Ceriodaphnia smirnovi (Crustacea: Cladocera), a new species from the Mediterranean Region, and a phylogenetic analysis of the commonest species.

Species of the genus Ceriodaphnia Dana, 1853 (Crustacea: Cladocera: Daphniidae) are present in the plankton of many freshwater bodies all around the World. However, the taxonomy of the genus is still poorly developed. Most species have been described in the nineteenth century and data on their morphology and distribution should be revised according to current standards. Currently, due to lack of reliable morphological and genetic data, almost all nominal species of Ceriodaphnia are considered as species groups rather than separate biological species, complicating the detection and description of new species of the genus. Here, we redescribe the morphology of Ceriodaphnia quadrangula (O.F. Müller, 1785) based on material close to the type locality in Denmark, and describe a new species of Ceriodaphnia from the Mediterranean region. Also, we provide a phylogenetic analysis using existing and novel sequences of mitochondrial DNA of the commonest species of the genus. Ceriodaphnia smirnovi sp. nov. can be easily distinguished from C. quadrangula via presence of the head pore and the structure of the second thoracic limb, the postabdomen and the ephippium. From other species of Ceriodaphnia known to date C. smirnovi sp. nov. can also be separated on ephippium structure and some other fine morphological features. Although distribution range of C. smirnovi sp. nov. must be clarified in the future based on analysis of more sampling points, most likely, it is restricted to the Mediterranean region. The phylogenetic analyses showed high divergence among 16 different clades (mean clade separation of 13±2.3 % (mean ± SD) and 20.7±2.1% for 16S and COI respectively). These clades belonged to 11 described species and 5 undescribed. The high intraspecific variability of some species indicates the possible existence of more undescribed species within present species groups.