Cancer (genus)
A genus of marine crabs including the European edible crab.
Cancer is a genus of marine crabs belonging to the family Cancridae. It comprises eight living species and three fossil species, among them well-known crabs found in the littoral zone, like the European edible crab (Cancer pagurus), the Jonah crab (Cancer borealis), and the red rock crab (Cancer productus).
Members of the genus Cancer share several physical traits: a single posterolateral spine on the rear edge of the carapace, anterolateral spines with deep fissures along the front edge, and a short forward projection of the carapace between the eyes. Their claws are usually short, with grainy or smooth keels rather than spiny ones. The carapace is typically oval in shape, measuring 58% to 66% as long as it is wide, and the eyes are separated by 22% to 29% of the carapace width.
The currently recognized species within Cancer include eight extant forms. Three fossil species are also placed here: Cancer fissus (Pliocene, California), Cancer fujinaensis (Miocene, Japan), and Cancer parvidens (Miocene, Netherlands). Because the genus was originally defined based on dorsal carapace features, the placement of Cancer tomowoi remains uncertain—it is known only from sternum and leg fragments. Other species once included in Cancer have since been moved to genera such as Glebocarcinus, Metacarcinus, and Romaleon.
In taxonomic history, when Carl Linnaeus standardized zoological nomenclature in 1758, the genus Cancer encompassed nearly all crustaceans, including every crab. This unwieldy group was soon split into more meaningful units, and by Pierre André Latreille’s 1802 work, Cancer had been restricted to a single group of true crabs. Latreille designated Cancer pagurus as the type species in 1817. In 1975, J. Dale Nations subdivided Cancer into four subgenera: Cancer (Cancer), Cancer (Glebocarcinus), Cancer (Metacarcinus), and Cancer (Romaleon). These are now treated as separate genera, along with Platepistoma, which Mary J. Rathbun originally described and which was resurrected in 1991. Since then, additional genera have been created for species formerly in Cancer, leaving the genus with only eight extant species.
The earliest confidently assigned fossils of Cancer are those of C. fujinaensis from the Miocene of Japan.
Quick Facts
- Taxon
- Cancer
- Type Species
- Cancer pagurus
- Type Species Authority
- Linnaeus, 1758
Facts from the source article.
Lore & Background
The species placed in the genus Cancer are united by the presence of a single posterolateral spine, anterolateral spines with deep fissures, 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.
When zoological nomenclature was first standardised by Carl Linnaeus in the 1758 10th edition of Systema Naturae, 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's 1802 work. Latreille designated C. pagurus to be the type species in 1817.
In 1975, J. Dale Nations divided the genus Cancer into four subgenera: 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.
Reader's Guide
The genus Cancer holds historical significance as the original Linnaean container for almost all crustaceans, a testament to the early state of zoological classification. Its subsequent restriction to a group of true crabs illustrates the refinement of taxonomic practice over two centuries. The division of the genus into subgenera by J. Dale Nations in 1975, and the later elevation of those subgenera to full genera, reflects ongoing revision based on morphological characters. The current circumscription, with only eight extant species, results from the transfer of many former members to genera such as Glebocarcinus, Metacarcinus, and Romaleon. The genus is thought to have evolved in the northern Pacific Ocean during the Miocene, with the earliest confidently assigned fossils from Japan. Its spread across the Pacific and into the Atlantic by the Pliocene or Pleistocene, crossing the equator and the Straits of Panama, indicates a successful biogeographic expansion. The inclusion of familiar littoral crabs such as the European edible crab, Jonah crab, and red rock crab gives the genus economic and ecological relevance. Uncertainty remains regarding the placement of some fossil species, such as Cancer tomowoi, known only from sternal and leg fragments, highlighting the limitations of dorsal-carapace-based diagnoses.
Did You Know?
- The genus Cancer originally included almost all crustaceans when Carl Linnaeus standardized zoological nomenclature in 1758.
- The type species of the genus is Cancer pagurus, the European edible crab, designated by Pierre André Latreille in 1817.
- The earliest confidently assigned fossils of Cancer are from the Japanese Miocene.
- The genus is thought to have evolved in the northern Pacific Ocean and spread to the Atlantic by crossing the equator and the Straits of Panama.
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