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Cancer (genus)
Encyclopedia
Cancer is a genus
of marine crab
s in the family Cancridae
. It includes 8 extant species and 3 extinct species, including familiar crabs of the littoral zone, 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
.
, 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.
of , Cancer included most of the larger crustacean
s, including all the crabs. Later authors divided it into an increasing number of genera, and the genus Cancer, as currently circumscribed
, contains only eight extant species:
Three fossil species are also included:
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
.
ese Miocene
. The genus is therefore though to have evolved
in the northern Pacific Ocean
, perhaps during the Miocene, and have spread across that ocean and into the Atlantic Ocean
by the Pliocene
or Pleistocene
, having crossed the equator
and the Straits of Panama.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of marine 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 in the family Cancridae
Cancridae
Cancridae is a family of crabs. It comprises six extant genera, and eleven exclusively fossil genera, in two subfamilies:Cancrinae Latreille, 1802*Anatolikos Schweitzer & Feldmann, 2000*†Anisospinos Schweitzer & Feldmann, 2000...
. It includes 8 extant species and 3 extinct species, including familiar crabs of the littoral zone, such as the European edible crab (Cancer pagurus), the Jonah crab
Jonah crab
The Jonah crab, Cancer borealis, is a species of crab found on the Atlantic coast of North America. It is closely related to the Dungeness crab of the Pacific coast, and is known for its strong claws, although it is not a very aggressive species. It has been fished on a small scale since the 1970s,...
(Cancer borealis) and the red rock crab (Cancer productus
Cancer productus
Cancer productus, one of several species known as the red rock crab, is a crab of the genus Cancer found on the western coast of North America.- Description :...
). It is thought to have evolved from related genera in the Pacific Ocean in the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
.
Description
The species placed in the genus Cancer are united by the presence of a single posterolateral spine (on the edge of the 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...
, 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
When originally named as a genus by Carl Linnaeus in the 1758 10th edition10th edition of Systema Naturae
The 10th edition of Systema Naturae was a book written by Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature...
of , Cancer included most of the larger crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, including all the crabs. Later authors divided it into an increasing number of genera, and the genus Cancer, as currently circumscribed
Circumscription (taxonomy)
In taxonomy, circumscription is the definition of the limits of a taxonomic group of organisms. One goal of taxonomy is to achieve a stable circumscription for every taxonomic group. Achieving stability can be simple or difficult....
, contains only eight extant species:
- Cancer bellianusCancer bellianusCancer bellianus, the toothed rock crab, is a common species of crab in the north-eastern Atlantic Ocean.-Description:It grows up to in carapace length, and is pale brown with red spots.-Distribution and ecology:...
Johnson, 1861 – toothed rock crab - Cancer borealisJonah crabThe Jonah crab, Cancer borealis, is a species of crab found on the Atlantic coast of North America. It is closely related to the Dungeness crab of the Pacific coast, and is known for its strong claws, although it is not a very aggressive species. It has been fished on a small scale since the 1970s,...
Stimpson, 1859 – Jonah crab - Cancer irroratusCancer irroratusCancer irroratus, common name the Atlantic rock crab, or peekytoe crab, is a crab in the genus Cancer. Other local names are Maine crab, bay crab, sand crab and mud crab. It has nine marginal teeth on the front edge of the carapace beside each eye....
Say, 1817 – Atlantic rock crab - Cancer johngarthiCancer johngarthiCancer johngarthi is a species of crab that lives in the eastern Pacific Ocean from Mexico to Panama. It was separated from C. porteri in 1989, and is the subject of a small-scale fishery off Baja California.-Distribution:...
Carvacho, 1989 - Cancer pagurus Linnaeus, 1758 – edible crab
- Cancer plebejus Poeppig, 1836
- Cancer porteri Rathbun, 1930
- Cancer productusCancer productusCancer productus, one of several species known as the red rock crab, is a crab of the genus Cancer found on the western coast of North America.- Description :...
J. W. Randall, 1840 – red rock crab
Three fossil species are also included:
- 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
Glebocarcinus
Glebocarcinus is a genus of crabs formerly included in the genus Cancer, containing two species:*Glebocarcinus oregonensis *Glebocarcinus amphioetus...
, Metacarcinus
Metacarcinus
Metacarcinus is a genus of crabs formerly included in the genus Cancer. It includes nine exclusively fossil species and five extant species, of which four are also known from the fossil record...
and Romaleon
Romaleon
Romaleon is a genus of marine crabs formerly considered in the genus Cancer.-Species:The genus, as currently circumscribed, contains seven species:*Romaleon antennarium Stimpson, 1856*Romaleon branneri Rathbun, 1926...
.
Evolutionary history
The earliest fossils that can be confidently ascribed to the genus Cancer are those of C. fujinaensis from the JapanJapan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
. The genus is therefore though to have evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
in the northern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, perhaps during the Miocene, and have spread across that ocean and into the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
by the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
or Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, having crossed the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
and the Straits of Panama.