Thalassironus filiformis, Huang & Huang & Xu, 2019

Huang, Mian, Huang, Yong & Xu, Kuidong, 2019, Thalassironus filiformis sp. nov. (Nematoda, Enoplida) from the South China Sea, Zootaxa 4657 (1), pp. 170-176 : 171-174

Thalassironus filiformis sp. nov.

( Figs 1–2 )

Type material. Two males, two females and a juvenile specimens were collected from Station nh17- 3 in the Qiongzhou Strait of the South China Sea by Dr. Mian Huang in February 2017 . Type specimens were deposited in the Marine Biological Museum of Chinese Academy of Sciences, Qingdao . Male holotype on slide MBM286550 nh17-3(2-5)-46-1 ; one male, one female and one juvenile paratypes on slide MBM286551 nh17-3(2-5)-130-11 ; anothor female paratype on slide MBM286552 nh17-3(2-5)-46-1.

Type locality and habitat. Subtidal silt sediment at Station nh17-3 with water depth of 16 m in the Qiongzhou Strait (20°3′53″ N; 110°21′5″ E). All specimens were found in the 2–5 cm sediment depth layer.

Etymology. The species name refers to its long filiform tail.

Measurements. Table 1

Description. Males. Body slender, elongate spindle-shaped, 3680–3700 μm long, width at midbody 56 μm. Cuticle thick and smooth. Head slightly set-off. Inner labial sensilla papilliform, six outer labial setae and four cephalic setae in one circle and almost equal in length, 8 μm long. Amphideal fovea pocket-like, about 8 μm wide and located poster to cephalic setae, 20 μm from the anterior end. Double cervical setae not observed. Buccal cavity cy- lindrical, 46–47 μm long and 5 μm wide, with sclerotized walls and three prominent teeth at anterior end.Additional three teeth located just posterior to amphideal fovea. Pharynx beginning at the level of the base of teeth, peribuccal portion expanded, forming an anterior pharyngeal bulb, then a narrow section to nerve ring, increasing gradually in diameter between nerve ring and the base of pharynx, not forming posterior pharyngeal bulb. Excretory pore not observed. Tail very long, 772–780 μm, i.e. 21 times as long as cloacal body diameter, conical, tapering gradually to filiform tip. Three caudal glands present in the conical region of tail. Spinneret not distinct.

Reproductive system monorchic with an outstretched testis. Spicules slender, slightly double curved ventrally with a median cuticularized septum in the anterior portion and with an ala in the middle and posterior portion, 68 μm long. Gubernaculum 22 μm, rod-like, slightly curved, without apophysis. Single large segmented midventral precloacal seta present in front of the cloaca.

Females. Similar to males, but body length slightly shorter. Reproductive system didelphic, two ovaries opposed and reflexed, situated ventrally. Anterior ovary situated to the left of intestine, posterior ovary situated to the right of intestine. Uterus broad. Vagina short and straight. Vulva located anteriorly to the middle of the body.

Juvenile. Similar to males and females in most morphological characters except for smaller morphological measurements.

Figures

FIGURE 1. Thalassironus filiformis sp. nov. (A, B, D, holotype) (A) lateral view of male head end, showing cephalic setae, teeth, buccal cavity and amphideal fovea; (B) lateral view of male posterior end; (C) entire view of female, showing vulva, uterus and ovaries; (D) lateral view of male cloaca region, showing spicule, gubernaculum and precloacal seta; (E) lateral view of female anterior end; (F) female reproductive system, showing vulva, vagina and ovary.

FIGURE 2. Thalassironus filiformis sp. nov. (A–D, holotype) (A) lateral view of male anterior end, showing teeth; (B) lateral view of male anterior end, showing buccal cavity and cephalic setae; (C) lateral view of male cloacal region, showing spicule; (D) lateral view of male cloacal region, showing gubernaculum and precloacal seta. (Scales: A, B, C, D 20 μm)