided into more meaningful units, and ''Cancer'' had been restricted to one group of true crabs by the time of

Pierre André Latreille Pierre André Latreille (; 29 November 1762 – 6 February 1833) was a French zoology, zoologist, specialising in arthropods. Having trained as a Roman Catholic priest before the French Revolution, Latreille was imprisoned, and only regained hi ...

's 1802 work ' ("Natural history in general, and specifically that of crustaceans and insects"). Latreille designated ''C. pagurus'' to be the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

in 1817. In 1975, J. Dale Nations divided the genus ''Cancer'' into four

subgenera In biology, a subgenus ( subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the ge ...

: ''Cancer (Cancer)'', ''Cancer (Glebocarcinus)'', ''Cancer (Metacarcinus)'' and ''Cancer (Romaleon)''. Each of these is now treated as a separate genus, as is the genus '' Platepistoma'', erected by Mary J. Rathbun and resurrected in 1991. Since that time, further genera have been described to accommodate species previously included in ''Cancer'', and the genus ''Cancer'' now contains only eight extant species.

Evolutionary history

The earliest fossils that can be confidently ascribed to the genus ''Cancer'' are those of '' C. fujinaensis'' from the

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

ese

. The genus is therefore thought to have

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

in the northern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

, perhaps during the Miocene, and have spread across that ocean and into the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

by the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

, having crossed the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

and the Straits of Panama.

References

{{Authority control Cancroidea Decapod genera Extant Miocene first appearances