(modified from Leduc 2020). Cuticle with lateral differentiation in the form of larger and more widely spaced punctations. All anterior sensilla usually papilliform. Buccal cavity separated into two chambers by transversal sets of denticles; posterior chamber of buccal cavity surrounded by three Y-shaped pairs of cuticularized rhabdions. Pharynx without anterior or posterior bulb. Intestine of adult stages blind. Precloacal supplements usually papilliform or setiform. Tail with conical proximal portion and often elongated cylindrical distal portion.

Four males and two females were obtained. Holotype: ♂1 on slide RZ08-7-5; paratypes: ♂2 on slide RZ08-7-2, ♂3 on slide RZ08-7-5, ♂4 and ♀1 on slide RZ08-7-3, and ♀2 on slide RZ08-7-2. Type specimens were deposited in the Marine Biological Museum of the Chinese Academy of Sciences, Qingdao.

Holotype and all additional specimens were found from intertidal silt sediment at Rizhao coast of the Yellow Sea; 35°26'N, 119°34'E; 0–2 cm and 2–5 cm sediment depth.

The specific epithet refers to the country origin, China.

All measurement data are given in Table 1.

Males. Body cylindrical, tapering slightly towards posterior end. Cuticle with transverse rows of punctations, lateral differentiation consisting of slightly larger and more widely spaced punctations. Cuticle pore not observed. Somatic setae short, 3 µm long, sparsely distributed. Lip region slightly rounded. Six inner labial sensilla papillose; six outer labial sensilla setiform, 3–4 µm long, at same level as four papilliform cephalic sensilla (Fig. 2C). Amphideal fovea multispiral with 3 turns (Fig. 2B), 25–27% of corresponding body diameter in width, located at the level of the middle of buccal cavity, ca 20 µm from anterior end of body. Buccal cavity large, ca 45 µm deep, divided into anterior and posterior portions by two rows of 15–17 denticles. Anterior portion of buccal cavity cup-shaped, with three sets of three cuticularized rhabdions; posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularized rhabdions with swollen bases, 20 µm long. Pharynx cylindrical, anterior end swelling, wrapped the buccal cavity, without posterior bulb. Pharyngeal lumen cuticularized. Nerve ring at ca 44% of pharynx length from anterior end. Secretory-excretory system present. Renette cell small, situated at level of cardia; ampulla large, excretory pore situated slightly posterior to the nerve ring, ca 180 µm from the anterior end. Cardia small, surrounded by intestine.

Figure 1. 

Drawings of Halichoanolaimus sinensis sp. nov. A pharyngeal region of male B posterior end of male C entire body of female D entire body of male E anterior end of male. Scale bars: 30 μm (A, B, E); 100 μm (C, D).

Figure 2. 

Microscopic images of Halichoanolaimus sinensis sp. nov. A anterior end of holotype, showing buccal cavity and excretory ampulla (arrow) B anterior end of male 2, showing amphidial fovea C anterior end of holotype, showing stomatorhabdions and anterior sensilla (arrow) D posterior part of holotype, showing supplements E cloacal region, showing spicules, gubernaculum and supplements. Scale bars: 20 μm (A, B, C, E); 30 μm (D).

Reproductive system diorchic with two opposed, outstretched testes. Anterior testis to the right or ventrally to intestine, posterior testis to the left side of intestine. Spicules paired, curved, middle portion broad, tapering distally, 1.4–1.5 cloacal body diameters long, interior of spicules granular in appearance. Gubernaculum slender, consisting of two detached lateral pieces tapering distally, adjoining the dorsal side of spicules. 10–13 papilliform precloacal supplements in two groups, the posterior three supplements smaller and closer to each other (Fig. 2E), located 7 µm from the cloaca; 5 µm from each other; remaining supplements larger and widely spaced, ca 25 µm from each other. Each supplement consisting of conical papilla and an internal duct. Tail conico-cylindrical with posterior cylindrical portion comprising about half of total tail length. Caudal setae absent. Three caudal glands located posterior to spicules, spinneret present, 7 µm long.

Females. Similar to males, but with slightly larger body and slightly smaller amphideal fovea (20% of corresponding body diameter in width and with 2.5 turns). Reproductive system didelphic, with two opposed, reflexed ovaries. Anterior ovary to the left of intestine and posterior ovary to the right of intestine. Vulva situated slightly pre-median. Intestine blind, anus not observed.

Halichoanolaimus sinensis sp. nov. is characterized by amphideal fovea with 2.5–3.0 turns, 20–27% of corresponding body diameter; spicules curved, middle portion broad, tapering distally, 1.4–1.5 cloacal body diameters long; gubernaculum slender consisting of two detached lateral pieces tapering distally; 10–13 papilliform precloacal supplements in two groups, the posterior three supplements smaller and closer to each other, remaining supplements larger and widely spaced; tail conico-cylindrical with half cylindrical portion. The new species is most similar to H. sonorus Belogurov & Fadeeva, 1980 in body shape and number of precloacal supplements, but differs from the latter species by numbers of amphid turns (2.5–3 vs 4–4.2), different shape and structure of spicules (spicules without capitulum, distal hook and central spacer vs with weak capitulum, distal hook and central spacer). The new species is also similar to H. stagnalis Gagarin & Long, 2017 in the number of the amphidial turns and tail, but can easily be distinguished from the latter by the different arrangement of precloacal supplements (3 posterior supplements smaller and closer vs 5–6 smaller and closer supplements

Two males and one juvenile were obtained. Holotype: ♂1 on slide 22HSB-11-2-1; paratypes: ♂2 and juvenile on slide 22HSB-11-2-2. Type specimens were deposited in the Marine Biological Museum of the Chinese Academy of Sciences, Qingdao.

