Halichoanolaimus sinensis, Huang & Zhai, 2024

Huang, Mian & Zhai, Hongxiu, 2024, Two new species of the genus Halichoanolaimus (Nematoda, Selachinematidae) from the intertidal zone of the Yellow Sea, China, ZooKeys 1208, pp. 259-274 : 259-274

Halichoanolaimus sinensis sp. nov.

Figs 1 , 2 , Table 1

Material examined.

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.

Type locality and habitat.

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.

Etymology.

The specific epithet refers to the country origin, China.

Measurements.

All measurement data are given in Table 1 .

Description.

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. 2 C ). Amphideal fovea multispiral with 3 turns (Fig. 2 B ), 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.

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. 2 E ), 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.

Differential diagnosis and discussion.

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

Figures

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).