CLAWS

Crustaceans are jointed-legged animals. Their bodies are covered with hard, but relatively flexible, exoskeletons.

Crabs, lobsters, shrimps and prawns are all crustaceans.

There are more than 42,000 different species of crustaceans worldwide. Most of them are marine-based creatures and they live in a variety of habitats; from beach rockpools to the deepest regions of every ocean.

As their shells are hard, crustaceans have to moult (shed) their armoured plating in order to continue growing. Baby lobsters will moult up to seven times before they reach their first birthday.

As they grow older they moult less frequently - which is why very old crustaceans can be identified by the large number of barnacles and other marine life found on their shells.

Lobsters and crabs grow to great ages - some specimens are believed to be more than 70 years old!

Although the hard outer shells of most crustaceans act as highly effective armour protecting them from attack, they do have disadvantages - the main one being a lack of mobility.

That is why most crabs have to move sideways because they lack rotational joints.

The largest known crustacean is the giant Japanese spider crab which can weigh more than 13kgs and has a leg span of over four metres!

Fishermen who have tried to land these monsters have had chunks of flesh torn from their bodies by the crab's giant pincers.

Another giant of the deep is the Alaskan King crab whose thorny claws are used to crush tough clam shells as if they were eggs.

Average individuals weigh in at 5kgs but many animals have been recorded at twice that weight and with two-metre claw spans.

Alaskan King crabs travel along the seafloor in huge numbers in search of food. These groups, which can number many thousands of animals, may walk anything up to 100 miles in a single year.

Among the smallest species is the pea crab, which is smaller than a postage stamp.