Holotype and paratypes were found from intertidal muddy sediment at Rizhao coast along the Yellow Sea; 35°18'N, 119°31'E; 0–2 cm sediment depth.

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

All measurement data are given in Table 2.

Males. Body cylindrical, tapering slightly towards posterior end. Cuticle with transverse rows of punctations. Lateral differentiation presents except to anterior half of pharynx with even punctations. Lateral differentiation consisting of slightly larger and more widely spaced punctations. Four longitudinal rows of pore complexes situated at sublateral sides of pharyngeal region (Fig. 4B). Each row with 10–12 pores. Cephalic region slightly rounded. Inner and outer labial sensilla papillose; four cephalic sensilla setiform, 4–5 µm long. Amphideal fovea multispiral with 3–3.25 turns, located at the level of the buccal cavity base, 27–28 µm from anterior end of body. Buccal cavity large, 43–45 µm deep, divided into anterior and posterior portions by two rows of 25 denticles. Anterior portion of buccal cavity cup-shaped, with three sets of three cuticularized rhabdions, terminating in three sets of paired denticles; posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularized rhabdions with swollen bases, ca 20 µm long. Pharynx cylindrical, muscular, without anterior or posterior bulb; pharyngeal lumen cuticularized. Nerve ring difficult to distinguish. Secretory-excretory system present. Ventral gland small, situated at level of cardia; ampulla large, excretory pore situated at position of three corresponding body diameters from the anterior end. Cardia small, partially surrounded by intestine.

Figure 3. 

Drawings of Halichoanolaimus zhangi sp. nov. A pharyngeal region of holotype B anterior end of holotype C cloacal region of holotype D posterior end of male 2. Scale bars: 30 μm (A, B, C); 50 μm (D).

Figure 4. 

Microscopic images of Halichoanolaimus zhangi sp. nov. A anterior end of holotype, showing buccal cavity and excretory pore (arrow) B anterior end of holotype, showing cephalic seta (arrow 1) amphidial fovea and cuticle pores (arrow 2) C posterior portion of male 2, showing spicules and tail D cloacal region of holotype, showing spicules, gubernaculum and supplements. Scale bars: 20 μm (A, B, D); 50 μm (C).

Reproductive system diorchic with two opposed, outstretched testes. Anterior testis to the right or ventrally to intestine, posterior testis to the left side of intestine. Spicules paired, curved, gradually narrowing from proximal to distal end with pointed tip, ca 2 cloacal body diameters long. Gubernaculum rod-like, adjoining to the dorsal side of spicules. 7 papilliform precloacal supplements, the most posterior supplement located 14 µm from the cloaca; remaining supplements gradually increasing the spacing distance forward, from 9 µm to 26 µm to each other. Each supplement consists of conical papilla and an internal duct. Two rows of short conical setae situated at two subventral sides of the precloacal supplements region of body. Tail conical with a long posterior filiform portion, accounts for 92% total tail length. A row of 5 caudal setae distributed at ventral side of tail conical part, 3–4 µm long. Caudal glands and spinneret present, 7 µm long.

Figure 5. 

Microscopic images of Halichoanolaimus zhangi sp. nov. A anterior end of holotype, showing lateral differentiation and somatic setae (arrow) B cloacal region of holotype, showing lateral differentiation and conical setae situated at two subventral sides of precloacal supplements (arrow) C anterior end of juvenile, showing buccal cavity and cephalic sensilla (arrow) D posterior portion of juvenile, showing the end of intestine (arrow). Scale bars: 20 μm (A, B, C, D).

Female not found. Juvenile similar to males in body shape, and with a long filiform tail, except body size smaller, intestine with blind end.

Halichoanolaimus zhangi sp. nov. is distinct by lateral differentiation presenting posterior to the middle of the pharynx, amphideal fovea with 3.0–3.3 turns, spicules curved, gradually narrowing from proximal to distal end with pointed tip, 7 papilliform precloacal supplements, gradually increasing the spacing distance forward, two rows of subventral stout setae situated at precloacal region, tail elongated, filiform. The new species is most similar to H. possjetiensis Belogurov & Fadeeva, 1980 in the filiform tail and number of precloacal supplements, but differs from the latter species by body slender (a=38.6–38.9 vs body stout, a=25.8–26.6), longer tail (c=4.9–5.2 vs c=8–8.3) and different gubernaculum (slender and straight vs. broad and hooked proximally in H. possjetiensis).