A new species of cestodes from the intestine of crabeater seal, inhabiting the Antarctic waters, is described. A new subfamily, Baylisiinae subfam. n., which includes the species Baylisia baylisi Markowski, 1952, is erected for the new species. The new species is extremely polygonadal. In each proglottide of the strobile of different individuals there are from 149 to 307 sexual complexes. The length of hind proglottides is 4.3. to 18.5 cm. Unlike other polygonadal cestodes, sexual complexes of the described species are arranged in the proglottide in two longitudinal rows, alternating irregularly now from the left, now from the right side. The longitudinal axis of each sexual complex is directed transverse proglottide. Ovaries are groupped along the median line of the proglottide, and genital openings are approximately in the middle of lateral fields, on their ventral surface.
