Zalonema eurysbucca, 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 eurysbucca sp. nov.

Figs 1 , 2 ; Tables 1 , 2

Type material.

Six males and five females were collected from Station DZ in December, 2020. Holotype: • ♂ 1 on slide DZ 20201214 2 L 18 . Paratypes: • ♂ 2 on slide DZ 20201214 2 L 101 , • ♂ 3 and ♀ 1 on slide DZ 20201214 2 L 111 , • ♂ 4 on slide DZ 20201214 2 L 102 , • ♂ 5 on slide DZ 20201214 1 L 113 , • ♂ 6 on slide DZ 20201214 2 L 117 , • ♀ 2 and ♀ 3 on slide DZ 20201214 2 L 18 , • ♀ 4 on slide DZ 20201214 2 L 110 , • ♀ 5 on slide DZ 20201214 1 L 101 .

Type locality and habitat.

All specimens were collected from the muddy sediment in the mangrove reserve of Xinying Port in Danzhou City, Hainan Province, China. The main mangrove species here is Bruguiera gymnorrhiza (L.) Lam. Characteristics of surface sediments of sampling stations are shown in Table 1 .

Etymology.

The species’ name is from the Latin ( Eurys = broad) and refers to the large buccal cavity.

Measurements.

Morphological characteristics were observed and measured under a differential contrast microscopy (NIKON 80 i) (Table 2 ).

Description.

General characteristics: Golden-brown body elongated and cylindrical, with blunt and rounded anterior extremity and conical tail. Cuticle with distinct fine annuli arranged transversely from the posterior margin of the cephalic capsule to the tail, ending in a smooth, non-annulated tail tip approximately 10 µm in length. Somatic setae short, about 1–2 µm in length, arranged in eight longitudinal rows, and each seta is connected to an epidermal gland. Cephalic capsule consists of two parts: an anterior labial region, with a thinner cuticle; and a main posterior portion, with a conspicuously thickened cuticle without annulations, which is about 15–19 µm wide in males and about 13–16 µm wide in females. Inner labial sensilla not observed; six outer labial sensilla are papilliform, arranged in a circle; four cephalic setae arranged in a circle, about 1–2 µm in length, located slightly to the back of the external labial sensilla; eight subcephalic setae, about 2–3 µm in length, arranged in a circle between the cephalic setae and the anterior margin of the amphid. Large spiral amphideal fovea and aperture, 4–4.5 turns, located laterally on the main posterior portion of the cephalic capsule, with a diameter of about 38–58 % of cbd. Buccal cavity large, with a maximum diameter of about 12–19 µm and a depth of about 34–39 µm. There are 12 cheilorhabdia arranged in a circle in the buccal cavity vestibule; the inner wall of the buccal cavity is sclerotized, with two teeth: one large dorsal tooth located at about one-third to half the depth of the buccal cavity, and one small ventral tooth at the bottom of the buccal cavity. Cylindrical pharynx with cuticularized lumen and pyriform posterior bulb; inner wall of the pharynx is thickened or sclerotized, and the pharyngeal bulb is broken into two parts. Nerve ring located at 50–63 % of the length of the pharynx. Secretory-excretory system not observed.

Males: lateral alae present on both sides of posterior body part, extending from 505–566 µm in front of anus to a position on either side of the body at the anus. Ventral ala present, extending from 250–356 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 1.13–1.34 times abd as arc, with proximal capitulum, without velum. Gubernaculum simple, without apophyses. A small cup-shaped preanal supplement located about 13 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. These structures appear to correspond to the “ small, pore-like, not cuticularized ” features reported by Leduc (2022). In the present study, these pore-like depressions were clearly observed to be arranged regularly along the ventral ala, extending anteriorly along the body, and aligning with the pattern of somatic setae in regions where ventral ala are absent. In addition, each pore-like depression extends subcutaneously and connects to the epidermal gland, similar to the association seen in somatic setae. Therefore, we interpret these pore-like structures on the ventral ala not as preanal supplements, but likely as pore-like sensilla that may be homologous to somatic setae. Preanal setae not observed. Conical tail without terminal setae, length about 1.43–1.82 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 2.4–3.4 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 48–51 % of the body length.

Diagnosis.

