Paratrilobus aquaticus, Naumova & Gagarin, 2020

Naumova, Tatyana V. & Gagarin, Vladimir G., 2020, Two new nematode species of the genus Paratrilobus Micoletzky, 1922 (Nematoda, Triplonchida) from the water area of Lake Baikal (Russia), European Journal of Taxonomy 723, pp. 159-172 : 165-169

Paratrilobus aquaticus sp.nov.

urn:lsid:zoobank.org:act:AB5F0913-BB36-403D-A732-AEFBB93CA939

Figs 3–4 , Table 2

Diagnosis

Paratrilobus aquaticus sp. nov. is characterized by a 2015–2203 µm body length; cuticle finely annulated; crystalloids absent; six inner labial sensillae papilliform; six outer labial sensillae in the shape of smooth non-articulated setae 18–20 µm long (53–58% of labial region width); four cephalic sensillae in shape of thin and smooth setae 10–13 µm long; buccal cavity spacious, barrel-shaped; one pocket connected with buccal cavity by wide gleam and contains two small teeth. Spicules comparatively thin, 51 µm long, 1.2 times as long as cloacal body diameter; gubernaculum in shape of ‘gutter’. Precloacal supplements 6 in number, about same size, located approximately at identical distance from each other; supplements echinate, not very protruded over body surface; contents of ampulla located at base; cap armed, numerous small thorns and one large central thorn. Tail slender, comparatively long; three caudal glands and spinneret well developed; subterminal seta not observed.

Etymology

The species epithet comes from the habitat ('water').

Material examined

Holotype

RUSSIA • ♂; Lake Baikal , Posolsk Bank (underwater elevation of the bottom between the southern and central basins of Lake Baikal); 52.07994° N, 105.90368° E; 51 m depth; 5 Jul. 2012; T.V. Naumova leg.; sand and silt; HM RAS, slide 102/64 ( 768-2 ).

Paratypes

RUSSIA • 3 ♀♀; same collection data as for the holotype; T.V. Naumova leg.; LIN–SB ( 765-3 , 765-5 , 767-5 ) • 1 ♀ same collection data as for the holotype; T.V. Naumova leg.; HM RAS slide 102/64 ( 768-4 ) .

Description

Male

Body comparatively short. Cuticle finely annulated, 1.5 µm thick. Crystalloids absent. Somatic setae sparse, short. Labial region comparatively high, slightly offset from adjacent body, lips well developed. Six inner labial sensillae papilliform. Six outer labial sensillae in shape of smooth setae long 53% of labial region width. Four cephalic sensillae in shape of thin setae. Cheilostom of average size. Buccal cavity spacious, barrel-shaped, with thick walls. One pocket connected with buccal cavity by wide gleam, containing two small teeth. Stoma 1.5 times as long as labial region width. Amphidial fovea cupshaped, opening at level of buccal cavity. Pharynx muscular, comparatively long, expanding gradually along length. Cardiac glands large, rounded, 30 µm in diameter. Ventral gland, its canal, ampulla, excretory pore not observed.

Testes paired, situated to left of intestine; anterior testis outstretched, posterior testis short, reflexed. Vas deferens well developed. Spicules slender, ventral curved, 1.2 times as long as cloacal body diameter. Gubernaculum in shape of gutter, 39% of spicule length. Precloacal supplement 6 in number, about one size, located approximately at equal distances from each other. Supplements echinate, not very protruded over body surface. Ampulla contents concentrated in ampullae base. Shoulder absent. Cap armed, numerous small thorns, one large central thorn. Precloacal supplement located anteriorly to spicules level. Tail slender, comparatively long. Three caudal glands, spinneret well developed. Subterminal setae not seen.

Female

General morphology similar to that of males in structure of cuticle, anterior body end. Six outer labial sensillae in shape of smooth non-articulated setae long 53–58% of labial region width. Cardia surrounded by three round glands. Rectum length equal to or slightly greater than anal body diameter. Reproductive system didelphic, amphidelphic. Ovaries situated to left of intestine, reflexed. Oocytes numerous. Vulva transverse slit, situated slightly posterior to mid-body. Vulval lips not sclerotized, not protruded outside body contour. Cuticular wrinkles around vulva, vulva glands not observed. Vagina straight line, with well-expressed spherical vaginal chamber, thick walls. Generated eggs in uterus not observed. Tail slender, comparatively long. Subterminal seta not seen.

Remarks

Paratrilobus aquaticus sp. nov. is similar to P. granulosus Gagarin & Naumova, 2011 and P. ultimus (Tsalolichin, 1977) in the structure of the precloacal supplements. From the former species, it differs in the absence of crystalloids, a comparatively longer pharynx (b = 3.3– 3.9 vs b = 4.5–5.9 in P. granulosus ), longer outer labial setae (18–20 μm long, 53–58% of labial region width vs 6.5–8.5 μm long, 30– 35% of labial region width in P. granulosus ), the vulva position (V = 51.8–53.0% vs 39.1–46.1% in P. granulosus ), the longer stoma (48–52 µm long vs 28–33 µm long in P. granulosus ), and the absence of a subterminal seta ( Gagarin & Naumova 2011). From the latter species, it differs in the longer pharynx (b = 3.3–3.9 vs b = 4.7–5.9 in P. ultimus ), a longer and more slender tail (c = 7.5–8.9, cʹ = 5.5–6.8 vs c = 10.9–16.4, cʹ = 3.5–4.5 in P. ultimus ), the longer stoma (48–52 µm long vs 21 µm in P. ultimus ), longer outer labial setae (18–20 µm long, 53–58% of labial region width vs 6–7 µm long, 25–30% of labial region width in P. ultimus ), and the vulva position (V = 51.8–53.0% vs V = 39–43% in P. ultimus ) (Tsalolichin 1977).

Figures

Fig. 3. Paratrilobus aquaticus sp. nov. A. Male anterior end. B. Female vulva region. C. Female posterior body end. D. Male precloacal supplement. E. Male posterior body end. A, D–E: holotype (HM RAS 102/64 768-2); B–C: paratype (HM RAS 102/64 768-4). Scale bars: A = 30 µm; B = 70 µm; C = 60 µm; D = 20 µm; E = 50 µm.

Fig. 4. Paratrilobus aquaticus sp. nov., light micrographs. A. Entire male. B. Entire female. C. Female pharyngeal region.D. Male anterior end.E. Female anterior end.F. Female vulva region.G. Male cloacal region. H. Male posterior body end. I. Female posterior body end. A, D, G–H: holotype (HM RAS 102/64 768-2); B–C, I: paratype (HM RAS 102/64 768-4); E–F: paratype (LIN-SB 765-3). Scale bars: A–B = 200 µm; C, H = 50 µm; D–E = 10 µm; F–G, I = 20 µm.