In May 2023, a free-living marine nematode species from the genus Parapinnanema was identified in the subtidal zone of Ulleungdo Island, the East Sea, Korea. Specimens were collected using the Smith-McIntyre Grab. These specimens exhibited close similarities to Parapinnanema imbricatum from the sublittoral of Moneron Island, particularly in terms of general characteristics, such as the detailed structure of the buccal cavity, the complex and ringed structure of the cuticle, the copulatory apparatus, spinneret, and the female genital system. However, the Korean specimens of Parapinnanema imbricatum also displayed distinctive features compared to the original description, including a relatively elongated body (3,317-4,339 μm vs. 3,100-4,200 μm) and a narrower body width (66-77 μm vs. 71-85 μm). Additionally, the diameter of the head was relatively shorter (24-29 μm vs. 28-36 μm). This paper offers a comprehensive morphological description, along with illustrations and DIC photomicrographs, of P. imbricatum from Korean waters.

The subgenus Tricoma Cobb, 1894 comprises free-living marine nematodes encompassing a total of 83 validated taxa. Within this diversity, twenty-one taxa thrive in the deep sea, while twenty-three are found in coral reefs, flat areas, or green algae. Additionally, eleven taxa inhabit the sublittoral zone at depths exceeding 10 meters, and the remaining taxa are situated on beaches, coasts, or in habitats lacking detailed information. In the course of a survey focused on the East Sea free-living marine nematodes, we identified four new and two previously unrecorded species belonging to the subgenus Tricoma. Specifically, two new species, Tricoma (Tricoma) breviseta sp. nov. and T. (T.) donghaensis sp. nov., were discovered in mud-sandy sediment in deepsea environments below 2000 meters within the Ulleung Basin and Hupo Bank. Two previously unrecorded species [T. (T.) paralucida Decraemer, 1987 and T. (T.) similis Cobb, 1912] and the two newly found species [T. (T.) longicauda sp. nov. and T. (T.) ulleungensis sp. nov.] were obtained from subtidal coarse sand at a depth of 20 meters during a survey of the waters surrounding Ulleungdo Island. The distribution and information on validated taxa within the subgenus Tricoma were systematically collected, reviewed, and cataloged. Detailed morphological features and illustrations of Tricoma species from Korea were provided through the use of differential interference contrast microscopy.

During a survey of free-living marine nematodes of Korea, two new marine desmoscolecid nematodes belonging to subgenus Quadricoma Filipjev, 1922 were discovered. Tricoma (Q.) jejuensis sp. nov. and T. (Q.) unipapillata sp. nov. are described based on specimens obtained from washings of coarse sediments from eastern and southern coasts of Korea. Tricoma (Q.) jejuensis sp. nov. is characterized by having 33 quadricomoid body rings and inversion at main ring 23, pentagonal head with truncated anterior end, a pair of ocelli situated at main ring 6, somatic setae comprising of 8 pairs of subdorsal setae and 12 pairs of subventral setae, and relatively short spicules (42-46 μm long). Tricoma (Q.) unipapillata sp. nov. is characterized by 44 quadricomoid body rings and inversion at main ring 32, somatic setae comprising of 7 pairs of subdorsal setae and 10 pairs of subventral setae, globular head truncated anterior end, relatively short and stumpy cephalic setae with cuticular flange, one single naked ventral median genital papillae situated on main ring 20, and spicules with a proximally marked capitulum. Detailed morphological descriptions and illustrations of these two new species are provided in this study.

Two new free-living marine nematodes of the genus Belbolla Andrássy, 1973 belonging to family Enchelidiidae are newly described based on specimens obtained from a shallow subtidal sediment of the western and southern outermost islands of Korea. Belbolla koreensis sp. nov. differs from other species of the genus by the combination of the following characteristics: longer body length (3,080-3,462 μm long), eight oesophageal bulbs in the posterior region of pharynx, well-developed two winged precloacal supplements (anterior precloacal supplement slightly longer than posterior one: 47-59 μm vs. 43-46 μm long), strongly arcuated, very thick, L - shaped spicule (122- 127 μm long, 1.7-1.9 anal body diameter (a.b.d.) long) with three separated blunt distal tips, and well-developed relatively long cylindrical shaped gubernacular apophysis with blunt teeth covering two thirds of the dorsal margin (57-58 μm long, 0.8-0.9 a.b.d. long). Belbolla hoonsooi sp. nov. is characterized by the following combination of characteristics: longer body length (3,494 μm long), eight oesophageal bulbs in the posterior region of pharynx, well-developed two winged precloacal supplements (anterior precloacal supplement slightly longer than posterior one: 43 μm vs. 36 μm long), strongly arcuated, L - shaped spicule (119 μm long, 1.5 a.b.d. long) with three separated blunt distal tip, and well-developed relatively long inverted triangle shaped gubernacular apophysis with blunt teeth covering half of the dorsal margin (45 μm long, 0.6 a.b.d. long). Detailed morphological characteristics and illustrations of two new Belbolla nematodes from the Korean seawaters were provided by differential interference contrast microscopy. Comparative tables on biogeographical and morphological characteristics of Belbolla species are also provided herein.

A new free-living marine nematode species of the genus Belbolla Andrássy, 1973 belonging to the family Enchelidiidae is described based on specimens collected from the sediment of a subtidal benthic environmental habitat in the East Sea, Korea. Belbolla wonkimi sp. nov. differs from its congeners by the combination of the following characteristics: a relatively long body (3263-3396 μm), the absence of ocelli, nine oesophageal bulbs in the posterior pharynx, well-developed two winged precloacal supplements, longer spicule length (115-130 μm, 1.6-1.8 anal body diameter long), and a triangle-shaped shorter gubernacular apophysis (17-18 μm). Comparative tables on the biogeographical and morphological characteristics of Belbolla species are presented. A DIC (differential interference contrast) photomicrograph of the new species is also provided. This is the first taxonomic report on the genus Belbolla from Korean waters.