Redescription of two species of Microcyclops (Copepoda, Cyclopoida) and use of ordination models to classify American species

Two species of the freshwater copepod genus Microcyclops are redescribed, M. finitimus Dussart, 1984, and M. minor Dussart, 1984 from type specimens. Redescription includes the microstructure of intercoxal sclerites and the basipodites of thoracic appendages, as well as the urosomal microstructure. According to the cluster (UPGMA and Euclidean distance) and PCA analyses performed, it was possible to improve the resolution between the American Microcyclops species by considering characters such as the distal region of antennal basis, the maxillary ornamentation, and the thoracic appendages, especially the intercoxal sclerites and medial margin of the basipodite of the first to fourth trunk limbs. Considering a set of 28 morphological characters in adult females, traditional features such as the length ratio of caudal rami, the length: width ratio of the third endopod of the fourth leg, or the length ratios between apical setae of the same segment, appear to be less important for defining differences between very similar species of American Microcyclops. In these analyses, the redescription of the Palearctic M. varicans was considered, and this species was clearly separated from the American M. dubitabilis Kiefer, 1934 and M. inarmatus Gutierrez-Aguirre and Cervantes-Martinez, 2016.

Automated summary

Two species of the freshwater copepod genus Microcyclops, M. finitimus and M. minor, were redescribed based on type specimens. The redescription included the microstructure of various body parts. Cluster and PCA analyses were used to improve the resolution between American Microcyclops species. Morphological characters such as the distal region of antennal basis, maxillary ornamentation, and thoracic appendages were found to be important for differentiating species.