Three new species of Sphaerodoridium (Polychaeta: Sphaerodoridae) from the Arctic Ocean

Three new species of the genus Sphaerodoridium (Polychaeta) from the Arctic Ocean are described and illustrated. They differ from other closely related species by having more than 10 longitudinal rows of stalked macrotubercles on the dorsum. S. evgenovi sp. n. is characterized by twelve rows of macrotubercles with stout, short columns which are always at the right angle to the dorsal surface and never overlap. The body is acorn-like with length up to 3.2 mm, the color in ethanol is from yellow to fallow. Sphaerodoridium kolchaki sp. n. is characterized by ten to fourteen rows of macrotubercles with thin, long columns, often lying on the dorsal surface and overlapping. The body is spindle-like, with length up to 6.0 mm. The color in ethanol is yellow. Eyes are present. Sphaerodoridium kupetskii sp. n. is characterized by up to twelve longitudinal rows of macrotubercles; the body is almond-like, straight, with length up to 1.4 mm. The color in ethanol is white. An identification key to the Sphaerodoridium species from the Arctic Ocean is provided.