Zalonema eurysbucca sp. nov. is distinguished by the following combination of characters: golden-brown body (length 1772–2309 µm) with a finely annulate cuticle; short somatic setae arranged in eight longitudinal rows; eight subcephalic setae (2–3 µm) arranged in a circle between the cephalic setae (1–2 µm) and the amphid’s anterior margin; amphideal fovea (4–4.5 turns) located laterally on the cephalic capsule’s posterior portion (diameter 38–58 % of cbd); a large, cup-shaped buccal cavity with twelve cheilorhabdia, a cuticularized dorsal tooth, and a minute ventral tooth; and a conical tail. Males possess lateral and ventral alae; the arcuate spicules measure 1.13–1.34 times the anal body diameter (abd); gubernaculum simple without apophyses; a small cup-shaped preanal supplement, and the surface of the ventral ala at the position of the somatic setae sunken into small pore-like depressions.

In accordance with the classification proposed by Gharahkhani et al. (2021), the new species Zalonema eurysbucca sp. nov. belongs to Group I, which is characterized by the presence of lateral alae and / or ventral ala on the posterior part of the male body. Zalonema eurysbucca sp. nov. is distinguished by the combined presence of both lateral and ventral alae, contrasting with Zalonema ditlevseni ( Micoletzky, 1922) Gerlach, 1963 and Zalonema megalosoma (Steiner, 1918) Gerlach, 1963 , which possess only lateral alae and lack a ventral ala (in contrast to Gharahkani’s classification that places Zalonema megalosoma in Group II, the redescription of this species by Gerlach (1963) reports the presence of lateral alae in males); and from Zalonema myrianae Verschelde & Vincx, 1996 , which lacks lateral alae but possesses ventral ala. Zalonema eurysbucca sp. nov. can also be differentiated from other species in Group I. Zalonema eurysbucca sp. nov. differs from Zalonema mariae Larrazábal-Filho, Silva & Esteves, 2015 in having eight subcephalic setae (vs four), a cup-shaped buccal cavity with a single large dorsal (at 30–50 % depth) and small ventral teeth (vs. elongate buccal cavity with two dorsal teeth, one after the other), and spicules lacking a velum ( Larrazábal-Filho et al. 2015); from Zalonema vicentei Larrazábal-Filho, Silva & Esteves, 2015 in the subcephalic setae position (between cephalic setae and the anterior margin of the amphid vs. at amphid posterior margin) and number (8 vs. 4) ( Larrazábal-Filho et al. 2015); from Zalonema iranicum Gharahkhani, Pourjam, Leduc & Pedram, 2021 in the dental formula (one dorsal and one ventral tooth vs 3 teeth, a large anterior dorsal tooth, a small posterior dorsal tooth, and a medium-sized ventral-subventral tooth) ( Gharahkhani et al. 2021); from Zalonema supplementorum Gharahkhani, Pourjam, Leduc & Pedram, 2021 in the subcephalic setae count (8 vs 4) and amphid coils (4–4.5 vs 3 turns) ( Gharahkhani et al. 2021); and from Zalonema sesokoensis Leduc, 2022 by lacking amphid sexual dimorphism and possessing a larger buccal cavity ( Leduc 2022).

Figures

Figure 1. Drawing of Zalonema eurysbucca sp. nov. (lateral view). A. Male tail region, showing copulatory structure, ventral ala and preanal supplement; B. Male head end; C. Female head end; D. Female tail region; E. Female body part, showing ovaries; F. Female body. Scale bars: 50 μm (A – D); 125 μm (E); 100 μm (F).

Figure 2. Microscopic images of Zalonema eurysbucca sp. nov. (lateral view). A. Male head region, showing cheilorhabdia in buccal cavity; B. Male head region, showing buccal cavity, large dorsal tooth and minute ventral tooth; C. Male amphid; D. Male anterior region, showing longitudinal rows of short somatic setae; E. Male pharynx and the pyriform posterior bulb; F. Male posterior region, showing lateral alae, the end of ventral ala and the tail; G. Male posterior region, showing copulatory structure, supplement and ventral ala; H. Female vulva; I. Female middle region, showing longitudinal rows of short somatic setae; J. Female tail; K. Male total body; L. Female total body. Scale bars: 10 μm (A – D, G – I); 50 μm (E); 100 μm (F, J – L)