Dichromadora simplex Timm, 1961

Gagarin, Vladimir G., 2020, Microlaimus capitatus sp. n. and Dichromadora simplex Timm, 1961 (Nematoda, Chromadorea) from the coast of Vietnam, Zootaxa 4732 (2), pp. 323-331 : 328-331

Dichromadora simplex Timm, 1961

( Figs 3 , 4 ; Table 2 )

Studied material. 8 males and 4 females, slide deposited in the nematode collection of the Department of Nematology , Institute of Ecology and Biological Resources (Hanoi, Vietnam) .

Locality. South China Sea, littoral zone of coastal Vietnam. Latitude: 21º26ʹ13ʹʹ– 21º26ʹ86ʹʹ. Longitude: 107º45ʹ24ʹʹ–107º45ʹ61ʹʹ. Depth 0.5–3.0 m, mangroves, sand, salinity 13–14‰. Collected on June 2016.

Description. Males. Body comparatively short and slender. Cuticle finely annulated, marked with transverse rows of fine punctations. Lateral fields consisting of two longitudinal rows of large points and 3–4 µm wide. Cuticle approximately 1 µm thick at mid-body. Somatic setae few, short. Anterior edge of head slightly truncated. Lips well developed. Labial sensillae in the shape of small papillae. Four cephalic sensillae in the shape of thin setae approximately 3 µm long, 25–30% of labial region diameter. Cheilostom strengthened by sclerotized ribs. Pharyngostom “funnel”-shaped and armed with a large dorsal tooth and two smaller subventral teeth. Total length of stoma 5–6 µm. Amphidial fovea oval, transversely stretched, situated at base of lips. Pharynx comparatively short, muscular, with a well-developed cardiac bulb having thick inner cuticular lining. Cardia small. Renette saccate, stretched longitudinally and situated at the beginning of the intestine. Excretory pore posterior to nerve ring.

Testis single, straight, situated to right side of intestine. Spicules slender, curved, cephalated, 1.2–1.4 times as long as cloacal body diameter. Gubernaculum in the shape of a “boat”, 12–17 µm long. Precloacal supplements absent. Tail elongate-conical, curved ventrally. Caudal glands well developed. Spinneret bearlike.

Females. General appearance similar to that of males. Structure of cuticle and anterior portion of body similar to males. Cuticle faintly annulated. Lateral fields consisting of two longitudinal rows of large points. Somatic setae short and sparse. Labial sensillae in the shape of papillae. Four cephalic setae thin setae 2–3 µm long. Cheilostom with longitudinal cuticularized ribs. Pharyngostom funnel-shaped and armed with a larger dorsal tooth and two smaller subventral teeth. Pharynx muscular, its cardiac bulb large, elongate-spherical, with large inner cavity. Renette situated at the pharyngo-intestinal junction. Excretory pore located posterior to nerve ring.

Reproductive system didelphic, amphidelphic; ovaries antidromous. Anterior ovary situated to right side of intestine, posterior ovary to left side. Vulva a transverse slit, preequatorial. Vulval lips neither cuticularized nor protruding outside the body contour. Vagina relatively short with thick walls. Uterus rather spacious, filled with numerous spermatozoids. Spermatheca and vulval glands not observed. Tail elongate-conical, slender. Caudal glands and spinneret well developed.

Discussion. Dichromadora simplex Timm, 1961 was described based on 4 males from the Bay of Bengal ( Timm 1961). Subsequently this species has been found associated with mangroves in Vietnam ( Gagarin 2018).

Males from the South China Sea littoral are morphologically close to the males from the Bay of Bengal, with one exception: the gubernaculum is somewhat longer (12–17 µm long vs 10 in the original description). Females are described and illustrated for the first time.

Figures

FIGURE 3. Dichromadora simplex Timm, 1961. A: male head; B: male, anterior body end; C: male tail; D: female, vulva region; E: female tail. Scale bars: A—10 µm; D—20 µm; C—25 µm; E—30 µm; B—40 µm

FIGURE 4. Dichromadora simplex Timm, 1961. A: male, entire body; B: female, entire body; C: male, anterior body end; D: male head; E: female head; F: female, vulva region; G: male, cloaca region; H: male head; I: female tail; J: male, tail terminus. Scale bars: A, B—50 µm; C, F, H, I—10; D, E, G, J—5 µm