Tobrilus elginus, Naumova & Gagarin, 2019

Naumova, Tatyana V. & Gagarin, Vladimir G., 2019, Two new nematode species of the genus Tobrilus Andrássy, 1959 (Nematoda, Triplonchida) from Lake Baikal, Russia, European Journal of Taxonomy 579, pp. 1-13 : 3-7

Tobrilus elginus sp. nov.

urn:lsid:zoobank.org:act:0248B1A1-53A2-4EFD-97E4-E8AD0F6D030C

Figs 1–2 , Table 1 (morphometric)

Diagnosis

Tobrilus elginus sp. nov. is characterized by a 2200–2995 µm long body; cuticle smooth under light microscope; crystalloids absent; inner labial sensillae papilliform; six outer labial sensillae in the shape of smooth non-articulated setae 14–17 µm long, 45–57% for males and 44–59% for females of labial region width; four cephalic sensillae on the shape of thin and smooth setae 6–8 µm long; buccal cavity spacious, funnel-shaped; dorsal pocket and its tooth absent; both subventral pockets overlapping adjacent to each other. Spicules comparatively thick, slightly curved, short, 50–53 µm long, 1.1–1.3 long as the cloacal body diameter; gubernaculum in the shape of ‘gutter’; precloacal supplements 6 in number, small, submerged; tail slender, long, elongate-conical, with terminal seta.

Type material

Holotype

RUSSIA • ♂; Lake Baikal (Maloye More Strait), Elginsky Bay; 53°09′14″ N, 107°10′26″ E; 30 cm depth; 16 Jul. 2018; sand; HM RAS slide reference number 102/69.

Paratypes

RUSSIA • 2 ♂♂, 1 ♀; same collection data as for holotype; HM RAS slide reference number 102/69 (1507-1, 1507-3, 1507-5) • 7 ♂♂, 13 ♀♀; same collection data as for holotype; LIN-SB .

Etymology

The specific epithet means ‘from Elga’, the type locality name.

Description

Male

Body comparatively long and thin. Cuticle smooth under light microscope, 1.5–2.0 µm thick. Body diameter at the posterior pharynx end 1.7–2.0 times the width of the labial region. Crystalloids absent. Somatic setae rare and short, 5–7 µm long. Labial region slightly offset from the adjacent body; lips well developed. Six inner labial sensillae papilliform. Six outer labial sensillae in the shape of smooth, non-articulated setae 14–17 µm long, 45–57% of labial region width. Four cephalic sensillae in the shape of thin and smooth setae, 6–8 µm long. Both circles of setae drawn close together. Cheilostom of the average size. Buccal cavity spacious, funnel-shaped, with thick walls. Dorsal pocket and its tooth absent. Both subventral pockets overlapping adjacent to each other. Its teeth small, close to each other (~ 5 µm away). Stoma 1.1–1.3 times as long as labial region width. Amphidial fovea cup-shaped, opening at the level of buccal cavity. Pharynx muscular, comparatively long, expanding gradually along entire length. Cardiac glands large, rounded, 20–23 µm in diameter. Ventral gland, its canal, ampulla and excretory pore not seen.

Testes paired, opposed, situated to the left of intestine; anterior testes outstretched, posterior testis reflexed. Vas deferens well developed. Spicules thick, slightly curved, short, 1.1–1.3 times as long as the cloacal body diameter, apically bifurcate. Gubernaculum in the shape of ‘gutter’, 42–53% of the spicule length. Precloacal supplements 6 in number, small, submerged. Supplement ampulla flattened, contents concentrated at ampulla base. Supplement cap absent. Central thorn protruding slightly above cuticle. Supplements approximately identical in size and situated about equidistant from each other. The closest to cloaca supplement at 21–30 µm away from it; supplement row 355–435 µm long. Tail slender, elongate-conical, with terminal seta 6–8 µm long. Caudal glands well developed; spinneret in the shape of a short, conical tube.

Female

General morphology similar to that of males in structure of cuticle and anterior body end. Cardia small, surrounded by three round glands. Prerectum not observed. Rectum length equal to or slightly greater than anal body diameter. Reproductive system didelphic, amphidelphic. Ovaries situated to the left of intestine, reflexed and comparatively short. Oocytes numerous. Vulva a transverse slit and situated slightly posterior to mid-body. Vulval lips not sclerotized and not protruding outside the body contour. Cuticular wrinkles around vulva and vulva glands not seen. Vagina short, with thick walls. Uterus containing numerous spermatozoa and 1– 2 eggs, measuring 65–105 × 26–50 µm. Tail slender, long, elongate-conical, with terminal seta. Caudal glands well developed.

Remarks

Tobrilus elginus sp. nov. is most similar to T. amabilis and T. bekmanae . The new species differs from the first species in the shorter body (♂ L = 2.2–2.8 mm, ♀ L = 2.2–2.9 mm vs ♂ L = 2.8–3.0 mm, ♀ L = 3.0– 3.1 mm in T. amabilis ), shorter spicules (50–53 µm long vs 55–58 µm long in T. amabilis ), longer gubernaculum (20–26 µm long vs 16–17 µm long in T. amabilis ), shorter supplement row (355– 435 µm long vs 487 µm long in T. amabilis ) ( Tsalolikhin 1974). Tobrilus elginus sp. nov. differs from T. bekmanae in the shorter body (♂ L = 2.2–2.8 mm, ♀ L = 2.2–2.9 mm vs ♂ L = 2.6–3.1 mm, ♀ L = 2.9–3.8 mm in T. bekmanae ), thinner body (♂ a = 39–56, ♀ a = 37–46 vs ♂ a = 25–40, ♀ a = 28–35 in T. bekmanae ), shorter tail (♂ c = 14.2–18.7, c ʹ = 3.3–4.4, ♀ c = 11.0–13.4, c ʹ = 5.0–6.9 vs ♂ c = 8.5–13.7, c ʹ = 6, ♀ c = 7.4–10.0, c ʹ = 9 in T. bekmanae ), a more posterior vulva (V = 57–64% vs V = 41–50% in T. bekmanae ), shorter supplement row (355–435 µm long vs 334 µm long in T. bekmanae ) ( Tsalolikhin 1975).

Figures

Fig. 1. Tobrilus elginus sp. nov. A. Male anterior end. B. Male pharyngeal region. C. Female posterior body end. D. Male posterior body end. E. Female vulva region. Scale bars: A = 20 µm; B, E = 100 µm; C–D = 50 µm.

Fig. 2. Tobrilus elginus sp. nov., light micrographs. A. Entire male. B. Entire female. C. Male pharyngeal region. D. Male anterior end. E. Female anterior end. F. Female vulva region. G, I. Male posterior body end. H. Male supplement region. J. Female posterior body end. Scale bars: A–B = 500 µm; C, F = 100 µm; D–E, H = 10 µm; G = 20 µm; I–J = 50 µm.