Cancer (genus)

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Cancer
Pocket crab (Cancer pagurus)

Pocket crab ( Cancer pagurus )

Systematics
Order : Decapods (decapoda)
Subordination : Pleocyemata
Partial order : Crab (Brachyura)
Superfamily : Cancroidea
Family : Crabs (Cancridae)
Genre : Cancer
Scientific name
Cancer
Linnaeus , 1758

Cancer is a crab species from the family of crabs (Cancridae). The species of this genus are common in the Pacific and Atlantic. The famous crab ( Cancer pagurus ) from the North Seaalso belongs to it.

features

The carapace of these crabs is approximately egg-shaped, with the length being 58% to 66% of the width. On the front edge there are five small points between the eye sockets. The distance between the eyes is 22% to 29% of the carapace width. At the front edge of the carapace there are nine, more square teeth, which are separated from each other by clear gaps. These teeth are usually blunt, but they can also be elongated as small teeth. The rear side edge is more or less concave and provided with a thorn. The rear edge of the carapace is convex. The ornamentation of the carapace is indistinct to distinct, the surface can be smooth or granular with tubercles . The scissors can also have a smooth or granular surface. They are rather short and have three to four ridges. The scissor fingers have large blunt teeth on their insides.

distribution

Types of cancer are native to the eastern Pacific littoral on the coasts of North and South America and the northern Atlantic. The oldest fossil find is Cancer fujinaensis from Japan and dates from the Miocene . One therefore locates the genus Cancer in the North Pacific during the Miocene. The species then spread across the Northeast Pacific, both across the Equator into the Southeast Pacific and through the Panama Strait into the Atlantic.

Systematics

species

The types of Cancer differ from other edible crabs in the ornamentation and shape of the carapace . In addition to the morphology of the scissors, the intragenerically carapace, especially the shape of the teeth on the front edge, is the most important distinguishing feature. The genus Cancer includes the following eight recent species and three known as fossils:

Research history

Carl von Linné used the term “Cancer” ( ancient Greek καρκίνος karkinos “cancer”) in the 10th edition of the Systema Naturae to summarize all the crab-like crustaceans known at the time. The taxon cancer was thus originally to be understood as a synonym for Crustacea . As knowledge about the diversity of crustaceans and crabs grew, the definition of cancer needed to be adjusted . As early as 1802, Pierre André Latreille restricted the taxon to its current importance as a crab genus. In 1810 he identified the crab as a type species . Even after Latreille's definition, various types of cancer were counted as Cancer , which is why constant adjustments were required. J. Dale Nations divided the genus into four sub-genera in 1975, which in turn were considered by Carrie E. Schweitzer and Rodney M. Feldmann in 2000 as separate genera next to Cancer : Glebocarcinus , Metacarcinus and Romaleon . The genus, which once comprised more than 30 species, is thus limited to eight known species. The classification of cancer and the edible crab family is still under discussion, since molecular genetic studies tend not to support the current system.

Individual evidence

  1. a b c Carrie E. Schweitzer, Rodney M. Feldmann: Re-evaluation of the Cancridae Latreille, 1802 (Decapoda: Brachyura) including three new genera and three new species . In: Contributions to Zoology . tape 69 , no. 4 , 2000, pp. 223–250 ( decapoda.nhm.org [PDF; 3.2 MB ; accessed on February 17, 2013]).
  2. a b c Frederick R. Schram, Peter KL Ng: What is Cancer? In: Journal of Crustacean Biology . tape 32 , no. 4 , 2012, p. 665-672 , doi : 10.1163 / 193724012X640650 .
  3. PKL Ng, D. Guinot, PJF Davie: Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world . In: Raffles Bulletin of Zoology . tape 17 , 2008, p. 1–286 ( rmbr.nus.edu.sg [PDF; 8.0 MB ; accessed on February 17, 2013]).
  4. ^ JD Nations: The genus Cancer (Crustacea: Bachyura): systematics, biogeography, and fossil record . In: Natural History Museum of Los Angeles County Science Bulletin . tape 23 , 1975, p. 1–104 ( nhm.org [PDF; 10.0 MB ; accessed on February 17, 2013]).

Web links

Commons : Cancer  - Collection of Images