Mononchus sp.

Altash, Stela, Kostadinova, Aneta & Peneva, Vlada, 2024, Integrative taxonomic study of mononchid nematodes from riparian habitats in Bulgaria. I. Genera Mononchus Bastian, 1865 and Coomansus Jairajpuri & Khan, 1977 with the description of Mononchus pseudoaquaticus sp. nov. and a key to the species of Mononchus, ZooKeys 1206, pp. 137-180 : 137-180

Mononchus sp.

Figs 10 , 11

Description.

Female [Based on 2 females; see Table 5 for measurements]. Body slender, straight, with strongly ventrally curved tail; body diameter 42 at posterior end of buccal capsule and 45–52 at mid-body. Cuticle smooth under light microscope, 3–3.5 thick along body, thicker (4–5) around vulva and posterior to anus. Lip region rounded, continuous with adjoining body; papillae small, cephalic papillae round and somewhat more visible than labial. Body at posterior end of pharynx twice as wide as lip region. Amphids with oval apertures (5 wide), located between dorsal tooth apex and anterior end of buccal capsule. Buccal capsule oblong, with flattened base, 2.3–2.4 as long as wide or 1.7–1.8 times as long as the labial diameter, its ventral wall around 3 thick, dorsal wall posterior to dorsal tooth 4 thick. Dorsal tooth robust, its anterior margin 4 wide, located at 10–11 from anterior end of buccal capsule. Ventral wall of buccal capsule with short, not well-visible rib, transverse ventro-sublateral ribs located at level of dorsal tooth apex. Excretory pore weakly marked, posterior to nerve-ring. Reproductive system amphidelphic, genital branches short. Ovaries well developed, not reaching uterus-oviduct junction. Oviduct with well-marked pars dilatata oviductus, 25 wide. Uteri short, anterior uterus 30 long, posterior uterus 36 long (n = 1). Oviduct-uterus junction with moderately developed muscular sphincter. Vagina with straight walls and small spots next to pars refringens vaginae, length representing 31 % of corresponding body width; pars refringens vaginae as two round drop-shaped sclerotised pieces with smooth surface, 4 × 2 in size; pars distalis vaginae well visible, ~ 4 long. Vulval opening round (Fig. 11 E ), vulva not protruding; vulva-anus distance equals 2.1 tail lengths. Tail long, cylindrical, strongly curved ventrad, length representing 16–18 % of body length; cylindrical part of tail ~ 6 wide. Caudal glands moderately developed, arranged in tandem. Tail tip rounded, somewhat asymmetrical, dorsal part better developed, with terminal spinneret and one large setiform papilla. Three pairs of caudal pores present. Male. Not found.

Voucher material.

Two specimens are deposited in the Nematode Collection of the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, under the accession numbers IBER-BAS NC 316 / 1.

Habitat and locality.

Soil around roots of F. sylvatica near a waterfall (River Grafska, inflow of River Kopilovtsi; see Table 1 for details).

Remarks.

Morphologically, the specimens resemble most Mononchus oblongus Andrássy, 2011 regarding the shape of the buccal capsule, the actual and relative length of the tail (as percent of body length), and the position of tooth apex (Table 5 ; Andrássy 2011 a). However, the present specimens exhibit some differences in other morphometric features and proportions such as the total body length (1.31–1.62 vs 1.60–1.88 µm), the length of the buccal capsule (45–47 vs 48–51 µm) and tail (230–263 vs 264–276 µm), the width of the lip region (25–27 vs 22–23 µm), and the ratios buccal capsule length / width (2.3–2.4 vs 2.6–2.8), buccal capsule length / lip region width (1.7–1.8 vs 2.1–2.3) and body at pharynx base / lip region width (1.9–2.0 vs 2.7–2.9).

The present specimens also show similarities with M. truncatus and M. himalayensis Rawat & Ahmad, 2000 . However, Mononchus sp. differs from M. truncatus in having a shorter body (1.31–1.62 vs 1.7–2.1 mm), a more anterior position of tooth apex (22–23 vs 25–29 %), longer tail in relation to body length (16–18 vs 10–13 %), smaller vulva-anus length / tail length ratio (2.1 vs 2.4–3.0), a lower c value (5.7–6.1 vs 7.5–8.4) and a different shape of the vulva (round vs transverse) ( Andrássy 2011 a). Differences between Mononchus sp. and M. himalayensis include a shorter body (1.31–1.62 vs 1.6–1.9 mm), a more anterior position of tooth apex (22–23 vs 25–31 %), lower a - and c ’ - values (28–31 vs 33–38 and 7.7–7.9 vs 8.8–10.4, respectively) and absence of pre-vulval papilla (vs presence) ( Rawat and Ahmad 2000). Probably the two females represent a species not yet described; however, additional specimens are needed to confirm the identity of the Bulgarian population.

Figures

Figure 10. Line drawings of Mononchus sp. female: A anterior region B vulval region and posterior genital branch C vulval region D tail. Scale bar: 25 µm.

Figure 11. Photomicrographs of Mononchus sp. females: A body, total view B – D anterior region (ventro-sublateral ribs arrowed in C; amphid opening arrowed in D) E vulval opening, subventral view F, G Pars refringens vaginae (small spots next to it arrowed in F) H reproductive system I tail tip J tail K sphincter of the oviduct-uterus junction (arrow). Scale bars: 400 µm (A); 20 µm (B – G, I, K); 50 µm (H, J).