Paracomesoma zhangi Huang & Huang, 2018

Huang, Mian, Jia, Susu & Huang, Yong, 2018, One new species and one new record of the species of the family Comesomatidae (Nematoda: Chromadorida) from the South China Sea, Zootaxa 4504 (1), pp. 119-127 : 124-127

Paracomesoma zhangi Huang & Huang, 2018

( Figs 3–4 )

Material examined. Five males and three females were collected from Stations NHqzhx1. ♂ 1, ♂ 2, on slide NH 17- 5-8-28-1 (bottom layer); ♂ 3, ♂ 4 and ♀ 2 on slide NH 17-2-5-28-3 (subsurface layer); ♂ 5 on slide NH 17-2-5-73 -1 (subsurface layer); ♀ 1 on slide NH 17-5-8-28-4 (bottom layer); ♀ 3 on slide NH 17-2-5-28-1 (subsurface layer), respectively.

Locality and habitat. Subtidal muddy sediment at Station NHqzhx1 of Qiongzhou strait (20°3′53″ N; 110°21′5″ E, water depth 13 m).

Measurements. Table 2.

Description. Males. Cuticle with fine transverse rows of punctuations, without lateral differentiation. Head slightly setting off by a contraction at the level of cephalic setae. Buccal cavity 12–14 µm deep, composed of two parts, the anterior part cup-shaped, with three small teeth, the posterior part in form of a cuticularized tube as long as the labial region width. Head sensilla arranged following the 6+6+4 pattern. Inner labial sensilla papilliform; six outer labial sensilla setiform, 4 µm long. Cephalic sensilla setiform, 9–10 µm long, located 0.5 head diameter from the anterior end. Somatic setae (about 4 µm long) scattered and numerous. Multispiral amphideal fovea with three turns, located closely behind the cephalic setae. Diameter of amphideal fovea about 9 µm, (i.e. 70% of corresponding body diameter). Pharynx cylindrical, posteriorly gradually enlarging, but not forming a true posterior bulb. Cardia well developed. Nerve ring just before the middle of the pharynx length. Secretory-excretory system consisting of unicellular gland located at level with anterior part of intestine; secretory–excretory duct with distinct ampulla and opening just posterior to the nerve ring. Tail conico–cylindrical, general more than 6 anal body diameters long, with an evident spinneret; two terminal setae, 7–10 µm long.

Reproductive system diorchic. Testes opposed and outstretched with visible spermatozoa irregularly oviform in shape. Anterior testis situated to the left of intestine, posterior testis situated to the right of intestine. Spicules slender and elongated with thick cuticularized proximal end, equal on average to 4.6 corresponding body diameter at the cloaca level. Gubernaculum plate-like without apophysis, about 20 µm long. Precloacal ventral cuticle thickened. One short (i.e. 3 µm long) precloacal seta located just before the cloaca. Thirty to thirty nine minute tubular precloacal supplements present.

Female. Similar to males in most characters except body slightly longer, cephalic setae slightly longer and amphids with 2.5 turns. Reproductive system didelphic, two ovaries opposed and outstretched. Anterior ovary situated to the left of intestine, posterior ovary situated to the right of intestine. Oviduct a wide tube with oblong eggs. Two oval, sac-like spermathecae located on each side of each (anterior and posterior) gonoduct, filled with oval spermatozoa. Uterus a short tube. Vagina straight. Vulva located just before the midbody (i.e. at 44–46% of total length), opening by a small pore and with slightly raised lips.

Differential diagnosis and discussion. Paracomesoma zhangi is characterized by cuticle with fine transverse rows of dots, without lateral differentiation; buccal cavity with three small teeth; cephalic setae thick and more than twice the length of the outer labial setae; multispiral amphideal fovea with 2.5–3 turns; spicules slender and elongated with thick cuticularized proximal end; gubernaculum plate-like without apophysis; 26–39 minute precloacal supplements. These specimens from the South China Sea are in full agreement with our original description from the East China Sea except having more precloacal supplements (more than 30 vs 26 in holotype), males slightly smaller (not longer than 1710 µm vs 1868 µm in holotype) and with shorter cephalic setae (not longer than 10 µm vs 13.5 µm in holotype). Paracomesoma zhangi is rare species in the East China Sea and it is common species in the Qiongzhou strait of the South China Sea.

Figures

FIGURE 3. Paracomesoma zhangi Huang & Huang, 2018. (A) lateral view of female head end, showing buccal cavity, cephalic setae and amphid; (B) lateral view of male anterior end, showing pharynx and secretory-excretory system (C) lateral view of male posterior end, showing spicule, gubernaculum, precloacal supplements and tail; (D) entire view of female, showing vulva, ovary and eggs.

FIGURE 4. Paracomesoma zhangi Huang & Huang, 2018. (A) lateral view of female anterior end; (B) lateral view of male anterior end; (C) lateral view of male cloacal region, showing spicule; (D) lateral view of male cloacal region, showing spicule, gubernaculum and precloacal supplements. (Scales: A, B 10 µm; C, D 20 µm)