Common Hermit Crab (Pagurus bernhardus)
While there are many species of hermit crab around the UK by far the most common is P. bernhardus, the common hermit crab. It is common around the UK, Iceland, the Faroe Islands and Scandinavia, but its range does not extend into the warmer waters of the Mediterrenean. Unlike all other crab species the common peeler crab does not have its own carapace and must find the discarded shell of another sea creature and make this its home. The hermit crab will then move itself around with the shell on its back and retreat into the shell when it is threatened by a predator. As the hermit crab grows it must leave its original shell and search for a larger and more suitable home. Hermit crab sometimes form a symbiotic relationship with a white ragworm. The worm will also live in the shell with the crab and eat any excess food matter that gets into the shell. Hermit crabs will crawl along the seabed and will eat any decomposing plant or animal matter that they come across. They also have the ability to filter feed and consume plankton and other forms of microscopic sea creatures. Generally, the smaller hermit crabs of a centimetre or so in length will be found around the intertidal zone. When hermit crabs are fully grown as three or four centimetres long they will move into deeper water and be found at depths down to two hundred metres. Common hermit crabs have some use as a bait for sea anglers. More information can be found here.
European Spider Crab (Maja squinado)
A species of crab that is found in the English Channel and along the west coast of England, Scotland and Ireland. The European Spider Crab is unlikely to be confused with any other species of crab in British waters. It has a circular body, usually light orange in colour and covered in bumps and has small spines running along the edge. The body can be 20cm across. Its legs are usually a darker orange and are very long and have two joints in them. The claws are relatively small and are on the end of very long arms that also have two joints in them. The European Spider Crab feeds on plant matter, shellfish and will also eat animals such as starfish, brittle stars and marine worms. They also undertake some form of migration where they move in great numbers (presumably as a defence against predators) into deeper water. This migration is poorly understood but may be linked to breeding. There is a limited fishery for this species of crab, mostly concentrated around ports in the south-west of England. Although there is no demand for this species of crab from UK consumers it is widely eaten in Spain, France and other parts of Europe, and almost all British catches of this species are exported.
Bristly Crab (Pilumnus hirtellus)
Also known as the hairy crab, this species of crab is very small, being just 2-3cm across when fully grown. This species of crab is mostly found around the south and west of the British Isles, and generally stays within the intertidal zone. The body and legs of the bristly crab are reddish-brown in colour and are covered in bristly hair-like structures which give this crab its name. Like all crabs it has eight legs and two claws, with one claw (usually the right) being larger than the other. Its diet is primarily made up of dead and rotting marine creatures.
Masked Crab (Corystes cassivelaunus)
The masked crab is a species of crab which is present mostly around the south and west of the British Isles, although smaller isolated populations are present elsewhere across the country and is also found throughout European waters. It is a small species of crab with a carapace measuring a few centimetres across. It lives on sandy and muddy seabeds and buries itself into the sediment with its long antenna poking out. They generally live just outside the intertidal zone and down to depths of around one hundred metres. It feeds on marine worms and any other small creatures which are found in the sand and sediment where this crab is present.