Classes and subclasses
- Thylacocephala? †
- Malacostraca (includes Decapods)
Crustaceans (Crustacea) form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. Like other arthropods, crustaceans have an exoskeleton, which they moult to grow.
Size ranges of crustaceans
The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm , to the Japanese spider crab with a leg span of up to 3.8 m and a mass of 20 kg.
How they are different from other arthropods
They are distinguished from other groups of arthropods, such as insects, myriapods and chelicerates, by the possession of biramous (two-parted) limbs, and by the nauplius (that use appendages of the head the antennae for swimming) form of the larvae.
Most crustaceans are free-living aquatic animals, but some are terrestrial (e.g. woodlice), some are parasitic (e.g. Rhizocephala, fish lice, tongue worms) and some are sessile (don’t move much) (e.g. barnacles).
The group has an extensive fossil record, reaching back to the Cambrian, and includes living fossils such as Triops cancriformis, which has existed apparently unchanged since the Triassic period.
Crustaceans as part of the food chain
More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimp and prawns. Krill and copepods are not as widely fished, but may be the animals with the greatest biomass on the planet, and form a vital part of the food chain.
Who studies crustaceans
The scientific study of crustaceans is known as carcinology (alternatively, malacostracology, crustaceology or crustalogy), and a scientist who works in carcinology is a carcinologist.
source adapted from: http://en.wikipedia.org/w/index.php?title=Crustacean&oldid=609551515