Labronema porosum, Vu & Elshishka & Nguyen & Le & Mladenov & Peneva, 2024

Vu, Tam T. T., Elshishka, Milka, Nguyen, Anh D., Le, Thi Mai Linh, Mladenov, Aleksandar & Peneva, Vlada, 2024, Two new species of genus Labronema Thorne, 1939 (Nematoda, Dorylaimidae) from natural parks of Vietnam with an identification key to the species with a medium-sized odontostyle, ZooKeys 1215, pp. 1-26 : 1-26

Labronema porosum sp. nov.

Labronema glandosum sensu Vu and Nguyen (2013) .

Material examined.

Five females from the Natural Reserve Du Gia (Bac Me District, Ha Giang Province) in good condition.

Description.

Females (for measurements see Table 1 , Figs 1 – 3 ) Nematodes of a medium size. Body cylindrical, slightly ventrally curved after fixation. Cuticle three layered, especially obvious at caudal region, outer layer thin, intermediate – much thicker than the outer one, particularly at the caudal region; inner layer much thinner than the intermediate layer, especially distinct at the caudal region; cuticle 4–7 μm thick at anterior region, 5–7 μm at mid-body, and 7–9 μm posterior to anus. The intermediate layer with longitudinal striations seen at a certain optical section. Ventral and lateral pores conspicuous, present along the whole body, between fifth and sixth ventral pore a rudimentary duct was observed (at 95–112 µm from anterior end); dorsal pores 5–7 at anterior end. Lip region truncated, laterally weakly angular, offset by an appreciable constriction, 2.8–3.1 times wider than high, less than one-third (23–28 %) of body diameter at pharynx base. Lips separated, outer labial and cephalic papillae very low, inner labial papillae slightly protruding. Amphid with stirrup-shaped fovea; its aperture 9–10.5 μm wide, occupying two-fifths to almost one-half (39–47 %) of lip region diameter. Cheilostom nearly cylindrical, with thick walls. A peculiar cuticular fold present on the dorsal site of stoma, its posterior end reaching the guide ring. Odontostyle strong, 5–6 times as long as broad, 1.4–1.6 times longer than lip region diameter, and 1.7–1.9 % of total body length. Odontophore rod-like; 1.1–1.2 times odontostyle length. Pharynx conspicuously muscular, with its slender portion enlarging very gradually, the basal expansion 220–237 μm long, 45–47 % of pharynx length; dorsal nucleus (DN) at 56–60 % of pharyngeal length (n = 3). Pharyngo-intestinal junction well developed; cardia with conical projection into the intestinal lumen, measuring 46–59 × 20–25 μm. Prerectum 1.9–2.0 and rectum 1–1.2 times longer than anal body diameter. Genital system di-ovarian, with both branches well and equally developed. Ovaries large, reaching oviduct / uterus junction, with oocytes first in two or more rows and then in a single row, anterior 161–229 μm and posterior ovary 170–249 μm long, respectively. Anterior oviduct 97–180 μm long and posterior 70–120 μm long (n = 3), respectively or 1.0–2.1 and 0.7–1.4 times longer than body diameter, pars dilatata oviductus weakly developed, sphincter at oviduct / uterus junction 7–8 μm long, not cuticularised. Uteri not differentiated, tubular, sperm not present in them, anterior uterus 114–125 μm long, posterior uterus 95–100 μm long or slightly longer than the body diameter. Uterine egg observed in one female (107 × 53 μm). Vagina extending inwards to 37–45 % of the body diameter: pars proximalis vaginae measuring 20–24 × 17–20 μm, surrounded by weakly developed musculature, pars refringens consisting of two small triangular sclerotized pieces (lateral view), with a combined width of 17–20 μm; pars distalis 7.5–9.0 μm long. Vulva a longitudinal slit, 8–10 µm long. Tail short, rounded. Hyaline part of tail 11–17 μm thick or 40–65 % of total tail length.

Male. Unknown.

Remarks.

This species is very close to the Vietnamese populations identified as L. glandosum and described by Vu and Nguyen (2013). It differs only in a slightly wider lip region (22–24 vs 21–22 µm) and somewhat longer odontostyle (35–37 vs 29–35 µm). The odontostyle of the specimens of Cuc Phuong population were measured again and an error was detected in the length of the shortest odontostyle, thus the range of odontostyle length becoming 32–35 µm. The Vietnamese specimens differ from these of the type population of L. glandosum by having a longer body (L = 1.6–2.25 vs 1.41–1.58 mm), odontophore (40–50 vs 38–39 µm), pharynx length (437–513 vs 407–420 µm) and tail (25–30 vs 21–24 µm). Besides, the lateral chord is without vs with gland-like structures in L. glandosum . Since there are no significant differences based on morphology between the new species and the previously reported Vietnamese populations of L. glandosum ( Vu and Nguyen 2013) , these two populations are considered conspecific.

