All crustaceans have a double set of antennas. Like all arthropods they have an external skeleton. The body is often elongated and segmented and there is usually one pair of legs attached to each segment. The more advanced species tend to have fewer and more specialized legs. Sexes are usually separate, but exceptions exist. Many species of shrimps are born males and convert to females after a few years.
Most crustaceans are aquatic, but there are terrestrial species too.
All crustaceans represented on seawater.no are members of one of the following classes.