Redescription and taxonomic validity of Leptodiaptomus cuauhtemoci (Osorio- Tafall, 1941) (Copepoda, Calanoida), with notes on its known distribution

Within the American freshwater calanoid copepods, Leptodiaptomus includes species whose taxonomical status is still unclear. One of them is L. cuauhtemoci (Osorio-Tafall), for decades considered to be a synonym of L. siciloides (Lilljeborg); another species involved in this problem is L. assiniboiensis (Anderson & Fabris) described from Canada, which had been found to be closely related to L. cuauhtemoci. This species remained of uncertain taxonomy because the type material was lost decades ago. In order to disentangle this controversy, type specimens of L. assiniboiensis, topotypic specimens of L. cuauhtemoci from a National Park in central Mexico, and confirmed specimens of L. siciloides from different locations in Mexico and the United States were used to define the status of these species. Leptodiaptomus cuauhtemoci was fully redescribed using SEM. Based on the main characters used to differentiate species of Diaptomidae, L. assiniboiensis (= Diaptomus intermedius Anderson & Fabris) turned out to be conspecific and a junior synonym of L. cuauhtemoci, which then becomes the valid name. The latter species shows taxonomically relevant differences with respect to L. siciloides. In the females the main differences is that the lateral spiniform processes on the genital somite are broader-based in L. cuauhtemoci, the genital field is different in both species. In L. cuauhtemoci the fifth leg endopods bear two large, broad, subterminal setae of about the same size, differently built than in L. siciloides. The male L. cuauhtemoci is slenderer, with wings of pediger 5 clearly more developed than those of L. siciloides. The armature of the modified right antennules and the structure of the fifth leg differ in both species. A large coxal spine is present on the right fifth leg of L. siciloides, whereas it is absent in L. cuauhtemoci. These differences were considered to be enough evidence for recognizing L. cuauhtemoci as a separate, valid species. Topotypic specimens of L. cuauhtemoci are designated as neotypes.