The members of the Euphausiacea are commonly calledkrill and are all marine shrimp-like species whosepleopods (abdominal appendages) function as swimmerets. They swarm and mostly feed onplankton. This group is composed of only 90 species, some of which are the most abundant species on the planet; in fact, it is estimated that the biomass of theAntarctic krillEuphausia superba' is 500 million tons.[4]
Decapoda is a group with 15,000 species[5] which have 5 pairs of thoracopods and a well-developed carapace that covers thegills (which are exposed in krill). They includelobsters,crabs,shrimp andprawns. The decapods are further subdivided on the basis of the gill structure into two subordersDendrobranchiata (prawns) andPleocyemata, which is further subdivided into several infraorders, such as theCaridea (true shrimp), theStenopodidea (boxer shrimp) and theAnomura and the Brachyura (crabs) and so forth.[6][7]
Lastly, there is an extinct order that contains only one family,Angustidontidae, which in turn contains two genera,Angustidontus andSchramidontus.[8] They were originally consideredeurypterids, but later their possible relationship with decapods was established.[8][9]
Thephylogeny of the Malacostraca is debated.[6] In particular, themonophyly of Eucarida is also under question:
Monophyletic: many argue that the Eucarida group is aclade, sister to the Peracarida clade[6][10] or to the basal Malacostraca.[7][11] or to Mysida (paraphyletic Schizopoda)[12]
Paraphyletic: some have proposed a paraphyletic Eucarida forming a clade with a nested Peracarida.[13]
Polyphyletic: some have grouped Euphausiacea with Mysida to form theSchizopoda,[14][15] or the Euphausiacea with the Hoplocarida,[16] with Decapoda basal to the Peracarida.[15][16]
^R. Siewing (1963). "Studies in malacostracan morphology: results and problems". In H. B. Whittington; W. D. Rolfe (eds.).Phylogeny and Evolution of Crustacea.Cambridge, Massachusetts:Museum of Comparative Zoology. pp. 85–103.
^L. Watling (1999). "Towards understanding the relationship of the peracaridan orders: the necessity of determining exact homologies". In Frederick R. Schram; J. Carel von Vaupel Klein (eds.).Crustaceans and the Biodiversity Crisis. Proceedings of the Fourth International Crustacean Congress, Amsterdam: The Netherlands, July 20–24, 1998, Vol. I.Brill Publishers. pp. 73–89.ISBN978-90-04-11387-9.
^Georg Ossian Sars (1870).Carcinologiske Bidrag til Norges Fauna over de ved Norges Kysters forekommende Mysider. Vol. 1.Christiana: Brøgger & Christies Bogtrykkeri.
