Halomonhystera zhangi, Li & Huang & Huang, 2024

Li, Ting, Huang, Yong & Huang, Mian, 2024, Two new species of the order Monhysterida (Nematoda) from the sea of China, ZooKeys 1193, pp. 63-79 : 63

Halomonhystera zhangi sp. nov.

Figs 1 , 2 , 3

Diagnosis.

Halomonhystera zhangi sp. nov. is characterized by relatively small body size, anterior sensory setae 3 µm long; small circular amphidial fovea located at the level of buccal cavity base; buccal cavity funnel-shaped; excretory-secretory system with large ventral gland and opening close to the level of cephalic setae by a very thin canal; slender spicules curved slightly with cephalated proximal end and tapered distal end; gubernaculum rod-like, without apophysis; two papilliform precloacal supplements just in front of cloaca; tail conico-cylindrical with two ventral papillae and each with a seta; testis outstretched with folded anterior portion, situated at the right side of the intestine; distance between the vulva and anus longer than the tail length.

Material examined.

Four males and two females were obtained. Holotype: ♂ #1 on slide QDZQ-16JL-89; paratypes: ♂ #2 on slide QDZQ-11SC-148, ♂ #3 on slide QDZQ-11SC-157, ♂ #4 on slide QDZQ-16JL-93, ♀ #1 on slide QDZQ-16JL-97, and ♀ #2 on slide QDZQ-16JL-98. Type specimens were deposited in the Marine Biological Museum of the Chinese Academy of Sciences, Qingdao.

Type locality and habitat.

Holotype and all the additional specimens were found from Sargassum thunbergii (seaweed) growing on the intertidal rocky reef of Qingdao Trestle, China (36°37.43′N, 120°18.9′E).

Etymology.

The specific epithet “zhangi” is in honor of Professor Zhinan Zhang, a Chinese nematologist, in recognition of his contributions to nematode taxonomy.

Measurements.

All measurement data are given in Table 1 .

Description.

Males. Body slender, tapering towards both extremities. Cuticle smooth without transversely striated. Four longitudinal rows of short somatic setae sparsely distributed throughout the body, 3-4 µm long. Head diameter representing 39-42% of the maximum body diameter. Inner labial sensilla papilliform. Outer labial sensilla setiform. Outer labial setae and cephalic setae united in one circle with a total of 12 setae, each 3 µm long, i.e. 27-30% of head diameter, situated at the level of middle of the buccal cavity. Amphidial fovea circular with a diameter of 4 µm, which is occupying 29-31% of the corresponding body diameter, located at the level of buccal cavity base, i.e.7-8 µm from the anterior end. Buccal cavity funnel-shaped, without teeth. Pharynx cylindrical with a swollen base, not forming a real terminal bulb. Cardia conical, 6-9 µm long. Nerve ring situated posterior to the middle of pharynx. Excretory-secretory system with a large ventral cell, situated near anterior section of intestine; ampulla situated posterior to amphidial fovea, about 25 µm from the anterior end of body; a very thin canal extended forwards from the ampulla, and opening just posterior to the level of outer labial and cephalic setae crown. Tail conical with posterior third cylindrical, equal to 4.4-4.8 cloacal body diameter long. Tail tip slightly swollen with a conical hyaline spinneret (Fig. 2D ). Terminal setae absent. A few short caudal setae sparsely distributed throughout the tail. Two prominent caudal gland cells confined entirely to the tail.

Reproductive system monorchic with an outstretched testis with folded anterior portion, situated at the right side of the intestine. (Fig. 2F ). Spicules slender, arcuated, proximally cephalated and distally pointed, 1.52-1.96 times of cloacal body diameter. Gubernaculum rod-like, slightly curved proximally, without apophysis. Two papilliform precloacal supplements, one just anterior to cloaca, another one 30-50 µm anterior to cloaca. Two ventral caudal papillae in the middle region of tail, each with a short seta. The anterior one located at 43-52 µm posterior from cloaca, and the other at 63-72 µm posterior from cloaca.

Females. Similar to males in most morphological characteristics except cephalic setae slightly longer and amphidial fovea relatively smaller. Reproductive system monodelphic with an anterior outstretched ovary, located at the right side of intestine. Mature egg large, oval. Uterus a wide tube. Vulva located posterior to mid-body (i.e. 57.9-58.3% of body length from the anterior end). Distance between the vulva and anus (155-183 µm) longer than the tail length (107-122 µm). Spermatheca not seen.

Differential diagnosis and discussion.

Halomonhystera zhangi sp. nov. agrees well with the primary diagnostic characters of the genus, especially in having well developed excretory-secretory system with large ventral gland and opening at anterior pharyngeal region, spinneret with hyaline structure, males having papillary precloacal supplements and caudal papillae. The inconsistent characters to diagnosis of Halomonhystera are cephalic setae paired and vulva not very close to anus.

The present species is similar to H. chitwoodi (Steiner, 1958) Andrássy, 2006 in the position of amphidial fovea (closing to anterior end of body), the distance between vulva and anus (not shorter than the tail length) and they all growing on Sargassum , but it differs from the latter species by slightly smaller body size (vs longer than 1 mm), two papilliform precloacal supplements (vs only one precloacal supplement), and conico-cylindrical tail with two ventral bristled papillae (vs conical tail without bristled papilla). In having relatively long distance between the vulva and anus, the new species resembles H. glaciei (Blome & Riemann, 1999) Andrássy, 2006, but differs from it by the much shorter and stouter body (vs 2 mm or more, a = 60 or more), the amphidial fovea closing to the anterior body end (vs two labial diameters from anterior end) and by the shorter tail (vs c′= 7). The new species can easily be distinguished from other known species within this genus by relatively small body size, position of amphidial fovea near to anterior end of body, two papilliform precloacal supplements, conico-cylindrical tail with two ventral bristled papillae. The difference between H. zhangi sp. nov. and other known species within the genus can be inferred from the key below.

Figures

Figure 1. Drawings of Halomonhystera zhangi sp. nov. A anterior end of male B anterior end of female C entire body of female D posterior end of male E spicules and gubernaculum F entire body of male. Scale bars: 10 μm (A, B); 30 μm (C, F); 20 μm (D, E).

Figure 2. Microscopic images of Halomonhystera zhangi sp. nov. A anterior end of holotype, showing anterior setae, renette ampulla (arrow) B, C anterior end of holotype, showing buccal cavity, cephalic setae, excretory pore (arrow 1) and amphidial fovea (arrow 2) D posterior end of holotype, showing gubernaculum and caudal papillae (arrows) E cloacal region of paratype 1, showing spicule and precloacal papillae (arrows) F anterior portion of testis of holotype. Scale bars: 10 μm (A - E); 20 μm (F).

Figure 3. Microscopic images of Halomonhystera zhangi sp. nov. A anterior end of female 1, showing buccal cavity and anterior setae B anterior end of female 2, showing cephalic setae and amphidial fovea (arrow) C middle region of female, showing ovary (arrow 1), egg (arrow 2), vulva (arrow 3), anus (arrow 4) and caudal glands (arrow 5) D anterior region of female intestine, showing pharyngeal base (arrow 1), ventral gland (arrow 2) and ovary (arrow 3). Scale bars: 10 μm (A, B); 30 μm (C, D).