Ptychogastria polaris is a cold-water hydrozoan medusa showing bipolar distribution. Although it occurs in the temperate Atlantic and Pacific Oceans, the medusa was recorded only in deep shelf waters with stable low temperatures in temperate zones (Panteleeva et al., 1999). The bell of live medusae is hemispherical, and reaches approximately 3 cm in diameter. The stomach with bright-pink coloration consists of eight lobes along the radial canals, and eight pairs of white gonads are situated above the stomach lobes and along their sides. There are two kinds of the solid tentacles distributed along the bell margin: longer extensible filiform tentacles and shorter suckered ones. The species is often found sitting on muddy bottoms or attaching to rock surfaces by using suckered tentacles (Stuebing & Piepenburg, 1998; Panteleeva et al., 1999).