Metadesmolaimus bulbosus, Li & Ban & Huang, 2023

Li, Ting, Ban, Shuyan & Huang, Yong, 2023, Two new species of Xyalidae Chitwood, 1951 (Nematoda, Monhysterida) from Chinese Sea Area, Zootaxa 5369 (2), pp. 255-268 : 261-264

Metadesmolaimus bulbosus sp. nov.

LSID: urn:lsid:zoobank.org:act:FC147C32-C8E7-422B-869C-2C5A9C0C6E6F

( Figures 3–5 , Table 2)

Holotype and paratype material. Four males and two females were obtained and measured. Holotype male on slide YST86-1-12 . Paratype 1 (male) on slide YST40-1-3, paratype 2 (male) on slide WWJT35-1 - 8 , paratype 3 (male) on slide WWJT186-2 - 6 , paratype 4 (female) on slide WWJT58-1 - 6 and paratype 5 (female) on slide WWJT186-1 - 5 .

Type locality and habitat. Holotype and paratypes were all collected from intertidal fine sandy sediments at Beihai Silver Beach in the Beibu Gulf of the South China Sea (109°44′49′′ E, 21°14′42′′ N) in February 2021 .

Etymology. The species epithet is derived from the Latin bulbosus , meaning polyglobular, referring to its prominent bulb-like muscular swellings in the pharynx.

Measurements. All measurement data are given in Table 2.

Description. Males. Body cylindrical, brownish ( Figure 5 ). Cuticle transversely striated, about 1 µm between two striations. Lips high, with six inner labial setae, 4–6 µm long. Six outer labial setae and four cephalic setae arranged in one circle. Outer labial setae 17–19 µm long; cephalic setae 9–12 µm long. Numerous long somatic setae in pharyngeal region, 20–35 µm long. Amphids difficult to distinguish, circular, 7 µm in diameter (27% of the corresponding body diameter), situated posterior to the buccal cavity, about 24 µm from anterior end. Buccal cavity broad, extended anteriorly with an intermediate annule; anterior part cylindrical, posterior part conical, 22 µm deep and 15 µm wide. Pharynx cylindrical, with a series (18) of bulb-like muscular swellings, each with thick cuticular lining, 8–16 µm long and 17–19 µm wide. The adjacent pharyngeal bulbar swellings separated by transverse elliptic dilated structures and internal lumen. Cardia large, conical, 13 µm long. Nerve ring located at 33% –42% of the pharynx length from anterior end. Excretory pore and ventral gland not observed. Tail narrowing abruptly immediately posterior to cloaca; conico-cylindrical, 5.6–6.2 times cloacal body diameter, with several short setae. Tail tip slightly swollen, bearing two terminal setae, 10 µm long.

Reproductive system diorchic with two opposed testes, anterior testis situated to the left of intestine, posterior testis to the right. Spicules almost straight, clavated, 1.8–1.9 times cloacal body diameter in length, with broad proximal end and hooked distal end. Gubernaculum absent.

Females. Similar to males in general characteristics, except body relatively thicker (a=27–28.6 versus 37.9– 42.7), as well as buccal cavity also larger (27–30 µm versus 20–22 µm in width and 20–23 µm versus 15–17 µm in depth). Reproductive system monodelphic, ovary outstretched, reaching the base of the pharynx, located left of intestine. Post-vulval sac present, with a spermatheca. Vulva located in two thirds of the body length from anterior body extremity.

Differential diagnosis and discussion. Metadesmolaimus bulbosus sp. nov. is characterized by large buccal cavity, long cervical setae, 18 bulb-like pharyngeal muscular swellings, conico-cylindrical tail narrowing abruptly immediately posterior to cloaca, straight clavated spicules with expanded proximal end and hooked distal end and gubernaculum absent.

The new species is similar to M. zhanggi Guo, Chen & Liu, 2016 in having long somatic setae in pharynx region and narrow conico-cylindrical tail. However, it can be distinguished in several aspects. It differs from M. zhanggi by longer and slender body in males (1326–1456 µm and a=37.9–42.7 versus 930–981 µm and a=26.2–30.6), slender and not jointed outer labial setae (versus stout and jointed), narrower and longer tail (5.4–6.2 versus 4.3–5.3 cloacal body diameter), straight and clavated spicules with hooked distal end versus L-shaped spicules with pointed distal end. M. bulbosus sp. nov. differs from its other congeners by a combination of characters of multiple pharyngeal bulb-like swellings, abruptly narrowed tail, clavated spicules with expanded proximal end and hooked distal end. In addition, M. bulbosus sp. nov. is similar to Daptonema fallax ( Lorenzen, 1971) Lorenzen, 1977 and D. robustum ( Tchesunov, 1980) Tchesunov, 1990 in having large buccal cavity. However, in D. fallax , the buccal cavity lacks annule and spicules are curved and double-bent in the distal half. In D. robustum , anterior part of buccal cavity is conical, not cylindrical, the inner labial sensilla is not setiform and the gubernaculum has apophysis. The tail of M. bulbosus sp. nov. is similar to Daptonema furcatum ( Juario, 1974) Lorenzen, 1977 , but the buccal cavity of the latter species is not extended, inner labial sensilla is not setiform, spicules are S-shaped and gubernaculum has apophysis. The difference between M. bulbosus sp. nov. and its other congeners within Metadesmolaimus can be inferred from the key below.

Figures

FIGURE 3. Drawing of Metadesmolaimus bulbosus sp. nov. (A) anterior end of male; (B) entire male; (C) entire female; (D) posterior part of pharynx, showing bulbs; (E) posterior end of male, showing tail and spicule; (F) spicule. Scale bars: A, D, F 20 µm; B, C 50 µm; E 30 µm.

FIGURE 4. Micrograph of Metadesmolaimus bulbosus sp. nov. (A) anterior end of male, showing buccal cavity, inner labial setae (arrow 1) and cephalic setae (arrow 2); (B) posterior part of pharynx, showing bulbs; (C) posterior end of male, showing tail and spicules; (D) cloacal region of male, showing spicules. Scale bars: A, D 10 µm; B, C 20 µm.

FIGURE 5. Primary micrograph of Metadesmolaimus bulbosus sp. nov. (A) pharyngeal region of male; (B) posterior part of male. Scale bars: A, B 30 µm.