CREATURE FEATURE - CRUSTACEANS
Also known as the 'insects of the sea', this diverse group includes animals with widely differing lifestyles, from parasites to filter feeders, plankton dwellers to beach hoppers.
Crustaceans are specialised for life in water and have gills for oxygen uptake. All possess an external skeleton made from tough chitin. This is like a suit of armour and provides protection and a place for muscles to attach to. It allows for great flexibility, combined with numerous paired limbs which are specialised for feeding, crawling and swimming. However, the exoskeleton restricts growth and all crustaceans must moult, or shed their exoskeleton, in order to grow.
All crustaceans also share a complicated life cycle, often involving several different larval stages. The number of these larval stages differ among species but most include a planktonic stage which look nothing like the adult.
Some crustaceans stay in the plankton throughout their lives - tiny shrimp-like krill are an important food source to the largest of animals, the blue whale. Other species' larvae develop into more familiar forms. Barnacle larvae settle out of the plankton and cement their heads to rock, develop hard plates to protect their bodies then wave their 'legs' in the water and kick food into their mouths!
Other crustaceans include crabs. They have 10 walking legs, a hard carapace (covering the main body) and pincers which are used for picking up food or for self defence. If attacked, crabs and other crustaceans can escape danger by deliberately shedding an injured or trapped limb - they can grow a new one when they next molt. Lobsters may grow to over 1m long, weigh over 6kg and live for over 60 years!