A new species of the rare genus Sphenoderes (Cyclorhagida, Kinorhyncha), with differential notes on S. indicus Higgins, 1969

A new species of the rarely recorded kinorhynch genus Sphenoderes was collected in the Korea Strait and East China Sea. The new species, Sphenoderes poseidon sp. nov., is distinguished by the presence of lateroventral cuspidate spines on segments 5 and 9 only, opposed to cuspidate spines on segments 5, 8 and 9 as found in S. indicus. The new species is furthermore characterized by having the special head aperture that is diagnostic for species of Sphenoderes, but yet possessing a segment 1 composed of a single, closed cuticular ring, rather than a dorsal, a ventral and two lateral plates as found in S. indicus. The description of Sphenoderes poseidon sp. nov. includes the first scanning electron microscopical examinations of cuticular details in a species of Sphenoderes. The new information is discussed and a comparison is made with the putative closely-related species S. indicus, as well as with other species more generally across the Kinorhyncha.