A new species of Tantulocarida was found off the coast of Disko Island, West Greenland. The new species, Arcticotantulus kristenseni sp. nov., is exclusively found on an as yet undescribed species of Brady a Boeck, 1873 (Copepoda, Harpacticoida) caught at depths of 200 m off the coast in muddy sediments. A total of 44 individuals were found, and 38 were examined by use of LM and SEM; these represented different stages of the life cycle: tantulus larvae, developing males, parthenogenetic females, and what may be only the third record of a developing sexual female. Arcticotantulus kristenseni is tentatively placed in Deoterthridae based on the mode of formation of the male trunk sac, the pattern of ornamentation on the tergites and cephalic shield, and the number of setae on the thoracopods and caudal rami. It is suggested that the genus Arcticotantulus Kornev, Tchesunov & Rybnikov, 2004 is removed from Basipodellidae and placed in Deothertridae instead, in accordance with the mode of trunk sac development in males and the absence in the latter family of a cephalic rostrum. Various internal anatomical features were examined, including the tubular structures inside the head of the tantulus larvae. The first live photographs of any species of Tantulocarida are presented. This is also the first report on Tantulocarida from West Greenland.