ARTHROPODA Subphylum Hexapoda Protura, Springtails, Diplura, and Insects
NINE Phylum ARTHROPODA SUBPHYLUM HEXAPODA Protura, springtails, Diplura, and insects ROD P. MACFARLANE, PETER A. MADDISON, IAN G. ANDREW, JOCELYN A. BERRY, PETER M. JOHNS, ROBERT J. B. HOARE, MARIE-CLAUDE LARIVIÈRE, PENELOPE GREENSLADE, ROSA C. HENDERSON, COURTenaY N. SMITHERS, RicarDO L. PALMA, JOHN B. WARD, ROBERT L. C. PILGRIM, DaVID R. TOWNS, IAN McLELLAN, DAVID A. J. TEULON, TERRY R. HITCHINGS, VICTOR F. EASTOP, NICHOLAS A. MARTIN, MURRAY J. FLETCHER, MARLON A. W. STUFKENS, PAMELA J. DALE, Daniel BURCKHARDT, THOMAS R. BUCKLEY, STEVEN A. TREWICK defining feature of the Hexapoda, as the name suggests, is six legs. Also, the body comprises a head, thorax, and abdomen. The number A of abdominal segments varies, however; there are only six in the Collembola (springtails), 9–12 in the Protura, and 10 in the Diplura, whereas in all other hexapods there are strictly 11. Insects are now regarded as comprising only those hexapods with 11 abdominal segments. Whereas crustaceans are the dominant group of arthropods in the sea, hexapods prevail on land, in numbers and biomass. Altogether, the Hexapoda constitutes the most diverse group of animals – the estimated number of described species worldwide is just over 900,000, with the beetles (order Coleoptera) comprising more than a third of these. Today, the Hexapoda is considered to contain four classes – the Insecta, and the Protura, Collembola, and Diplura. The latter three classes were formerly allied with the insect orders Archaeognatha (jumping bristletails) and Thysanura (silverfish) as the insect subclass Apterygota (‘wingless’). The Apterygota is now regarded as an artificial assemblage (Bitsch & Bitsch 2000).
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