Parasphaerolaimus pilosus sp. n.

(Figs 2–6; Table 1)

Diagnosis. Parasphaerolaimus pilosus sp. n. is characterized by moderately plump body, presence of lateral alae, long cervical setae, small amphids in males, and relatively short spicules.

Etymology. The species name is derived from the Latin “ pilosus ”, meaning “hairy”.

Holotype. VIETNAM: ♂, formalin-fixed, mounted on slide (MIMB 3 3138), in glycerin; deposited in the Zoological Museum IMB NSCMB FEB RAS; collected in Tien Yen Estuary, northern Vietnam, 21°18,997’ N, 107°36,075’ E; fine silty sands, water depth 0.5‒0.8 m.

Paratypes. VIETNAM: 1 ♂, 2 ♀♀, formalin-fixed, mounted on slides (MIMB 3 3139 – 33141); deposited in the Zoological Museum IMB NSCMB FEB RAS; collected in Tien Yen Estuary, northern Vietnam, 21°18,997’ N, 107°36,075’ E; fine silty sand, water depth 0.5‒0.8 m.

Type locality. Northern Vietnam, Tien Yen Estuary, 21°18,997’ N, 107°36,075’ E (Fig. 1); fine silty sand, water depth 0.5‒0.8 m.

Description. Male. Body stout, moderately long (1380‒1545 µm); tail conical. Cuticle finely striated with 20 µm wide lateral alae, which begin in the cervical region and extend to the base of tail (Fig. 6). Anterior end blunt. Inner labial setae short, six in number; outer labial setae short (3 µm), six; and cephalic setae longer (4.5‒5.5 µm), four. A circle of 12 subcephalic setae (4 µm in length) located right behind cephalic setae. Below, the circle of eight bunches of setae are situated, 2‒3 setae in each bunch. Subcephalic setae of next circle arranged more irregularly in groups of 1‒3. Cervical setae (26‒27.5 µm) numerous. Somatic setae (27‒30 µm) scattered along the body. Cheilostom with longitudinal ribs. Anterior part of gymnostom with 6 regular sclerotized plates. Posterior part with 3 dentate plates. Stegostom funnel-shaped with longitudinal ribs. Amphids circular, 11.5–12 µm in diameter or 30‒32% of corresponding body diameter. Distance from the anterior end to amphid 19.5–24 µm. Distance from the anterior end to nerve ring 40‒44% of pharynx length. Secretory-excretory pore located behind nerve ring. Pharynx muscular, cylindrical; cardia small. Anterior testis single, outstretched. Spicules short (ca 1 cloacal body diameter), slightly curved. Gubernaculum with small apophyses. Tail conical, 12–13% of total body length or 3.3 cloacal body diameters, with three caudal glands. Somatic setae irregularly distributed along the tail. Terminal setae (23– 25 µm in length), three in number.

Females. Similar to males but slightly bigger (1630–1800 µm). Amphids 6.5–7 µm in diameter or 10‒12% of corresponding body diameter. Distance from the anterior end to amphid 28 µm. Distance from the anterior end to nerve ring 149–173 µm. Single anterior outstretched ovary, 730 µm long. Vulva post equatorial, V = 55.5–67.1%. Tail conical, 11.5–12% of total body length or 2.6–3.8 anal body diameters.

Relationships. The described species is closely related to Parasphaerolaimus paradoxus and P. crassus. The new species is distinguished from P. paradoxus by a smaller body size (1380–1800 µm vs 2300–2400 µm), smaller a index (11–20 vs 37–49), and longer spicules (54–56 µm vs 47.5 µm). Parasphaerolaimus pilosus sp. n. is distinguished from P. crassus by shorter cervical setae (26–28 µm vs 30–40 µm), relatively larger amphids in male (30–32% vs 25% of the corresponding body diameter), more curved and bigger spicules (54–56 µm vs 51 µm), and smaller gubernacula (18–20 µm vs 29 µm).