Eutobrilus mirandus, Gagarin, Vladimir G. & Naumova, Tatyana V., 2011

Gagarin, Vladimir G. & Naumova, Tatyana V., 2011, Two nematode species of the family Tobrilidae (Enoplida) De Coninck, 1965 from Lake Baikal, Russia, Zootaxa 2815, pp. 59-68 : 60-64

Eutobrilus mirandus sp. n.

( Figs 1 , 2 ; Table 1 )

Type material. Holotype male, slide reference number 213, deposited in the collection of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences (Irkutsk, Russia)

Paratypes. One male and three females deposited in the collection of the Institute of Inland Waters Biology, Russian Academy of Sciences (Borok, Yaroslavl Province, Russia); six males and four females deposited in the collection of the Limnological Institute, Siberian Branch of Russian Academy of Sciences (Irkutsk, Russia).

Measurements. Table 1 .

Type locality. Cape Gorevoi Utes, Lake Baikal, Siberia, Russia, depth 884–897 m, bitumen sediment. Collected by submersible “MIR-2”, 19–20 August 2009.

Etymology. The species name means “amazing”, “wonderful”.

Description. Male. Body cylindrical, tapering toward both extremities. Cuticle finely annulated, 1.3–1.7 µm thick at mid-body. Crystalloids absent. Somatic setae short and scarce anteriorly; becoming longer and denser in the posterior part of the body, level with supplements and on the tail. Lips well developed, high. Inner labial sensilla papilliform. Outer labial sensilla and cephalic sensilla setiform in shape, thin and articulated, arranged in a single circle. Six outer labial sensilla 11–13 µm long, about 38–43% of labial region width. Cephalic sensilla 7–8 µm long. Cheilostom spacious; pharyngostom narrow, funnel-shaped, 12–14 µm long. Dorsal pocket and dorsal tooth not visible. Both subventral pockets, separate, located far apart. Teeth in pockets are comparatively small. Stoma 25–27 µm long, 0.7–0.9 labial region width. Amphidial fovea cup-shaped, amphid aperture located at the level of stoma pockets. Cervical setae absent. Pharynx muscular, comparatively long, expanding gradually towards its base. Nerve ring encircles pharynx at 43–48% of pharyngeal length. Cardia small, surrounded by 3 oval glands. Renette, renette canal, ampulla and excretory pore not observed. Testes paired, opposed, situated to the left of intestine; anterior testis outstretched, posterior testis reflexed. Vas deferens well developed. Spicules 1.0–1.2 times as long as the cloacal body diameter, slender, slightly ventrally curved, with elongate-oval capitulum. Apical end of spicules bifurcated. Gubernaculum short, 14–16 µm long, with apical expansion. Precloacal supplementary organs echinate, 6 to 7 in number. Supplement ampullae slightly flattened, contents concentrated at ampulla basis. Supplement pads armed with small thorns (approximately 40–50 things) and one longer and thicker thorn, which protrude from the cuticle. Supplements arranged in two groups [2 + 4 (5)]. Row of supplements 221–300 µm long. Tail slender, long, with proximal conical and distal cylindrical portions, gradually merging into one another. Distal portion 1.5–1.7 times longer than proximal portion. Caudal setae 8–10 µm long, arranged in 5–6 subventral and 3–4 subdorsal pairs. Three caudal glands present, opening through short spinneret. Tail terminus with subterminal setae.

Female. General morphology is similar to that of males in structure of cuticle and anterior body end. Cuticle finely annulated. Somatic setae short and scarce. Crystalloids and cervical setae absent. Labial region comparatively wide. Lips well developed, high. Inner labial sensilla papilliform. Six outer labial sensilla and four cephalic sensilla setiform in shape, thin and articulate, arranged in a single circle. Outer labial sensilla are longer than cephalic sensilla; outer labial sensilla as long as 38–42% of labial region width. Cheilostom is comparatively small. Buccal cavity narrow, funnel-shaped; somewhat longer than the labial region diameter. Dorsal pocket and dorsal tooth not visible. Both subventral pockets small, separated and located far apart. Teeth in the pockets are comparatively small. Amphidial fovea cup-shaped, amphidial opening located at the level of buccal cavity. Pharynx muscular, comparatively long, expanding gradually towards its base. Cardiac glands large, 30–35 µm long. Renette and canal, ampulla and excretory pore not observed. Rectum 1.0–1.2 times as long as the anal body diameter. Reproductive system didelphic, amphidelphic. Ovaries situated to the left of intestine, reflexed and comparatively short. Oocytes numerous. Vulva a transverse slit, situated anterior to midbody, relatively close to anterior body end. Vulval lips sclerotized, protruding outside the body contour. Vulval glands not seen. Vagina short, its walls thin, not muscular. Uterus spacious, containing numerous spindle–shaped spermatozoa and 3–8 intrauterine eggs, measuring 71–107 × 40–61 µm. Tail long and slender, gradually narrowing towards the terminus. Caudal glands and spinneret well developed. Tail terminus with subterminal setae.

