A study of intertidal habitats on Jejudo Island, Korea led to the identification of two new species, Desmoscolex (Desmoscolex) jejuensis sp. nov. and Desmoscolex (Desmoscolex) longispiculatus sp. nov., belonging to the subgenus Desmoscolex. Desmoscolex (D.) jejuensis sp. nov. is distinguished by the presence of 18 main rings, with males missing the 8th, 10th, and 14th subventral setae with the 2nd and 15th setae shifted laterally. In females, the 6th, 8th, 10th, and 14th subventral setae are absent. Conversely, D. (D.) longispiculatus sp. nov. exhibits 17 main rings with a typical somatic setae arrangement along with notably elongated spicules and the 14th and 15th subventral setae shifted laterally or slightly subdorsally. Both species are characterized by relatively long and slender cephalic setae. Detailed illustrations and high-magnification micrographs were produced using differential interference contrast (DIC) microscopy and scanning electron microscopy (SEM) to facilitate morphological comparisons between these new species and related taxa. Furthermore, a comparative trait table and a pictorial key are provided to clearly differentiate these new species from morphologically similar taxa. These findings contribute to the understanding of nematode biodiversity and contribute to the broader knowledge of Desmoscolex diversity in Korean coastal ecosystems.

This study describes two new species, Desmoscolex (Desmoscolex) delticeps sp. nov. and Desmoscolex (Desmoscolex) obtusiseta sp. nov. Belonging to the subgenus Desmoscolex, they were discovered in subtidal habitats along the coast of Korea. Detailed morphological analyses of the two new species were conducted using differential interference contrast (DIC) microscopy and scanning electron microscopy (SEM). D. (D.) delticeps sp. nov. was collected from subtidal zones near Ulleungdo Island. It is characterized by a broadly triangular head with robust cephalic setae and centrally positioned oval amphidial fovea. Its somatic setae are arranged in 17 main rings. Its conical terminal ring ends in a long, uncovered spinneret. D. (D.) obtusiseta sp. nov. was collected from distant subtidal zones along the western coast. It is characterized by short, blunt cephalic setae situated on peduncles, a flattened anterior head, and an oval amphidial fovea with a central pore. Its somatic setae are arranged in 17 main rings. Its terminal ring tapers ventrally, ending in a short spinneret. This study highlights distinctive cephalic setae morphologies of these species, providing a deeper understanding of nematode diversity in Korean subtidal zones and contributing to the advancement of marine nematode taxonomy.