A New Species of Freshwater Tardigrades from Disko Island (Greenland) Increases an Unsolved Paradox in Tardigrade Systematics

Abstract

During the “Workshop on Arctic tardigrades” at the Danish Arctic Station (Qeqertarsuaq, Disko Island, Greenland) an undescribed species of Dactylobiotus was found in freshwater sediments of the Isunngua spring. We have the honour and pleasure to describe this new taxon that we dedicate to all participants of that symposium, naming the species Dactylobiotus octavi sp. n. The animals appear similar to Dactylobiotus dispar and Dactylobiotus haplonyx with the presence of a very short secondary branch in the claws of the first three pairs of legs, but they differ from these species in the size of claw and buccal tube width. This new species also has peculiar ornamented eggs. The eggshell consists of bowl-like processes, each one surrounded by a band of fine pores. A morphological parsimony analysis to identify phylogenetic relationships among D. octavi sp. n. and the other Dactylobiotus species was performed, obtaining inconclusive results. The discovery of this new species increases an unsolved paradox in tardigrade systematics related to the presence of closely related species which share a very similar morphology of the animals but clearly differ in their egg morphology, while, conversely, there are species belonging to different evolutionary lines that have similar eggs, but very different adult morphology. The finding of D. octavi sp. n. increases the already high number of species found in Disko Island and once again underlines the importance of tardigrades in the biodiversity of the Arctic area.