The Common Marine Hermit Crab (Pagurus bernhardus) is a saltwater aquatic decapod (10-armed) crustacean. It is also known as the Soldier Crab.
Hermit crabs include the Marine Hermit Crab, which lives in saltwater, and the Land Hermit Crab, which is terrestrial in tropical regions.
The Common Marine Hermit Crab is a crab inside a shell – its mobile home. It finds empty mollusc shells to live in. It has a long soft body – not like land crabs which have a hard exo-skeleton – which is why it looks for a hard shell to protect it. It can put its whole body inside the shell. As it grows, it looks for larger shells.
The Common Marine Hermit Crab has a spirally-curved soft body (abdomen) with a columella on the tip, which is used to hold onto the shell it occupies. It has 10 appendages (legs, called pereiopods), but two of them are claws, called nippers, pinchers, or chelipeds. Its large black compound eyes are at the end of an eyestalk. It has gills to breathe (like fish).
The Marine Hermit Crab ranges is size and shape. The Common Marine Hermit Crab measures 3-4 centimetres (1-1.5 inches) long.
It is common in Europe’s Atlantic Ocean coasts, from Iceland and Russia to southern Portugal. It is not found in the Mediterranean Sea.
The Marine Hermit Crab spends most of its life underwater. It is aquatic. It prefers saltwater and can live in shallow reefs or deep oceans. It is a bottom-dweller, living on the sea bed. It prefers ocean beds with rocky and sandy terrains.
It competes with other Hermit Crabs for a shell to live in. It inspects the shell first, for size, to see if it will fit inside. If a seashell is not available, it will live in a tin can or any other protective object on the bottom of the ocean.
The Marine Hermit Crab is related to squat lobsters and porcelain crabs, and is not a true crab. It is not related to the snail.
It is an omnivorous detritivore, eating small aquatic animals, such as plankton, and carrion (the meat of dead animals, such as fish). It does not have any teeth. It pinches its food with its nippers.
It is nocturnal, active mainly at night.
The life cycle of the Marine Hermit Crab is: (1) Nauplius (inside the egg), (2) Protozoea (inside the egg), (3) Zoea (after the eggs hatch – this is the larvae stage and as it grows, it moults (sheds its skin), and (4) Megalopa (adult crab).
It has a lifespan of about 20 years.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM