crustaceans a mainly aquatic class of creatures, sharing with other arthropods such as insects and arachnids the characteristics of being invertebrates, with jointed limbs, segmented bodies, and an exoskeleton (exterior skeleton) of chitin.

Most crustaceans are edible, although some are not worth eating and some are so small that they have been disregarded as human food; but interest has been growing in krill, the collective term for the minuscule amphipods which abound in polar waters, and very small crustaceans of this sort already enter into the composition of certain SE Asian shrimp pastes. On a larger scale, the best-known examples are the various sorts of lobster, shrimp, prawns, and crabs; but there are others, including the goose-necked barnacle.