A new species of Notodiaptomus Kiefer, 1936 (Copepoda, Diaptomidae) from the Amazon and Orinoco River Basins

A new species of Notodiaptomus, Notodiaptomus simillimus sp. nov., based on the female originally but erroneously assigned to Rhacodiaptomus calatus, and the corresponding newly discovered male, is described and illustrated in detail. The designation of the female as a new species of Notodiaptomus, and the recognition of the corresponding new male, is based on detailed morphological and biometrical studies, analysis of the known distribution and material from laboratory cultures. Morphological analysis demonstrated that the female shares the form of the external genital area and setal armature of the exopod 2 of leg 5 with other species of Notodiaptomus but they differ from those exhibited by species of Rhacodiaptomus. The distributions of the female and male assigned to Notodiaptomus simillimus sp. nov. overlap and include the Atabapo and Guaviare Rivers and Lago Calado. On the other hand, the distributions of the males and females originally assigned to R. calatus are disjunct and where they overlap, that is, in Lago Calado, each is accompanied by its respective mate. Laboratory cultures showed that, as expected, copulation did not occur between males and females described originally as R. calatus. This experiment demonstrated the existence of reproductive isolating mechanisms between these females and males, and confirmed the existence of two distinct genetic pools, i.e. two different species, the original males being of the valid R. calatus and the female a new Notodiaptomus. This female and the corresponding newly discovered male are N. simillimus. The new species is closely related to N. coniferoides.