Cyartonema breviseta Wen & Huixin & Mengna & Chunming 2023, sp. nov.

Cyartonema breviseta sp. nov.

(Figures 3–4, Table 1)

Type material. Three males and two females were measured and studied. Holotype: ♂ 1 on slide 21YMD2-2-6, paratypes: ♂2 on slide 21YMD2-2-39, ♂3 on slide 21YMD2-2-142, ♀ 1 on slide 21YMD2-2-229, and ♀2 on slide 21YMD2-2-248.

Type locality and habitat. Specimens were collected from intertidal muddy sediment at Yangma Island, Shandong Province; 37º28´N, 121º38΄E; 0–2 cm sediment depth.

Etymology. Species epithet breviseta refers to the short cephalic setae.

Description. Males. Body short and slender. Anterior body end narrowed. Inner and outer labial sensilla not visible. Four cephalic sensilla short and papilliform, 1.5 μm in length. Cuticle faintly annulated. Amphideal fovea circular and large (60%–71% c.b.d.), 6–8 μm from anterior body end. Buccal cavity absent. Pharynx divided into three sections, anterior part muscular (35–45μm long), middle part narrow (20–22 μm long) and posterior part widened with triangular bulb (19–21 μm long), nucleated cells of pharyngeal gland present at the pharynx bulb, and pharyngeal gland canal unclear. Cardia present and heart-shaped. Nerve ring situated 48–56 μm from anterior end. Excretory cell observed. Pseudolococyte present, intestine end blind, rectum and anus absent. Tail conical, 4.7–5.4 cloacal body diameter, three caudal glands present and in line. Spinneret short.

Testis paired, both located to the left of the intestine. Spicules paired, curved, sickle-shaped, 1.6–1.9 cloacal body diameter. Gubernaculum highly cuticularized with dorso-caudal apophysis, posterior end hooked anteriorly.

Females. Similar to males in most characters. Reproductive system didelphic and amphidelphic, with reflexed ovaries. Anterior ovary to the left of the intestine, posterior to the right. Vulva located anterior to the mid-body, 373–410 μm from anterior end. Vagina short and sclerotized.

Differentiation diagnosis and discussion. Cyartonema breviseta sp. nov. can be differentiated by a relatively short and slender body, amphideal fovea circular, four cephalic setae short and papilliform, spicules curved and sickle-shaped, gubernaculum with dorso-caudal apophysis and posterior end hooked anteriorly, tail conical.

Cyartonema breviseta sp. nov. differs from the other species of Cyartonema with the character of gubernaculums. It is similar to C. minor, C. parvulum, and C. zosterae in the short cephalic setae and conical tail, but differs from C. minor in the longer body (737–846 μm vs. 487–538 μm), amphideal fovea position (6–8 μm from anterior body end vs. 3.0–4.2 μm from anterior body end), spicules shape (sickle-shaped vs. strongly curved), and gubernaculum shape (with dorso-caudal apophysis, posterior end hooked vs. with dorso-caudal apophysis, posterior end straight); from C. parvulum in spicules length and shape (27–32 μm, sickle-shaped vs. 22.5–25.5 μm, proximal end widened toward the ventral), precloacal supplements absent (one papillate precloacal supplement present in C. parvulum); from C. zosterae in cephalic setae length (1.5 μm vs. 6.7–8.4 μm), spicules shape (sickle-shaped vs. distally pointed, curved in the proximal part and obliquely rounded), and tail length (5 cloacal body diameter vs. 2.1 cloacal body diameter) (Tchesunov 1989).