Diagnosis. Body 2.36–3.15 mm long in male, 2.96–3.71 mm long in female. Cuticle finely annulated. Crystalloids absent. Outer labial setae and cephalic setae arranged in single circle. Outer labial setae longer than cephalic setae and as long as 38–43% of labial region width. Cheilostom comparatively small. Buccal cavity narrow, funnelshaped. Dorsal pocket absent. Subventral pockets separate, with small teeth. Vulva a transverse slit, situated relatively anterior along the body length. Uterus with numerous spermatozoa and 3–8 intrauterine eggs, measuring 71– 107 x 40 –61 µm. Males with comparatively short, slightly curved spicules and short gubernaculum. Precloacal supplements 6 to 7 in number, echinate, separated in two groups [2 + 4 (5)]. Tail slender, comparatively long, with subterminal setae.

Differential diagnosis. Eutobrilus mirandus sp. n. differs from all species of the genus Eutobrilus by its markedly anterior vulva position (V = 26–31% versus 39–55% in other species of the genus). The new species is similar to E. andrassyi Altherr, 1963 in body size and stoma structure, but differs from it in the absence of crystalloids, comparatively thicker body (males, a = 32–45 versus a = 60–75 in E. andrassyi ), shorter stoma (males, stoma 26– 27 µm versus 35–40 µm in E. andrassyi ) and longer spicules (48–53 µm versus 40 µm in E. andrassyi ) ( Altherr 1963; Tsalolikhin 1983, 2005; Gagarin 2009; Zullini, 2006).

Figures

FIGURE 1. Eutobrilus mirandus sp. n., holotype male and paratype female. A: female, entire body; B: male, entire body; C: male tail; D: male head; E: spicules and gubernaculum; F: supplement; G: female tail. Scale bars: A, B = 250 µm; G = 100 µm; C = 50 µm; D – F = 20 µm.

FIGURE 2. Eutobrilus mirandus sp. n. A: male, entire body B: female, entire body; C: male tail; D: tip of the tail; E: vulval region with intrauterine eggs; F: male head; G: supplements. Scale bars: A = 200 µm; B, C, E = 100 µm; D, F, G = 20 µm.

Tables

TABLE 1. Morphometrics of Eutobrilus mirandus sp. n. (all measurements are given in µm unless otherwise stated, except for the ratios a, b, c, c’, V, spic. cl, and n. eg.).

Character	Holotype male Paratype males (n = 8)	Paratype females (n = 7)
L a	range mean 2743 2358–3146 2756 39 32–45 38	range mean 2959–3706 3236 31–48 39
b c c’ V,% diam.c.s. diam.midb.	6.0 5.1–6.0 5.5 15.1 13.4–20.2 16.5 4.0 3.4–4.4 3.9 – – – 29 29–31 30 71 64–78 71	5.8–7.1 6.3 9.1–12.0 10.8 5.0–8.8 7.2 25.7–30.8 28.7 31–34 32 73–100 84
a.d. o.l.s.	46 39–46 42 12 10–12 11	37–52 42 11–13 12
c.s. st.l.	7 7–8 7 27 25–27 26	7–9 8 26–31 28
st.w.	10 9–10 10	11–12 12
am.w.	9 8–9 8	8–10 9
dis.am. ph.l. dis.ph.cl. dis.ph. v. dis .v.a.	19 15–25 21 455 455–520 486 2106 1742–2470 2106 – – – – – –	20–25 23 445–572 515 – – 364–494 416 1807–2340 2005
Q1 Q2 n.eg. spic.	– – – – – – – – – 51 48–53 51	247–390 299 398–546 460 1–5 2 – –
spic.cl gub.l. n.sup. l.sup.r. t.l.	1.1 1.1–1.3 1.2 22 20–22 21 6 6–7 6 226 219–300 162 182 150–182 164	– – – – – – – – 255–338 300