Viscosia media, Sun & Gu & Huang, 2025

Viscosia media sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , Table 1 View Table 1

Diagnosis.

Body slender, medium size in the genus. Heavily cuticularized and relatively shallow buccal cavity with three stubby teeth, and a right ventrosublateral tooth massive. Cephalic setae 7–8 µm long. Amphidial fovea invisible. Spicules slender, almost straight, cephalated proximally and conical distally. Tail conical, straight in males, slightly bent ventrally in females.

Holotype and paratype material.

Four males and two females were measured. Holotype male 1 on slide RZ 080312-9 GoogleMaps . Paratype 1 (male 2) on slide RZ 080310-3 GoogleMaps , both paratype 2 (male 3) and paratype 3 (male 4) on slide RZ 0803123-4 GoogleMaps , paratype 4 (female 1) on slide RZ 080312-9 GoogleMaps , and paratype 5 (female 2) on slide RZ 0803123-4 GoogleMaps .

Type locality and habitat.

Holotype and paratypes were all collected from the surface layer of fine sand sediment on an intertidal beach along the Rizhao coast of the Yellow Sea, China (35°34'21"N, 119°39'29"E).

Etymology.

Species epithet media refers to the medium body size of this species within the genus.

Measurements.

All measurement data are given in Table 1 View Table 1 .

Descriptions.

Males. Body medium in size, and slender, tapering slightly towards both extremities. Cuticle smooth. Cervical setae 4–6 µm long, sparse, present only in the anterior portion of pharyngeal region. Cephalic region truncated, continuing with body contour. Six lips, each bearing a single inner labial papilla. Six outer labial setae and four slightly longer cephalic setae in a single circle. Outer labial setae 6–7 µm long, cephalic setae 7–8 µm long. Amphidial fovea invisible. Buccal cavity heavily cuticularized, relatively shallow, 15–18 µm deep and 7–9 µm wide, with three stubby teeth. Right ventrosublateral tooth massive and 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, surrounded by intestinal tissue. Nerve ring located pre-mid of length of pharynx. Secretory-excretory system present; excretory pore located slightly posterior to nerve ring, 160–170 µm from anterior end. Ventral gland located at anterior part of the intestine.

Reproductive system with two opposed and outstretched testes located to the right of intestine. Sperm cells oval or irregularly square, 12–16 µm long and 8–10 µm wide. Spicules slender, almost straight, cephalated proximally and conical distally. Gubernaculum absent. Tail conical, narrowing abruptly immediately posterior to cloaca and directed slightly dorsally, without caudal setae. Three caudal glands extending anteriorly to tail region. Spinneret present.

Females. Similar to males in most morphological characteristics but there are less cervical setae, and tail slightly bent ventrally. Reproductive system with two opposed and reflexed ovaries both located to the right of intestine. Eggs very long, can be up to 220 µm long. Demanian system simple, consisting of a sac-like prolongation of the ovary at the reflexed point of the ovary and a duct-shaped osmosium. Vulva located at mid-body.

Differential diagnosis and discussion.

Viscosia media sp. nov. is characterized by heavily cuticularized and relatively shallow buccal cavity with three stubby teeth, right ventrosublateral tooth massive, cephalic setae 7–8 µm long, amphidial fovea invisible, spicules slender, almost straight, cephalated proximally and conical distally, tail conical, straight in males, slightly bent ventrally in females. The new species is similar to V. epapillosa Platonova, 1971 in the deep of buccal cavity and length of cephalic setae, but differs by the wider head diameter (16–18 µm versus 11–13 µm), buccal cavity with heavily cuticularized parallel walls (versus buccal cavity wider in the middle and narrower at the ends), having cervical setae (versus absent in the latter species), spicules enlarged proximally (versus not enlarged), and a conical tail almost straight in the males (versus conico-cylindrical tail bent in the latter species). The new species is also similar to Viscosia pygmaea Nguyen Vu Thanh & Gagarin, 2013 in the tail shape, but differs from V. pygmaea by the longer body length (1458–1620 µm versus 838–992 µm), longer cephalic setae (7–8 µm versus 3–3.5 µm), shallower buccal cavity with stubby teeth (1 head diameter versus 1.5 head diameters in depth with slender teeth), amphidial fovea invisible (versus obvious and located close to the base of buccal cavity), and the different spicule shape (slender with cephalated proximal end and tapering distally end versus conical and tapering off). Viscosia media sp. nov. can be differentiated from all other species of the genus by its heavily cuticularized and relatively shallow buccal cavity with stubby teeth, 7–8 µm cephalic setae, and a conical tail. The basic morphological characteristics of the valid species with similar size to the new species in the genus are compared in Table 2 View Table 2 .