Mixtacandona thessalica, a new species of ostracod (Crustacea, Ostracoda) from a sulfidic cave in central Greece

The genus Mixtacandona Klie, 1938 (Crustacea, Ostracoda, Candonidae) includes 21 living non-marine species, all subterranean, with Palearctic distribution. Here we report on Mixtacandona thessalica sp. nov., collected in a sulfidic cave in central Greece. It can be considered an extremophile species because of its ability to thrive in an environment with high concentrations of sulfide and reduced chemical compounds. Mixtacandona thessalica sp. nov. belongs to the species group laisi–chappuisi, one of the five groups in which species of the genus are conventionally placed. A detailed morphological description of the valves and the soft parts of the new species is offered. In addition, COI and 28S genetic markers were sequenced. Mixtacandona thessalica sp. nov. is easily distinguishable from the other species in the genus by its peculiar carapace outline and the marked sexual dimorphism of the posterior margin of valves, as well as by details of chaetotactic characters. The discovery of Mixtacandona thessalica sp. nov. increases the number of non-marine ostracod species known from Greece, which is still rather scarce compared to other Mediterranean countries due to the scarcity of studies. Ten hypogeal species of living ostracods have already been reported from Greece, six of which are considered endemic, and among them three belong to the genus Mixtacandona. It is stressed that a comprehensive review of this genus by combining a thorough morphological approach and molecular techniques, is most needed to assess its phylogenetic relationships within the family Candonidae.