Crustaceashrimps, crabs, lobsters, water fleas, and relatives

Ap­prox­i­mately 30,000 species make up this Sub­phy­lum. Most are aquatic; of these, the ma­jor­ity are ma­rine but some are found in fresh water. Mem­bers of the Sub­phy­lum in­clude lob­sters, crabs, cray­fish, shrimp, cope­pods, bar­na­cles, and sev­eral other groups of or­gan­isms. All have two pairs of an­ten­nae, a pair of mandibles, a pair of com­pound eyes (usu­ally on stalks), and two pair of max­il­lae on their heads, fol­lowed by a pair of ap­pendages on each body seg­ment (crus­tacean bod­ies usu­ally are made up of head, tho­rax, and ab­domen, al­though the seg­ments com­pos­ing these tag­mata dif­fer among dif­fer­ent Classes). The ap­pendages are prim­i­tively branched (bi­ra­mous), and al­though this con­di­tion is mod­i­fied in many species, adults al­ways have at least some bi­ra­mous ap­pendages. Crus­taceans respire via gills. Like other arthro­pods, all have a hard but flex­i­ble ex­oskele­ton.

Most crus­taceans are free-liv­ing, but some are ses­sile and a few are even par­a­sitic. Most use their max­il­lae and mandibles to take in food. The walk­ing legs, in­clud­ing spe­cial­ized che­lipeds, may be used to help cap­ture prey. Some crus­taceans fil­ter tiny plank­ton or even bac­te­ria from the water; oth­ers are ac­tive preda­tors; while still oth­ers scav­enge nu­tri­ents from de­tri­tus.

Most crus­taceans are dioe­cious. The ac­tual mech­a­nisms by which fer­til­iza­tion is achieved vary greatly. Some crus­taceans hatch young that are like minia­ture adults; oth­ers go through a lar­val stage called a nau­plius.

Many species, in­clud­ing lob­sters, cray­fish, bar­na­cles, and crabs are im­por­tant to human economies, some very much so. Oth­ers, such as krill, are at the base of ex­tremely im­por­tant ma­rine food chains. Still oth­ers are cru­cial in re­cy­cling nu­tri­ents trapped in the bod­ies of dead or­gan­isms.


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Source:

Hick­man, C.P. and L. S. Roberts. 1994. An­i­mal Di­ver­sity. Wm. C. Brown, Dubuque, IA.

Br­usca, R. C., and G. J. Br­usca. In­ver­te­brates. 1990. Sin­auer As­so­ci­ates, Sun­der­land, MA.

Pearse, V., J. Pearse, M. Buchs­baum, and R. Buchs­baum. 1987. Liv­ing In­ver­te­brates. Black­well Sci­en­tific Pub­li­ca­tions, Palo Alto, Ca.

Con­trib­u­tors

Phil Myers (au­thor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.