Zalonema cylindribucca, Chen & Guo, 2025

Chen, Yuzhen & Guo, Yuqing, 2025, Two new nematode species of the genus Zalonema (Desmodorida, Desmodoridae, Desmodorinae) from mangrove wetlands, China, ZooKeys 1260, pp. 195-211 : 195-211

Zalonema cylindribucca sp. nov.

Figs 3 , 4 ; Table 3

Type material.

Five males and three females were collected from Station SY in July, 2020. Holotype: • ♂ 1 on slide SY 2020730 2 H 108 . Paratypes: • ♂ 2 & ♀ 1 on slide SY 2020730 1 L 126 , • ♂ 3 & ♀ 2 on slide SY 2020730 2 H 102 , • ♂ 4, • ♂ 5 & ♀ 3 on slide SY 2020730 2 H 108 .

Type locality and habitat.

All specimens were collected from the muddy sediment in the mangrove reserve of Yalong Bay Qingmei Port in Sanya City, Hainan Province, China. The primary mangrove species here are Rhizophora stylosa Griff. and Avicennia marina (Forssk.) Vierh.

Etymology.

The species is name for its cylindrical buccal cavity.

Measurements.

Morphological characteristics were observed and measured under a differential contrast microscopy (NIKON 80 i) (Table 3 ).

Description.

General characteristics: Body elongate-cylindrical, golden-brown in color, with a cephalic capsule and a conical tail. Cuticle with annuli arranged transversely from the posterior margin of the cephalic capsule to the tail, with tail tip about 10 µm smooth and without annuli. The annuli are spaced by about 0.6 µm at both the anterior and posterior ends of the body, and by about 0.8 µm in the middle part. Somatic setae short, 1–2 µm in length, and arranged in eight longitudinal rows. Cephalic capsule divided into two parts: an anterior labial region, with a thinner cuticle; and a main posterior portion, with a width of 8–10 µm, and its cuticle distinctly thickened without annuli. No inner labial sensilla were observed; the six outer labial sensilla are papilliform and arranged in a circle; four cephalic setae and eight subcephalic setae are each arranged in a circle, about 2–3 µm in length, with the cephalic setae located slightly posterior to the outer labial sensilla; the subcephalic setae are positioned between the cephalic setae and the anterior margin of the amphid. Large spiral amphideal fovea and aperture, 3–3.5 turns, located laterally on the main posterior portion of the cephalic capsule, with diameter about 35–41 % of cbd. Buccal cavity cylindrical, with a maximum diameter of approximately 5–6 µm and a depth of about 28–31 µm. There are 12 cheilorhabdia arranged in a circle in the buccal cavity vestibule. At the anterior part of the buccal cavity, near the base of the cheilorhabdia, there is a large dorsal tooth; and another small ventral tooth is located at the bottom of the buccal cavity, close to the esophagus. Cylindrical pharynx with cuticularized lumen and a pear-shaped posterior bulb; the inner wall of the pharynx is thickened or sclerotized, and the pharyngeal bulb slightly broken. Nerve ring located at 60–65 % of the pharynx. The excretory system was not observed.

Males: lateral alae present on both sides of posterior body part, extending from 374–410 µm in front of anus to a position on either side of the body at the anus. Ventral ala present, extending from 290–420 µm in front of anus to the anus. Reproductive system monorchic with single anterior outstretched testis located to the right of intestine. Spicules paired, equal, arcuate, length about 1.07–1.19 times abd as arc, with proximal capitulum. Gubernaculum simple, without apophyses. A small cup-shaped preanal supplement located about 8–10 µm anterior to the anus. The surface of the ventral ala is marked by small pore-like depressions located at the positions corresponding to somatic setae. However, no distinct setal structures were observed within these depressions. Preanal setae not observed. Conical tail without terminal setae, length about 1.76–2.32 times abd. Spinneret with single opening present.

Females: Most characteristics are similar to those of the males, but the tail is longer than that of the males, with a length of about 3.25–3.65 times abd. Without lateral alae or ventral ala. Reproductive system didelphic, reflexed and present on the right side of the intestine. Vulva sclerotized, located at 53–54 % of the body length.

