A reevaluation of the North and Central American Arctodiaptomus dorsalis (Marsh, 1907) (Calanoida, Diaptomidae), with reallocation to the genus Mastigodiaptomus and description of a new species

The freshwater genus Arctodiaptomus Kiefer, 1932 is a Palaearctic genus, and comprises nearly 75 nominal species. Arctodiaptomus dorsalis (Marsh, 1907), a diaptomid species originally described within the genus Diaptomus, has long been reported throughout the Americas. Its morphology diverges from the generic diagnostic features; thus, its taxonomic position has been doubtful. Furthermore, its phenotypic variability has resulted in local synonymies and suggested it as a species complex. In this study, we reassign the taxonomic position of “A. dorsalis” based on the examination of type and non-type material from North and Central America, the analyses of mitochondrial COI, and biogeographic affinities. Our results show that the American populations attributed to “A. dorsalis” in the study area diverge genetically from the genus Arctodiaptomus by 27–29%, and share key diagnostic features with Mastigodiaptomus Light, 1939, therefore, this species should be transferred to that genus. Furthermore, the synonymized species Diaptomus alter Herbst, 1960 (Nicaragua), and D. dampfi Brehm, 1932 (Guatemala) were examined from type locality material and found to share the diagnostic characters of “A.” dorsalis. In addition, we describe Mastigodiaptomus cucapa sp. nov. linked before to “A”. dorsalis, thus contributing to disentangle this taxonomic problem.