Type locality and habitat.

A pristine mountain area in the Natural Reserve Du Gia , Bac Me District, Ha Giang Province, Vietnam (22 ° 43 ' 5 " N, 105 ° 12 ' 4 " E, elevation 750 m a. s. l.)

Type material.

The holotype female and four paratype females are deposited in the Nematode Collection of the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria, under an accession number IBER-BAS NTC 110 .

Representative DNA sequences.

After sequencing the obtained L. porosum sp. nov. rDNA sequence fragments were deposited in GenBank under the following accession numbers: PP 084891 (18 s rDNA) originating from NR Bac Me, Ha Giang, Vietnam, and PP 060468 (NR Bac Me, Ha Giang, Vietnam), PP 060470 (NP Cuc Phuong, Ninh Binh, Vietnam) (28 S rDNA).

Etymology.

The species name reflects conspicuous ventral and lateral body pores characteristic of the species.

Differential diagnosis and relationships.

The new species is characterised by its medium-sized body (1.6–2.25 mm), and odontostyle (32–37 μm), weakly angular and offset by a constriction lip region, 21–24 μm wide, presence of a peculiar cuticular fold on the dorsal side of stoma, not differentiated uterus, a longitudinal vulva (V = 48.5–59 %), and short and rounded tail (25–30 μm, c = 53–90, c’ = 0.5–0.6). In having medium body size (L = 1.5–2. 5 mm) and odontostyle (32–39 µm), and lip region offset by a constriction, the new species resembles L. andrassyi Gagarin, 1992 , L. brevicauda Furstenberg, Heyns & Swart, 1993 , L. gerlachi Andrássy, 2011 , L. glandosum , and L. obesum Thorne, 1974 . The new species can be differentiated from all of them by having a peculiar cuticular fold on the dorsal part of the stoma. Further, it differs from:

L. andrassyi by having: a somewhat shorter body length (1.6–2.25 vs 2.1–2.7 mm), narrower lip region (21–24 vs 36–38 μm), shorter prerectum and tail (1.6–2.1 vs 3.5–5.4 times longer than anal body diameter, 25–30 vs 35–45 μm respectively) ( Gagarin 1992);

L. brevicauda by having different shape of amphidial fovea (stirrup vs funnel shape), less robust odontostyle (5–6 vs 4 times as long as broad), absence of disc-shaped structure between pharynx and cardia vs present, smaller vulva (8–10 vs 13 or 14 µm long) stippled area large vs small ( Furstenberg et al. 1993);

L. gerlachi by having: a somewhat wider lip region (21–24 vs 21–22 μm), more posterior vulva position (48.5–59 vs 45–48 %), rectum straight vs angular, a longer prerectum (1.6–2.1 vs 1.3–1.4 anal body widths) and shorter tail (25–30 vs 30–35 μm, c = 53–90 vs 51–53) ( Andrássy 2011 b);

L. glandosum by having: a longer body (1.6–2.25 vs 1.41–1.58 mm), absence of a disc-shaped structure between pharynx and cardia vs present, lateral chord ornamentation (without vs with gland-like structures), wider lip region (21–24 vs 20–21 μm), somewhat longer odontostyle (32–37 vs 32–35 μm) and tail (25–30 vs 21–24 μm) ( Rahman et al. 1986);

L. obesum by having: weakly vs strongly angular lip region, absence of a disc-shaped structure between pharynx and cardia vs present, tail longer (25–30 vs 37 μm, calculated from the drawing), and without vs with distinctive central core ( Thorne 1974).

Figures

Figure 1. Line drawings of Labronema porosum sp. nov. female A, C, D, G lip region (C holotype) B, F amphids (B holotype) E pharyngo-intestinal junction (holotype) H, I tail ends (H holotype) J vulval region K anterior genital branch (holotype). Scale bars: 25 µm (A – J); 50 µm (K).

Figure 3. Photomicrographs of Labronema porosum sp. nov. females A posterior uterus B, D, E tail ends C lateral field. Scale bars: 200 µm (A); 50 µm (B, C); 30 µm (D, E).