Phylum Arthropoda Subphylum Crustacea: shrimps, crabs, lobsters, barnacles, slaters, and kin

No group of plants or animals on the planet exhibits the range of morphological diversity seen among the extant Crustacea.' This provocative quote from Martin and Davis (2001) highlights at least one attribute of the group. Nevertheless, the body plan of the Crustacea has a number of unifying characteristics, including a five-segmented head with two pairs of antennae and an elongate body that may be ctivided into two more-orless distinct sections - generally the thorax or/body' and the pleon or' abdomen'. Each of these sections bears multisegmented appendages (mostly limbs) that are primitively biramous (forked) but some are uniramous in many groups. Brusca and Brusca (2002) gave a succinct summary of the characteristics of the subphylum. In addition to enormous diversity of form, crustaceans exhibit a great range of sizes (exceeded only by molluscs, which can claim the largest individual invertebrate in the form of the colossal squid), from minute interstitial and parasiticforms (e.g.Tantulocarida) measuring as little asa tenth ofa millimetre to giant crabs, lobsters, and isopods with a body size of up to half a metre in length or breadth and weighing up to 20 kilograms. By virtue of their edibility, many crustaceans are prized items on restaurant menus around the world.