Appearance
The carapace of "C. pagurus" adults is a reddish-brown colour, while in young specimens it is purple-brown. It occasionally bears white patches, and is shaped along the front edge into nine rounded lobes, resembling a pie crust. Males typically have a carapace 60 millimetres long, and females 98 mm long, although they may reach up to 150 mm long in exceptional cases. Carapace width is typically 150 mm, or exceptionally up to 250 mm. A fold of the carapace extends ventrally to constitute a branchial chamber where the gills lie.The first pereiopod is modified into a strong cheliped : the claw's fingers, the dactylus and propodus, are black at the tips. The other pereiopods are covered with rows of short stiff setae; the dactylus of each is black towards the tip, and ends in a sharp point.
From the front, the antennae and antennules are visible. Beside these there are the orbits in which the eyes are situated. The mouthparts comprise three pairs of maxillipeds, behind which there are a pair of maxillae, a pair of maxillules, and finally the mandibles.
In common with most crabs, the abdomen is folded under the thorax and shows clear sexual dimorphism: in males it is comparatively narrow, whereas in the female it is wider.
Distribution
"Cancer pagurus" is abundant throughout the northeast Atlantic as far as Norway in the north and northern Africa in the south, on mixed coarse grounds, mud and sand from the shallow sublittoral to depths of about 100 metres. It is frequently found inhabiting cracks and holes in rocks but occasionally also in open areas. Smaller specimens may be found under rocks in the littoral zone. Unconfirmed reports suggest that "C. pagurus" may also occur in the Mediterranean Sea and Black Sea.Adult "C. pagurus" are nocturnal, hiding buried in the substrate during the day, but foraging at night up to 50 metres from their hideouts. Their diet includes a variety of crustaceans and molluscs. It may stalk or ambush motile prey, and may dig large pits to reach buried molluscs. The main predator of "Cancer pagurus" is the octopus, which will even attack them inside the crab pots that fishermen use to trap them.
Compared to other commercially important crab species, relatively little is known about diseases of "Cancer pagurus". Its parasites include viruses, such as the white spot syndrome virus, various bacteria that cause dark lesions on the exoskeleton, and "Hematodinium"-like dinoflagellates that cause "pink crab disease". Other microscopic pathogens include fungi, microsporidians, paramyxeans and ciliates. "Cancer pagurus" is also targeted by metazoan parasites, including trematodes and parasitic barnacles. A number of sessile animals occasionally settle as epibionts on the exoskeleton of "C. pagurus", including barnacles, sea anemones, serpulid polychaetes such as "Janua pagenstecheri", bryozoans and saddle oysters.
Behavior
Reproduction occurs in winter; the male stands over the female and forms a cage with his legs protecting her while she moults. Internal fertilisation takes place before the hardening of the new carapace, with the aid of two abdominal appendages. After mating, the female retreats to a pit on the sea floor to lay her eggs. Between 250,000 and 3,000,000 fertilised eggs are held under the female's abdomen for up to eight months until they hatch.The first developmental stage after hatching is a planktonic larva called the zoea that develops into a postlarva, and finally a juvenile. The first juvenile stage is characterised by a well-developed abdomen, which will, in time, become reduced in size and folded under the sternum. Juveniles settle to the sea floor in the intertidal zone, where they stay until they reach a carapace width of 60–70 mm and then migrate to deeper water. The growth rate in males slows from an increase in carapace width of 10 mm per year before it is eight years old, to 2 mm per year thereafter. Females grow at about half the rate of males, probably due to the energetic demands of egg laying. Sexual maturity is reached at a carapace width of 12.7 cm in females, and 11 cm in males. Longevity is typically 25–30 years, although exceptional individuals may live for up to 100 years.
Habitat
"Cancer pagurus" is abundant throughout the northeast Atlantic as far as Norway in the north and northern Africa in the south, on mixed coarse grounds, mud and sand from the shallow sublittoral to depths of about 100 metres. It is frequently found inhabiting cracks and holes in rocks but occasionally also in open areas. Smaller specimens may be found under rocks in the littoral zone. Unconfirmed reports suggest that "C. pagurus" may also occur in the Mediterranean Sea and Black Sea.Adult "C. pagurus" are nocturnal, hiding buried in the substrate during the day, but foraging at night up to 50 metres from their hideouts. Their diet includes a variety of crustaceans and molluscs. It may stalk or ambush motile prey, and may dig large pits to reach buried molluscs. The main predator of "Cancer pagurus" is the octopus, which will even attack them inside the crab pots that fishermen use to trap them.
Compared to other commercially important crab species, relatively little is known about diseases of "Cancer pagurus". Its parasites include viruses, such as the white spot syndrome virus, various bacteria that cause dark lesions on the exoskeleton, and "Hematodinium"-like dinoflagellates that cause "pink crab disease". Other microscopic pathogens include fungi, microsporidians, paramyxeans and ciliates. "Cancer pagurus" is also targeted by metazoan parasites, including trematodes and parasitic barnacles. A number of sessile animals occasionally settle as epibionts on the exoskeleton of "C. pagurus", including barnacles, sea anemones, serpulid polychaetes such as "Janua pagenstecheri", bryozoans and saddle oysters.
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