Allodiplogaster media, Gusakov, Vladimir A. & Gagarin, Vladimir G., 2016

Gusakov, Vladimir A. & Gagarin, Vladimir G., 2016, Two new species of nematodes (Nematoda) from highly mineralized rivers of Lake El'ton basin, Russia, Zootaxa 4161 (2), pp. 261-270 : 266-269

Allodiplogaster media sp. n.

( Figs 3 , 4 ; Table 2 )

Type material. Holotype male, inventory slide number 102/53, deposited in the nematode collection of the Helminthological Museum RAS, Institute of Ecology and Evolution , Center of Parasitology , Russian Academy of Sciences, Moscow, Russia.

Paratypes. Five mature females and eight mature males deposited in the same collection as the holotype. Three males and two females deposited in nematode collection in the Institute for Biology of Inland Waters, RAS (Borok, Russia).

Measurements. Table 2 .

Type locality. Russia, Volgograd Province, Lake El’ton basin, river Lantsug , middle course (N 49°13.630, E 46°36.704), depth 0.25 m, black sand with detrital matter, mineralization of water 7.0 g/l, temperature 24.3 °C , pH 8.0, current is hardly appreciable. Collected on 27 May 2015 .

Etymology. The species name means “medial, middle.

Description. Male. Slender, medium sized nematodes. Cuticle thin, about 1 µm thick at mid body. Cuticle with clear transverse striation and 22–24 longitudinal ridges. Ridges are formed by pairs of short linear sclerotisations. Front end of head flattened. Labial region continuous with adjoining body. Inner labial sensillae not observed. Six outer labial sensillae in the shape of short setae, 1.6–2 µm long. Four cephalic setae about 2.5 µm long. Cheilostoma barrel-shaped, with 12 cuticularized ribs. Gymnostoma with three teeth. Dorsal tooth large, mobile, claw-like, with bifurcated apical end. Right subventral tooth pyramidal, immovable, inconspicuous. Left subventral tooth in the shape of cuticularized plate, in frontal edge serrate. Telostoma in the shape of funnel. Total stoma length 10–12 µm. Amphidial fovea slit-like, situated at level of telostoma.

Pharynx slender, sharply divided into two sections: anterior part muscular and posterior part glandular. Anterior pharynx section 1.5–1.9 times as long as posterior section. Excretory pore situated slightly posterior to nerve ring. Testis single. Spicules slender, slightly curved, with handle-like capitulum. Spicules 1.3–1.6 times as long as anal body diameter. Gubernaculum 17–20 µm long, more or less keel-shaped with attenuated end. Genital papillae ten pairs: three pairs pre-cloacal and seven pairs post-cloacal. Bursa small, rudimentary. Tail long, gradually narrowed, with filiform terminus.

Female. General morphology similar to that of male. Structure of cuticle and anterior body end as in male. Inner labial sensillae not observed. Six outer labial sensillae in the shape of short setae, 1.9–2.5 µm long. Cephalic sensillae absent. Cheilostoma with 12 cuticularized ribs. Gymnostoma with three teeth. Telostoma funnel-shaped. Pharynx slender. Anterior pharynx section 1.6–1.8 times as long as posterior section. Rectum thick-walled, provided with rectal glands. Reproductive system didelphic, amphidelphic; oocytes arranged in 1–2 rows in genital zone. Uterus long, occasionally containing numerous spermatozoa and 1– 2 eggs, 62–77×30–33 µm in size. Vagina thick-walled, occupying about 1/3 of corresponding body diameter. Vulva slit-like, equatorial. Vulva lips weakly cuticularized, not protruding. Tail long, gradually narrowing. Caudal setae absent.

Diagnosis and relationships. Allodiplogaster media sp. n. is characterized by a thin and medium sized body for the genus (L = 1020–1461 µm, a = 29–56), comparatively short outer labial setae (1.6–2.5 µm long); anterior pharynx section 1.5–1.9 times as long as posterior pharynx section; spicules 32–36 µm long, with comparatively short genital setae in males.

The new species is close to A. lupata ( Shoshin, 1989) Kanzaki, Ragsdale & Giblin-Davis, 2014 and A. mordax ( Shoshin, 1989) Kanzaki, Ragsdale & Giblin-Davis, 2014 , found in Lake Baikal (Siberia, Russia) ( Shoshin 1989). It differs from the first species in the shorter pharynx (b = 5.2–7.2 vs b = 3.8–4.6), shorter outer labial setae (1.6– 2.5 µm long vs 5.0 µm long), longer anterior pharynx section (1.5–1.9 times longer than posterior pharynx section vs 1.2–1.3 times longer) and longer spicules (32–36 µm long vs 25–30 µm long) ( Shoshin 1989). From A. mordax the new species differs in the comparatively thinner body (males a = 37–56, females a = 29–37 vs males a = 28–30, females a = 27–28), shorter pharynx (b = 5.2–7.2 vs b = 4.7–4.8) and longer spicules (32–36 µm long vs 30 µm long) ( Shoshin 1989).

Figures

FIGURE 3. Allodiplogaster media sp. n. Holotype male and paratype female. A: Entire male; B: Entire female; C: Male head; D: Female head; E: Anterior body end of male; F: Male tail; G: Female tail. (Scale bars: A, B = 150 µm; C, D = 15 µm; E, G = 50 µm; F = 30 µm).

FIGURE 4. Allodiplogaster media sp. n. Holotype male and paratype female (microphotographs) A: Entire male; B: Entire female; C: Anterior body end of male; D: Vulva region; E: Cuticle structure; F: Anterior tail end of male; G: Male tail; H: Female tail; I: Female head; J: Male head; K: Cloaca region. (Scale bars: A, B = 200 µm; C = 50 µm; D, G, H = 20 µm; E, F, I, J, K = 10 µm).

Tables

TABLE 2. Morphometrics of Allodiplogaster media sp. n. All measurements are in µm (except for the ratios a, b, c, c', V; ratio of anterior / posterior pharynx section lengths) and in the form: mean ± s. d. (range).

Character	Holotype male	Paratype males (n = 11)	Paratype females (n = 7)
L a b	1241 56 6.1	1225±136 (1020–1461) 45±6 (37–56) 6.0±0.2 (5.2–7.2)	1313±90 (1122–1405) 34±3 (29–37) 5.8±0.2 (5.3–6.1)
c c' V, %	7.9 7.3 –	8.5±0.7 (7.3–9.8) 6.3±0.8 (5.1–7.5) –	7.9±0.5 (6.8–8.4) 8.6±0.8 (7.6–9.7) 50.0±1.0 (48.8–51.7)
labial region diameter stoma length outer labial setae length	16 11 1.8	16±1 (14–17) 11±1 (10–12) 1.8±0.2 (1.6–2.1)	18±1 (17–20) 12±1 (10–14) 2.1±0.2 (1.9–2.5)
pharynx length ratio of anterior/posterior pharynx section lengths distance from pharynx base to vulva	205 1.7 –	204±10 (189–224) 1.7±0.1 (1.5–1.9) –	226±8 (212–238) 1.7±0.1 (1.6–1.8) 430±44 (342–465)
distance from vulva to anus distance from pharynx base to cloaca midbody diameter	– 878 22	– 876±125 (702–1108) 27±2 (22–31)	490±46 (404–542) – 38±2 (34–40)
body diameter at level of anus or cloaca tail length spicules length (along arc)	22 158 36	23±2 (20–27) 145±10 (126–158) 34±1 (32–36)	19±1 (18–22) 166±8 (156–181) –
gubernaculum length	20	19±1 (17–20)	–