Common Hermit Crab
Facts about this animal
The Common Hermit Crab has a carapace of up to 4.5 cm long and a maximum body length of 8 cm. The colour is reddish or brownish. The carapace which covers the cephalothorax is less hard than it is normal for other groups of decapod crustaceans. The soft abdomen is completely devoid of hard plates and is coiled down asymmetrically to the right. The first pair of walking legs has large forceps, the right one being larger. They have a hard, rough, granular surface like the two following pairs of walking legs while the remaining two pairs of walking legs are strongly reduced likewise most abdominal legs which serve to hold the shell and to circulate breathing water. The thin abdominal skin is the main organ of respiration. The two compound eyes are to be found on movable stalks. The four antennae are short.
To protect its soft body the Common Hermit Crab uses shells of a number of marine snail species, including edible periwinkle (Littorina littorea), flat periwinkle (Littorina obtusata), dog whelk (Nucella lapillus) and - in deeper waters - whelk (Buccinum). If disturbed it retreats deeper into the shell and barricades the shell’s opening with the walking legs, especially with the right forceps. In the warmer parts of its range, the sea anemone Calliactis parasitica is often found growing on the shell occupied by the Common Hermit Crab. In colder waters, this role is filled by Hormathia digitata. Because the Common Hermit Crab is carrying them around they profit from additional food resources. If the Common Hermit Crab moults to grow it swaps its old shell for a larger one and transplants its sea anemones which help to protect him with their nettling tentacles. Frequently Common Hermit Crabs perform hostile takeover of the shell of congeners. A parasitic barnacle (Peltogaster paguri) is sometimes mistaken for the crab's eggs.
The Common Hermit Crab is an omnivorous scavenger but can also filter organic particles from the water or graze on periphyton.
Reproduction takes place in January and February but in deeper waters, where seasons are not very distinct, females can be found carrying eggs throughout the year. Eggs are usually carried for about two months attached to the few abdominal legs. The symmetrical hatchlings will stay for some additional weeks with their mother before becoming pelagic. Maturity is typically reached before one year of age.
Did you know?
that the polychaete worm Nereis fucata may live in the shell occupied by the Common Hermit Crab stealing food from its host which is called commensalism? that another hermit crab, Pagurus pridauxi, uses its symbiotic sea anemone Adamsia palliata as living bin where it stores food to consume later?
|Name (Scientific)||Pagurus bernhardus|
|Name (English)||Common Hermit Crab|
|Name (French)||Pagure, Pagureplus, Bernard-l'ermite|
|Name (German)||Gemeiner Einsiedlerkrebs, Berhardskrebs|
|Name (Spanish)||Ermitano soldado|
|Local names||Danish: Eremitkrebs
Dutch: Gewone heremietkreeft
Italian: Paguro Bernardo
Norwegian: (St.) Bernhardkreps
Portuguese: Paguro, Casa-alugada, Bernardo-o-eremita
|CITES Status||Not listed|
|CMS Status||Not listed|
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|Range||European coasts of Atlantic Ocean from Iceland, Svalbard and Russia to Portugal. It is not present either in the Mediterranean or in most of the Baltic Sea.|
|Habitat||On rocky to sandy but not muddy bottoms or in seagrass meadows from the shore to depths of 140 m.|
|Wild population||Common and widespread|
|Zoo population||70 reported to ISIS (2008)|
In the Zoo
Why do zoos keep this animal
The Common Hermit Crab is kept for educational purposes. It serves to demonstrate the symbiosis between a moving and little protected arthropod and an otherwise sessile, well armed cnidarian. It is hardy and can be shown in touch pools.