Paracomesoma minor Gagarin & Tu, 2014, sp. n.

Paracomesoma minor sp. n.

(Figs 1, 2; Table 1)

Type material. Holotype male, slide reference number 102/38, deposited in the helminthological museum of the Russian Academy of Sciences (RAS), Institute of Ecology and Evolution, Center for Parasitology, RAS (Moscow, Russia).

Paratypes. One male deposited in the helminthological museum of RAS, Institute of Ecology and Evolution, Center for Parasitology, RAS (Moscow, Russia). Two females deposited in the nematode collection in the Institute Ecology and Biological Resources, Vietnamese Academy of Sciences and Technology, Hanoi, Vietnam.

Measurements. Table 1.

Type habitat and locality. South China Sea, littoral zone of coastal Vietnam. Latitude: 21º15.170ʹ–21º15.360ʹ; Longitude: 107º23.250’–107º23.796, depth 1.0– 2.5 m, sand, with 20–24 ‰ salinity.

Etymology. The specific epithet means “small” or “small size”.

Description. Male. Body slender. Cuticle annulated and marked with fine irregular punctation. Punctations on lateral part of body rather larger. Cuticle in the vulva region about 1µm thick. Somatic setae short, numerous. Labial region narrow, not set off. Inner labial sensillae papilliform. Six outer labial sensillae in the shape of setae of identical size, 7.0–7.2 µm long. Four cephalic sensillae in the shape of setae 14.2–14.5 µm long, 1.1–1.2 times as long as labial region width. Both circles of setae close together. Cervical setae 9–11 µm long, arranged in four transverse files of three to four setae and situated 21–25 µm from anterior body end (1.7–1.9 labial region width). Amphidial fovea spiral with 3.5 turns, situated at a distance of 4–5 µm from anterior body end. Diameter of amphidial fovea 53–55 % of corresponding body diameter. Stoma in the shape of funnel. Three small teeth in stoma. Pharynx slender, muscular, swollen proximally, forming elongate bulb. Cardia small, in lumen of intestine. Ventral gland compact, situated slightly below of cardia level. Excretory pore posterior to nerve ring, at 93–96 µm from anterior body end.

Gonads diorchic; testes opposite and outstretched. Spicules thin and long, 4.2–4.3 times as long as cloacal body diameter. Spicule capitulum small, poorly developed. Gubernaculum in shape of comparatively short and wide, conical plate. Eight or nine precloacal ventromedial supplements present, in the form of small, weakly visible papillae. Tail slender, with proximal conical and distal cylindrical portions, gradually merging with one another. Terminus of tail swollen with subterminal setae. Caudal setae short, numerous. Caudal glands present; spinneret short, conical.

Female. General appearance, structure of cuticle, and anterior body end similar to that of male. Cuticle annulated and marked with irregular punctation. Somatic setae short, numerous. Labial region not set off. Inner labial sensillae papilliform. Six outer labial sensillae in the shape of setae of identical size, 7.0–7.5 µm long. Four cephalic sensillae in the shape of setae 14.0–14.5 µm long. Both circles of setae close together. Cervical setae 8–10 µm long, arranged in four transverse files of three to four setae and situated at distance of 26–30 µm from anterior body end. Amphidial fovea spiral, with 3.5 turns. Diameter of amphidial fovea 49–51% of corresponding body diameter. Stoma funnel-shaped, with three small teeth. Pharynx slender, muscular, swollen proximally, forming elongate bulb. Ventral gland situated at level of anterior portion on intestine. Excretory pore posterior to nerve ring, at distance 97–101 µm from anterior body end. Rectum 0.6–0.8 times as long as anal body diameter.

Reproductive system didelphic, amphidelphic; ovaries outstretched. Both ovaries situated to left side of intestine. Oocytes numerous, arranged in one or two rows. Uterus filled with sperms. Vagina short, with muscular walls. Vulva crescent-shaped. Vulva lips not sclerotized, not protruding outside the body contour. Tail slender with proximal conical and distal cylindrical portions, gradually merging with one another. Tail terminus with three subterminal setae 7–8 µm long. Three caudal glands terminating in one chamber and opening through a short, conical spinneret.

Diagnosis. Paracomesoma minor sp. n. is characterized by its small size and comparatively slender of body (L = 961–1142 µm, a = 30–38), presence of six outer labial setae of the identical size 7.0–7.5 long and four cephalic setae 12.1–12.7 µm long (1.1–1.2 labial region width); cervical setae 8–11 µm long, arranged in four transverse files of three to four setae; amphidial fovea spiral with 3.5 turn; slender pharynx, swollen proximally, forming elongate bulb; thin and long spicules 93–98 µm long (4.2–4.3 cloacal body diameter), comparatively short and wide gubernaculum; presence of 8–9 precloacal ventromedian supplements in the shape of small papillae and slender tail with subterminal setae.

Differential diagnosis. The genus Paracomesoma was established by Hope & Murphy in 1972. At present, the genus contains 15 valid species (Jensen 1979, Tu et al. 2013, present article). Five species have been found in Vietnam: P. curvitatum Gagarin & Thanh, 2006; P. elegans Gagarin, Nguyen Vu & Thanh, 2009; P. lissum Gagarin & Thanh, 2009; P. paralongispiculum Tu et al. 2013, and P. minor sp. n. Paracomesoma minor sp. n. groups with other species of the genus Paracomesoma which have six outer labial setae of identical size: P. dubium (Filipjev, 1918) Hope & Murphy, 1972, P. curvispiculatum (Allgén, 1959) Hope & Murphy, 1972, P. longispiculum (Timm, 1961) Hope & Murphy, 1972, P. curvitatum, P. elegans, P. lissum, and P. paralongispiculum. The new species is morphologically close to P. elegans and P. lissum. It differs from the former in the shorter body (L = 961–1142 µm versus L = 1092–1320 µm in P. elegans), longer and more slender tail (c = 7.8–8.7, c’ = 5.0–5.9 versus c = 10.5–13.2, c’ = 3.4–5.1 in P. elegans), longer cephalic setae (14.0–14.5 µm long versus 3.5–4.5 µm in P. elegans), presence of cervical setae and shorter spicules (93–98 µm long versus 125–165 µm long in P. elegans) (Gagarin & Thanh 2009). From P. lissum it differs in the shorter body (L = 961–1142 µm versus L = 1338–1784 µm in P. lissum), longer cephalic setae (14.0–14.5 µm long versus 6.0–7.0 µm in P. lissum), presence of cervical setae and smaller number of precloacal supplements in males (8–9 supplements versus 45–47 supplements in P. lissum) (Gagarin & Thanh 2009).