Discovery of Two New Deep-Sea Desmoscolex Species (Nematoda: Desmoscolecidae) with Wing-like Cephalic Setae from the Ulleung Basin, the East Sea, Korea †

This study describes two new species of the subgenus Desmoscolex (Nematoda: Desmoscolecidae) from deep-sea habitats in the Ulleung Basin, the East Sea, Korea, located in the NorthWest Pacific Ocean. Both species exhibit cephalic setae with wing-like appendages—a rare trait documented in only a few species of this subgenus. Desmoscolex (Desmoscolex) globiceps sp. nov. is characterized by a rounded head covered with concretion particles, wing-like cephalic setae equipped with thin, flap-like membranes, and oval amphidial fovea that cover most of the head. The body is composed of 17 main rings, bearing slender somatic setae that taper to an open tip and a conical terminal ring that elongates to a short spinneret. Females of this species lack subventral setae on the 14th main ring. Desmoscolex (Desmoscolex) ovaliceps sp. nov. features an oval head covered with foreign particles, wing-like cephalic setae with thin, flap-like membranes, and oval amphids encompassing much of the head. This species also has a body with 17 main rings, with subdorsal setae gradually tapering toward the tip, which is slightly differentiated from the rest, and shorter subventral setae ending with an open distal tip. The terminal ring is conical, slightly tapered, and terminates in an uncovered spinneret. Detailed morphological descriptions of both species are provided, incorporating scanning electron microscopy (SEM) and differential interference contrast (DIC) images. A comparative analysis with previously described taxa is included, along with a pictorial key to assist in the identification of related species, contributing to a deeper understanding of morphological diversity within the subgenus Desmoscolex.