Clarification of the taxonomic status of Notodiaptomus anisitsi (Daday, 1905) and related species, with description of a new species from Argentina (Crustacea: Copepoda: Diaptomidae)

The diaptomids discussed represent a group of incompletely known and, at first glance, closely related species. The most conspicuous feature shared among them is the general aspect of the exopodite segment 2 of the male leg 5. Through a study of literature and comparison of descriptions with material from several localities, some of them type localities, of northern Argentina, Uruguay and Paraguay, N. anisitsi Daday, 1905 and N. spinuliferus Dussart, 1985 are redescribed and one new species is described. The validity or possible conspecificity of N. inflexus (Brian, 1925), N. bidigitatus Brehm 1958, and N. perelegans (Wright, 1927) is discussed. Additionally, the variability and the value as diagnostic character of several morphological features, mainly, ornamentation of distal segment of prosome, setation of antennules, basipodite and exopodite of right leg 5 of male, and shape of outer caudal seta are analysed.