Redescription of Antarctic eutardigrade Dastychius improvisus (Dastych, 1984) and some remarks on phylogenetic relationships within Isohypsibioidea

In the present paper, we examined the type material as well as newly collected specimens of the rare Antarctic eutardigrade species – Dastychius improvisus. Based on the available material, we prepared a full re-description of this species emending its description with new morphometrical characters. We conducted also phylogenetic analyses based on 18S and 28S rRNA sequence data and showed the position of the genus Dastychius in the family Isohypsibiidae. Moreover, we indicated that phylogenetic relationships within the superfamily Isohypsibioidea are still unresolved. This problem is mainly related to the relatively limited number of available sequences for the species from Isohypsibioidea and incorrectly identified sequences deposited in genetic databases, e.g. from the genus Eremobiotus. Finally, we also discussed the status of several members of Isohypsibioidea.