Diagnosis.

Zalonema cylindribucca sp. nov. is distinguished by its golden-brown body color, length 1158–1451 μm; cuticle with annuli; somatic setae short and arranged in eight longitudinal rows; four cephalic setae and eight subcephalic setae are each arranged in a circle, about 2–3 µm in length; amphid spiral and 3–3.5 turns, with diameter about 35–41 % of cbd; buccal cavity cylindrical, 12 cheilorhabdia arranged in a circle in the buccal cavity vestibule; a large dorsal near the base of the cheilorhabdia, and another small ventral tooth at the bottom of the buccal cavity; male with both lateral alae and ventral ala, spicules length about 1.07–1.19 times abd as arc, gubernaculum without apophyses, a small cup-shaped preanal supplement present, and the surface of the ventral ala at the position of the somatic setae sunken into small pore-like depressions.

According to the classification by Gharahkhani et al. (2021), Zalonema cylindribucca sp. nov. belongs to Group I, which is characterized by having lateral alae and / or a ventral ala on the posterior part of the male body. The new species has both lateral alae and ventral ala on the posterior part of the male body. Therefore, it can be distinguished from Zalonema ditlevseni ( Micoletzky, 1922) Gerlach, 1963 and Zalonema megalosoma (Steiner, 1918) Gerlach, 1963 (which only have lateral alae but no ventral ala) and Zalonema myrianae Verschelde & Vincx, 1996 (which lacks lateral alae but has a ventral ala). In addition, compared with other species in Group I, the new species can be differentiated based on the number and position of subcephalic setae, the shape of the buccal cavity and the number and position of teeth in the buccal cavity, the number of turns of the amphid, and the morphology of the spicules ( Larrazábal-Filho et al. 2015; Gharahkhani et al. 2021; Leduc 2022).

Zalonema cylindribucca sp. nov. and Zalonema eurysbucca sp. nov. are quite similar in terms of the presence of preanal supplement, spicules, and the existence of lateral alae and ventral ala. However, the two species differ significantly in the shape of the buccal cavity and the location of the large dorsal tooth. Zalonema eurysbucca sp. nov. has a large buccal cavity that is wider at the top and narrower at the bottom, with the large dorsal tooth located at a depth of about one-third to one-half of the oral cavity. In contrast, Zalonema cylindribucca sp. nov. has a cylindrical buccal cavity that is almost equal in width at the top and bottom, with the large dorsal tooth situated at the anterior part of the buccal cavity, near the base of the cheilorhabdia. Additionally, the body size and relative size of the amphid differ between the two species, Zalonema eurysbucca sp. nov. has a body length of 1772–2309 μm, with a relatively shorter tail (male c = 19.3–23.65, female c = 14.55–16.67). Zalonema cylindribucca sp. nov. has a body length of 1158–1451 μm, with a relatively longer tail (male c = 15.88–17.17, female c = 10.81–13.69).

Figures

Figure 3. Drawing of Zalonema cylindribucca sp. nov. (lateral view). A. Male head end; B. Male tail region, showing copulatory structure, ventral ala and preanal supplement; C. Female tail region; D. Female head end; E, F. Male copulatory structure; G. Female body; Scale bars: 50 μm (A – F); 100 μm (G).

Figure 4. Microscopic images of Zalonema cylindribucca sp. nov. (lateral view). A. Male amphid; B. Male buccal cavity and teeth; C. Female head region, showing cheilorhabdia in buccal cavity and cephalic setae, subcephalic setae; D. Female head region, showing buccal cavity, and teeth; E. Female amphid; F. Male tail region, showing tail, supplement and ventral ala; G. Male copulatory structure; H. Female vulva; I. Male posterior region, showing lateral alae and longitudinal rows of short somatic setae; J. Male posterior region, showing lateral alae, the end of ventral ala and the tail; K. Female anterior region, showing pharynx and the posterior bulb; L. Female tail; M. Female ovaries; N. Male total body; O. Female total body. Scale bars: 10 μm (A – I); 50 μm (K, L); 100 μm (J, M – O).