Background: Kinorhynchs are marine, microscopic invertebrates inhabiting the seafloors. Their segmented trunk equipped with spines and processes has inspired scientists to give them the common name "mud dragons." Even though kinorhynchs have been known since the 19th century, less than 300 species are known to science, and it is still considered a largely understudied animal group-in particular in the Arctic, from which only 23 species are known so far.

Methods: Samples were collected at eight stations around Svalbard and in the fjords of Spitsbergen. Meiofauna was extracted from the sediment cores with LUDOX centrifugation method, and kinorhynchs were picked up and mounted for light- and scanning electron microscopy.

Results: Four new species of the kinorhynch family Pycnophyidae are described from Svalbard: Cristaphyes dordaidelosensis sp. nov., C. glaurung sp. nov., C. scatha sp. nov., and Pycnophyes ancalagon sp. nov. The new species are generally recognized by their distribution of setae along the trunk segments.

Discussion: After the discovery of the new species, Pycnophyidae becomes with 14 species the most diverse kinorhynch genus in the Arctic, closely followed by Echinoderidae with 13 species. So far, these are the only kinorhynch families with an Arctic distribution.