Meristoderes okhotensis sp. nov. - The first deepwater representative of kinorhynchs in the Sea of Okhotsk (Kinorhyncha: Cyclorhagida)

A new species of echinoderid kinorhynchs, Meristoderes okhotensis sp. nov. collected from oxidized brown silt at Kuril Basin, the deepest depression of the Sea of Okhotsk, northwestern Pacific, is described and illustrated using light and electron microscopy. This new representative of the most recently described genus Meristoderes from the family Echinoderidae is characterized by the structure of the second trunk segment consisting of an externally closed cuticular ring with indistinct intracuticular tergosternal junctions which are remarkably curved. This segment also bears pairs of subdorsal, laterodorsal and ventrolateral adhesive tubules. Trunk segment 5 with tubules in lateroventral position. Aciculate lateroventral spines on trunk segments 6-9. Meristoderes okhotensis sp. nov. is the only representative of the genus with two middorsal spines, on trunk segments 6 and 8. This species is well recognized by its exceptionally long tergal extensions of trunk segment 11, some of the longest within all kinorhynch species. Meristoderes okhotensis sp. nov. appears the deepest representative of the family Echinoderidae described so far. It constitutes the eighth species and the first deepwater representative of the genus Meristoderes. Also, this is the first species of kinorhynchs described from the Sea of Okhotsk. A key to the species of the genus Meristoderes is proposed.