Viscosia sinica Sun, Gu & Huang, 2025, sp. nov.

Viscosia sinica sp. nov. Figs 4, 5, Table 1 Dianosis. Relatively large amphidial fovea, about 80 % corresponding body diameter wider in males and 53–62 % in females. Cephalic setae 5–7 µm long. Tail conico-cylindrcal with swollen horseshoe-shaped tip. Spicules slender, slightly curved ventrally, not cephalate proximally. 10–12 setae surrounding the cloaca, each 3–4 µm long. Holotype and paratype material. Four males and two females were measured. Holotype male 1 on slide RZ 080123-4. Paratype 1 (male 2) on slide YST 24251-2, paratype 2 (male 3) on slide YST 24381-11, paratype 3 (male 4) on slide YST 24253-1, paratype 4 (female 1) on slide RZ 0803123-4, paratype 5 (female 2) on slide YST 2418-12. Type locality and habitat. Holotype and paratype 4 (female 1) were collected from the surface layer of fine sand sediment on an intertidal beach along the Rizhao coast of the Yellow Sea (35°34'21"N, 119°39'29"E). The other paratypes were all collected from the surface layer of silt sediment on an intertidal beach of Huangdao along the Yellow Sea (31°44'53"N, 121°55'43"E). Etymology. The species epithet refers to the country of origin, China. Measurements. All measurement data are given in Table 1. Descriptions. Males. Body relatively slender. Cuticle smooth, without somatic setae. Labial region spherical, demarcated by slight constriction. Six lips, each bearing a single internal labial papilla. Six outer labial setae and four cephalic setae in a single circle, equal in length. Amphidial fovea relatively large, pocket-shaped, 9–11 µm wide, about 80 % corresponding body diameter, and 5–6 µm deep, located at level of the middle of buccal cavity. Buccal cavity 16–29 µm deep and 8–10 µm wide, with three teeth. Right ventrosublateral tooth larger than left ventrosublateral tooth and dorsal tooth. The tip of right ventrosublateral tooth at the same level with outer labial and cephalic setae. The height of left ventrosublateral tooth and dorsal tooth are almost equal. Pharynx cylindrical, widening slightly towards posterior extremity. Cardia conical, about 15 µm long, surrounded by intestinal tissue. Nerve ring located approximately halfway down length of pharynx. Secretory-excretory system and excretory pore not observed. Reproductive system with two opposed and outstretched testes located to the right of intestine. Spicules slender, slightly curved ventrally, not cephalate proximally. Gubernaculum absent. 10–12 setae surrounding the cloaca, each 3–4 µm long. Tail conico-cylindrical, with swollen horseshoe-shaped tip. Caudal setae absent. Three caudal glands extending anteriorly to tail region. Spinneret present. Females. Similar to males in the most morphological characteristics but amphidial fovea slightly smaller, 53–62 % corresponding body diameter wider, and buccal cavity slightly shallower (21–29 µm versus 16 µm deep). Reproductive system with two opposed and reflexed ovaries both located to the right of intestine. Demanian system indistinct. Vulva located at mid-body. Differential diagnosis and discussion. Viscosia sinica sp. nov. is characterized by relatively large amphidial fovea, conico-cylindrcal tail with horseshoe-shaped tip, spicules slender, slightly curved ventrally, not cephalate proximally, 10–12 setae surrounding the cloaca, each 3–4 µm long. The new species resembles V. brachylaima Filipjev, 1927 and V. filipjevi Paramonov, 1929 in tail shape, but differs from V. brachylaima by larger amphidial fovea (80 % versus 30 % corresponding body diameter) and higher value of de Man ratio a in males (61.9–72.8 versus 42.5). The new species differs from V. filipjevi which description is based only in females by larger amphidial fovea (wider than width of buccal cavity versus narrower than width of buccal cavity), and smaller body size (1.46–1.65 mm in body length and 28–31 µm maximum body diameter in females versus 2.17–2.20 mm in length and 40.5–48.6 µm maximum body diameter in V. filipjevi). The new species is also similar to V. elegans (Kreis, 1924) Lorenzen, 1981 in body size and shape, but differs by larger amphidial fovea (80 % versus 33 % corresponding body diameter) and horseshoe-shaped tail tip. The new species differs from V. media sp. nov. in having deeper buccal cavity with slender teeth in males (21–29 µm deep versus 15–18 µm with stubby teeth), larger amphidial fovea (versus invisible), and different tail shape (conico-cylindrical with swollen horseshoe-shaped end versus conical). Viscosia sinica sp. nov. is distinguished from all other known species of the genus by its relatively large amphidial fovea, 5–7 µm cephalic setae, and conico-cylindrical tail with swollen horseshoe-shaped end.