Eleutherolaimus sinensis Huang, Sun and Bai, 2025

Eleutherolaimus sinensis Huang, Sun and Bai sp. n.

( Figures 3–5 View Figure 3 View Figure 4 View Figure 5 and Table 1)

Holotype and paratype material

Three males and one female were obtained and measured. Holotype (male 1) and paratypes (male 2, male 3 and female 1) are all on slide RZ0807x-1.

Type locality and habitat

Holotype and paratype were all collected from the surface layer of fine sand sediment on an intertidal beach along the Rizhao coast of the Yellow Sea, China ( 35°34′21″N, 119°39′ 29″E) in 2008 GoogleMaps .

Etymology

The specific epithet refers to the country origin, China.

Measurements

All measurement data are given in Table 1.

cephalic setae and amphidial fovea; (c) anterior end, showing buccal cavity and subcephalic setae; (d) posterior portion, showing spicule, gubernaculum and tail; (e) right spicule and gubernaculum of male 2; (f) left spicule of male 2. Scale bars: a, d = 20 µm; b, c, e, f = 10 µm.

Description

Males. Body slender, cylindrical, tapering slightly towards both extremities. Cuticle finely striated, no lateral differentiation. Short somatic setae largely absent except in pharyngeal and cloacal regions, sparsely distributed, 3–4 µm long. Head truncated and not offset from the body. Minute labial papillae barely discernible around the mouth opening. Two separate circles of equilong cephalic and subcephalic setae located on lip region, each circle consisting of 4 setae, 3.5–4 µm long. Amphidial fovea circular, outline slightly cuticularised, at level of junction of buccal cavity and pharynx, 4 µm wide, or 40% corresponding body diameter. Buccal cavity cylindrical, 4 µm wide, 7–8 µm deep, with cuticularised walls and cuticularised ring. Pharynx muscular, widening slightly posteriorly but not forming true bulb. Nerve ring located slightly posterior to mid-pharynx. Secretory-excretory system with a large ventral gland situated at the anterior portion of intestine; excretory pore located anterior to nerve ring, about 110 µm from the anterior end of body. Cardia conspicuous, partially surrounded by intestine, 13–14 µm long.

Reproductive system with two opposed testes; position of testes relative to intestine unclear. Spicules 1.1–1.2 cloacal body diameters long, cuticularised, ventrally arcuate; cephalate proximal end and with short central lamella one-third of spicule length from distal tip. Gubernaculum triangular, with straight cuticularised dorsocaudal apophyses. Precloacal supplements not observed. Tail sub-cylindrical with bluntly rounded tip; two rows of 9–10 pairs of subventral setae 3–4 µm long, and two pairs of subdorsal setae near tail tip. Three caudal gland cells located mostly in anterior half of tail; spinneret present.

Female. Similar to males except tail slightly shorter and without caudal setae, and caudal gland cells extending anteriorly slightly beyond the anus. Reproductive system with two opposed outstretched ovaries; anterior ovary to the left of intestine, extending forward to 490 µm from the head end; posterior ovary to the right of intestine, extending back to 20 µm from the level of anus. Spermatheca not observed. Vulva protruding outward, situated posterior to mid-body.

Species diagnosis. Eleutherolaimus sinensis sp. n. is characterised by body length 2470–2960 µm, cephalic and subcephalic setae located in two separate circles and almost equilong, amphidial fovea circular, situated at level of junction of buccal cavity and pharynx, secretory-excretory pore situated slightly anterior to nerve ring, spicules 1.1–1.2 cloacal body diameters long, tail subcylindrical, 4.8–5.7 cloacal body diameters with two rows of subventral setae and two pairs of subdorsal setae near tail tip in males, and tail conical without setae in female.

Remarks. The new species resembles E. paraschneideri Leduc and Zhao 2023 in the body size, arrangement of cephalic setae, and amphidial fovea position, but differs from E. paraschneideri by longer cephalic setae (3.5–4 µm vs 2–3 µm), smaller amphidial fovea (4 µm vs 5–6 µm wide), longer spicules and gubernacular apophyses (1.1–1.2 cloacal body diameter vs 0.8 cloacal body diameter and 15–17 µm vs 13 µm long in the latter species). In addition, the new species differs from E. paraschneideri in the shape of spicules (spicules slender without central hollow vs spicules stubby with a central hollow). The new species is also similar to E. schneideri Turpeenniemi 1997 and E. chesapeakensis ( Timm 1954) Tchesunov and Miljutin 2006 , but differs from E. schneideri by almost equal length of cephalic setae and subcephalic setae (4 µm) vs unequal lengths of two circles of cephalic setae and subcephalic setae (2–3 + 5–6 µm), the position of the secretory-excretory pore relative to the nerve ring (anterior to nerve ring vs posterior to nerve ring in E. schneideri ), distribution and length of somatic setae (4 µm long and mostly present in pharyngeal and cloacal regions vs 2–13 µm long and present throughout body, longer spicules and gubernacular apophyses (36–37 µm vs 25 µm and 15–17 µm vs 12 µm)), and higher values of b (12.9–15.2 vs 9–10 in E. schneideri ). The new species differs from E. chesapeakensis by lower values of a (76.3–83.5 vs 91.2–100 in E. chesapeakensis ) and lower values of c of males (14.2–17.1 vs 24.1–30), posterior position of amphidial fovea (situated at level of junction of buccal cavity and pharynx vs posterior half of the buccal cavity), and spicules without velum vs spicules with velum in E. chesapeakensis . Eleutherolaimus sinensis sp. n. differs from E. conoicaudatus sp. n. by larger body size (2670–2960 µm vs 1770–1900 µm), larger values of a (76.3–83.5 vs 41.3–46.6), slightly excretory pore (arrow 1) and cardia (arrow 2); (c) tail region, showing anus (arrow) and caudal glands; (d) tail posterior part of male 2, showing subventral setae; (e) tail tip of male 2, showing terminal setae. Scale bars: a, d, e = 10 µm; b, c = 20 µm.

longer and equilong spicules (36–37 µm vs unequal length, 30–35 µm), and slightly longer tail (c′ = 4.8–5.7 vs 3.1–4.2).