Gordionus chinensis and Gordionus kii sp. nov. (Nematomorpha: Gordiida), New Reports of the Genus Gordionus in Japan

Abstract

Eleven species representing four genera of freshwater horsehair worms (Gordiida, Nematomorpha) have been known from Japan. The presence of representatives of the genus Gordionus was likely, but until now the available material did not allow such a determination. We here report several specimens of Gordionus chinensis (Villot, 1874) from the Yumitehara River in Nara Prefecture, which differ only in one minute detail from the original description of this species. Characteristic for this species are sparse knoblike structures occurring between the cuticular areoles. In the Japanese specimens, these knobs occur at the midpoint of the common border between pairs of neighbouring areoles and also in the corners where several areoles meet, but in the description of the Chinese holotype, such knobs occur only in the former position. One male specimen from the same locality differs distinctly from the others in having shorter bristles flanking the cloacal opening and longer spines on the inner sides of the tail lobes. We regard it as representing a new species, herein named Gordionus kii.