Select another group Birds Bryozoans Crustaceans Fish Jellies Mammals Molluscs Plants Reptiles Segmented Worms Sponges Starfish & urchins Select a crustacean Acorn barnacle Antarctic krill Atlantic lobster Californian spiny lobster Christmas Island crab Common shore crab Cystisoma/    Giant amphipod Gnathophausia/    Red mysid shrimp Harlequin shrimp Hermit crabs Kelp curler Krill Lobster Mantis shrimpOplophorus Porcelain crab Red rock crab Sand bubbler crab Sand hopper Shrimp Southern kelp crab Sponge shrimp Velvet swimming crab Vent shrimps Xanthid crab

Crustaceans

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea

There are approximately 39,000 species of crustacean including crabs, lobsters, shrimps, barnacles and woodlice. Most are aquatic and of these, most are marine.

Like all arthropods, crustaceans have a hard external skeleton (exoskeleton). They have two pairs of antennae, a pair of mandibles, two pairs of maxillae (mouth parts used for eating) on their heads, a pair of appendages on each body segment (head, thorax, and abdomen) and a pair of compound eyes (usually on stalks).

Crustaceans vary in size from the massive Japanese spider crab, which has a leg span of 3.7m (12ft), to the tiny water fleas, which are only about 0.25mm (0.009in) long.

Some species are active predators, some are filter-feeders and others are scavengers. They may be free-living, sessile or even parasitic. Woodlice are the most terrestrial of the crustaceans. Although they tend to live in damp places, some species can survive in deserts. A number of crab species are semi-amphibious, returning to water only to breed.

Although most crustaceans have separate sexes, barnacles have both male and female parts (hermaphrodite). Crustaceans lay eggs and some species have a larval stage called a nauplius.