About the systematics of Palaearctic Eurytemora (Copepoda, Calanoida) based on morphological analysis, with focus on Eurytemora gracilicauda Akatova, 1949

Abstract

We studied the morphology of Eurytemora from inland waters at the shores of the White and Pechora seas and from the Lena River delta, and revealed a ubiquitous presence of Eurytemora gracilicauda Akatova, which results we confirmed with genetic data. We found this species for the first time in the Pechora Sea basin. In the White Sea basin, this species was previously described as E. brodskyi Kos, with the name that we suggest is a junior synonym of E. gracilicauda. E. gracilicauda differs from the co-living species: E. lacustris (Poppe), E. arctica Wilson M. S. & Tash, and E. raboti Richard, by the structure and armament of the caudal rami and the fifth legs (P5) of males and females. The caudal rami of both males and females were elongated. The female caudal rami showed a surface covered by spines. The male caudal rami were bare, or with rare spines on the sides. The appendages of the female P5 were also elongated: the length of the inner spine on the distal exopod segment was 2.27 ± 0.12 times as long as the outer spine; the exopod of the male right P5 had a specific trigonal ledge with a short spinule, and the coxopods (both or at least one) had groups of spinules. The morphometric parameters of the females were quite stable, while those of the male showed high variability within and between populations (CV = 11.5-43.5%). Similarities and differences of E. gracilicauda and three allochoric Eurytemora species were analysed, and the results presented herein.