Coomansus parvus ( de Man, 1880 ) Jairajpuri & Khan, 1977

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

Coomansus parvus ( de Man, 1880) Jairajpuri & Khan, 1977

Figs 1 , 2

Description.

Female [Based on 10 specimens from 3 localities; see Table 2 for measurements]. Body short, 0.70–1.15 mm, J- or C-shaped upon relaxation, body diameter at mid-body 47–53. Cuticle smooth under light microscope (very faint striation observed in one specimen, Fig. 2 H ), 2–3 thick along most of body, 3–4 thick in post-anal region. Lip region offset, cephalic and labial papillae prominent, conical, of almost same size. Amphid apertures oval, 5 ± 0.4 (4–5) (n = 6) wide, situated anterior to dorsal tooth apex, at 10–14 from anterior end. Buccal capsule oval, somewhat flattened at base, 1.6–1.9 as long as wide or 0.9–1.2 times as long as lip region width; its ventral wall 1.5–2.5 thick, dorsal wall posterior to dorsal tooth ~ 3 thick. Dorsal tooth small, its anterior margin 3.0 ± 0.5 (2–4) wide, located near middle of buccal capsule, tooth apex at 9 ± 1 (8–11) from anterior end of buccal capsule. Nerve-ring at 97 ± 6 (90–103) (n = 6) from anterior end of body. Excretory pore posterior to nerve-ring, small, well visible. Reproductive system amphidelphic. Genital branches almost symmetrical; anterior branch 134 ± 50 (80–253) (n = 9) long; posterior branch 115 ± 19 (80–133) (n = 9) long. Ovaries well developed; anterior ovary 60–105 (n = 7) long; posterior ovary 70–140 (n = 7) long. Oviduct with marked pars dilatata oviductus, ~ 30 wide. Uteri very short. Two uterine eggs present in one female measuring 81 × 40 and 90 × 38. Vagina with straight walls, its length representing 25–33 % of corresponding body width; pars refringens vaginae as 2 oval to drop-shaped smooth sclerotised pieces, 3–4 long and 2–3 wide; pars distalis vaginae ~ 3 long. Vulva a transverse slit; pars refringens vaginae protruding in some specimens (Fig. 2 I ). Rectum 0.7–0.8 times as long as body diameter at anus. Tail conoid, ventrally arcuate, with finely rounded tip. Caudal glands and spinneret absent. Caudal pores two pairs. Male: Not found.

Voucher material.

Ten specimens are deposited in the Nematological Collection of the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria, under the accession numbers IBER-BAS NC 49 / 1, IBER-BAS NC 51 / 2, IBER-BAS PN 68 / 4 litter, IBER-BAS NC 88 / 4, IBER-BAS NC 88 / 7-9. Photovouchers for the sequenced specimens are provided in Suppl. material 1: figs S 1 – S 3.

Habitats and localities.

Soil around Ulmus sp. , Populus sp. , and C. betulus and litter around F. sylvatica and Acer sp. along riverbanks of the rivers Arda, Lopushnitsa, Vedena, and Devinska (see Table 1 for details).

Representative DNA sequences.

28 S rRNA gene (GenBank: PP 768895 – PP 768898); 18 S rRNA gene (GenBank: PP 768899 and PP 768900).

Distribution.

Almost cosmopolitan, except in Australia ( Andrássy 2009). In Bulgaria, C. parvus has been reported with no morphological evidence supporting identification in soil samples from an oak forest in Burgas Province ( Aleksiev et al. 1998), from beech forests in Strandzha Mountain (Strandzha Nature Park, protected zones “ Bjalata prust ” and “ Propada ”; Iliev and Ilieva 2014), and from arable lands in Sofia ( Katalan-Gateva 1968) and Kazanlak provinces ( Katalan-Gateva et al. 1981). Iliev and Ilieva (2016) described and illustrated C. parvus based on a large population of females in soil samples from one habitat in the Rhodope Mountains. The present study provides the second documented record of C. parvus in Bulgaria, the first record of this species in litter samples, and four new localities in three provinces (Tables 1 , 2 ).

Remarks.

Morphologically, the present material belongs to and was identified as C. parvus . Some variation was detected in the present material with single specimens from three populations sampled in the Rhodope and Balkan Mountains showing lower values for L, a, G 1, G 2, the length of the genital branches, ovaries, and tail, and greater values for the distance of the amphid from anterior end compared with the population from Vitosha Mountain (Table 2 ). We consider these small metrical differences to represent intraspecific variation; this was confirmed by the very low levels of genetic divergence (see above).

The morphometric data for the present material fall within the range given by Andrássy (2011 b), except for the slightly greater values for the width of the buccal capsule (14–15 vs 10–12 µm). Comparisons with published descriptions of C. parvus revealed an overlap with the morphometric data of the present material but also a greater variation with higher upper limits of variation for the published ranges of body length ( Zullini et al. 2002; Ahmad and Jairajpuri 2010; Ishaque et al. 2022) and most of the indices, and lower ranges for the width of the buccal capsule in four populations falling below the range recorded in the present specimens (Suppl. material 2: table S 1). It is worth noting that there was an overall good agreement with the descriptions and morphometric data for a population of C. parvus collected in Bulgaria by Iliev and Ilieva (2016) and especially with a population used for generating 18 S rDNA and 28 S rDNA sequences for this species described by Tabolin and Kolganova (2020).

However, the material described by Ishaque et al. (2022) showed little overlap with the published descriptions and the present material, with ranges for a number of characters falling outside the known ranges for C. parvus : outside the upper limits of variation (L, V, buccal capsule length and width, lip region width, and rectum length); and outside the lower limits of variation (G 1, G 2, and position of tooth apex) (Suppl. material 2: table S 1). This material keys down to C. indicus Jairajpuri & Khan, 1982 in the key to species of Coomansus by Andrássy (1993, 2009) and to C. ulsani Choi, Khan & Lee, 1999 in the key by Vu (2021) but does not agree completely with the data for these species. Clearly, the material of Ishaque et al. (2022) does not belong to C. parvus but definite identification is not possible based on the available data and illustrations (also see comments in Suppl. material 2: table S 1).

Figures

Figure 1. Line drawings of Coomansus parvus (de Man, 1880) Jairajpuri & Khan, 1977. Female specimens from populations collected from riverbanks of the rivers Vedena (A, B, D) and Arda (C): A anterior region B posterior genital branch C, D tail end. Scale bar: 25 µm.

Figure 2. Photomicrographs of Coomansus parvus (de Man, 1880) Jairajpuri & Khan, 1977. Female specimens from populations collected from riverbanks of the rivers Lopushnitsa (A, B, E – G, M), Vedena (C, D, H, I, K, L), and Arda (J): A entire body B – D, G anterior region (amphid opening arrowed in G) E, F, I reproductive system (E anterior genital branch F, I vulval region showing pars refringens vaginae) H, J – M tail (cuticle striation arrowed in H; caudal pores arrowed in J and K). Scale bars: 200 µm (A); 20 µm (B – D, F – I, M); 50 µm (E, J – L).