Paramonohystera gracilis, Zhai & Geng & Sun, 2022

Zhai, Hongxiu, Geng, Chunxiao & Sun, Jun, 2022, Two new species of Xyalidae (Nematoda: Monhysterida) from intertidal zone of the Bohai Sea, China, Zootaxa 5222 (2), pp. 133-144 : 135-138

Paramonohystera gracilis sp. nov.

( Figs. 1–2 ; Table 1 )

Type material. Three males and two females were collected. Holotype on the slide 2021-XC2-5-15 ; Paratypes: male 2 on the slide 2021-XC2-5-24, male 3 on the slide 2021-XC2-5-19, female 1 on the slide 2021-XC1-2-19, female 2 on the slide 2021-XC3-2-23 and female 3 on the slide 2021-XC1-2-13.

Type locality and habitat. Intertidal sandy sediment at Xingcheng along the Bohai Sea (40°37′30″ N, 120°48′7″ E).

Etymology. The species name is derived from the Latin gracilis , referring to its thin and slender body.

Measurements. Table 1 .

Description. Holotype. Body slender with a very long tail. Cuticle with fine striations. Buccal cavity large with hemispherical cheilostome and conical pharyngostom. Anterior sensilla arranged in two circles. Six inner labial sensilla papilliform; six outer labial sensilla setiform, 6 μm long and with four cephalic setae arranged in one same circle. Additional two cephalic setae located just posterior to the circle of outer labial setae. A circle of four cervical setae located posterior to amphids. Amphideal fovea circular, 6 µm in diameter or 50% of corresponding body diameter. Anterior border of fovea located posterior to buccal cavity, i.e. 12 µm from the head end. Pharynx cylindrical with enlarged base, about 10% of total body length. Pharyngo-intestinal junction with a large conical cardia, and surrounded by the intestine. Nerve ring at just before the mid of pharynx, about 67% of pharyngeal length from the anterior end. Excretory pore and ventral gland not seen. Tail long and slender, distal three quarters filiform. Tail tip slightly swollen with three 9 µm long terminal setae and a pointed spinneret. Three caudal gland cells arranging in tandem. Three caudal setae distributing on the conical region of tail. Reproductive system diorchic, testes opposite and outstretched.Anterior testis to the left of intestine, posterior one to the right of intestine. Spicules slender and elongate, 3.4 cloacal body diameter in length, bended ventrally at distal third part, slightly cephalated proximally and tapered distally. Gubernaculum plate shaped, without apophysis, dorsal to spicules. No precloacal supplements observed.

Females. Similar to males in most morphological characteristics, but slightly larger body with longer tail and smaller amphidial fovea. A single long anterior outstretched ovary stretching to the pharyngeal base, situated to the left of the intestine. Ovary a wide tube, filled with oocytes. Uterus a short tube. Vagina straight. Spermatheca present. Vulva at the rear part of the body, about 70% of the body length from the anterior end.

Differential diagnosis and discussion. Paramonohystera gracilis sp. nov. is characterized by a slender body with a long filiform tail; circular amphidial fovea 5–7 µm in diameter; spicules slender, 3.4 cloacal body diameter; gubernaculum small, plate shaped without apophysis, tail 14–18 times as long as cloacal or anal body diameter.

So far, 16 valid species have been recorded for the genus. The new species can be easily recognized from other congeners by its slender body and distinctively long filiform tail (c′>14 vs c′<12). Among them, the present species is most close to P. riemanni in both having similar body size and general morphology, but it differs from the latter species by males having much slender body (a = 65.5–71.5 vs 52–60) and longer filiform tail (c′=14.4–15.4 vs 7–11). In P. riemanni , spicules present dilation distally, whereas the new species has no the character. Timm (1963) ever described a species, Paramonohystera longicaudata , which has a long filiform tail (c′=10). Nevertheless, the spicules of P. longicaudata are not elongated, only 26–28 µm, i.e. 1.5 times as long as cloacal body diameter. It should not belong to the genus. Paramonohystera longicaudata has been considered as an uncertain species of the genus ( Yu & Xu, 2015). The difference between P. gracilis sp. nov. and its congeners can be inferred from the key below.

Figures

FIGURE 1. Paramonohystera gracilis sp. nov. (A) anterior region of male; (B) posterior region of male; (C) entire view of female; (D) anterior end of male; (E) spicules and gubernaculum. Scale bars: A, B 20 µm; C 50 µm, D, E 10 µm.

FIGURE 2. Paramonohystera gracilis sp. nov. (A) anterior region of male, showing buccal cavity; (B) anterior region of male, showing amphid and anterior setae; (C) posterior region of male; (D) cloacal region of male, showing spicules and gubernaculum. Scale bars: A, B, D 10 µm; C 30 µm.