A new species of harpacticoid copepod of the family Canthocamptidae, Maraenobiotus supermario sp. nov. is described. The new species was found in interstitial waters of the moss tundra of the Lena River Delta, Siberia. This species belongs to the vejdovskyi-species group. The new species differs from its congeners in the apical caudal setae lacking a bulbous proximal part, and in the unique structure of the mandibular palp with only one seta. We also present detailed figures and description of sensilla and pores on the somites surface, which could be used in the future to diagnose and solve taxonomic issues of this complex genus.