Studies on the genus Onisimus Boeck, 1871 (Crustacea, Amphipoda, Lysianassoidea, Uristidae)Part I. The brevicaudatus and sextonae species groups

The genus Onisimus Boeck is divided into five species groups to be treated in this and forthcoming publications; a key to these groups includes the genera Menigrates Boeck and Paralibrotus Stephensen. Further keys and redescriptions are presented to all species within two Onisimus species groups. The O. brevicaudatus-group comprises the species O. affinis Hansen, 1886 (= O. dubius Schellenberg, 1935, syn. n.), O. botkini Birula, 1897, O. brevicaudatus Hansen, 1887, O. caricus Hansen, 1887, and O. derjugini Gurjanova, 1929. The O. sextonae-group consists of the species O. abyssi Oldevig, 1959, O. leucopis (G.O. Sars, 1879), and O. sextonae Chevreux, 1926. The full redescriptions of these species are provided in an accompanying Organisms Diversity and Evolution Electronic Supplement. See also Electronic Supplement at: http://www.senckenberg.de/odes/05-07.htm