Mesodorylaimus vietnamicus, Gagarin & Gusakov, 2014

Gagarin, Vladimir G. & Gusakov, Vladimir A., 2014, Enchodelus minor sp. n. and Mesodorylaimus vietnamicus sp. n. (Nematoda, Dorylaimida) from small freshwater bodies of Vietnam, lnternational Journal of Nematology 24 (1), pp. 23-30 : 26-30

Mesodorylaimus vietnamicus sp. n.

( Figs 3 , 4)

Measurements: See Table 2.

Male. Body comparatively short and thick. Cuticle smooth,

1.0 - 1.5 μm thick at mid-body, without longitudinal ridges; cuticular pores not seen. Lips roundish. Labial papillae small, hardly visible. Labial region comparatively high, offset from adjacent body. Amphidial fovea cup-like, occupying 67 -80% of the corresponding body diameter and situated at the base of lips. Odontostyle straight, comparatively short, 1.0 - 1.1 times as long as the labial region diameter. Its aperture 30 -35 % of its total length. Odontostyle width at its base twice more than cuticle thickness at the corresponding body level. Odontophore rodlike, 0.7 -0.8 times as long as the odontostyle. Guiding ring simple. Oesophagus muscular, expanding about the middle ofits length. Oesophageal gland nuclei indistinct. Nerve ring situated at 40 -45 % of the total oesophagus length. Cardia conoid, muscular, surrounded with intestinal tissue.

Testes paired, opposed. Spicules robust, bent ventrally, 1.3 - 1.5 times as long as the cloacal body diameter. Lateral guiding pieces spindle-shaped, 9 -11 μm long. Precloacal ventro-median Supplements in the shape of small papillae. In addition to one adcloacal pair, a series of 12 - 14 regularly spaced supplements are present; the series measuring 73 -86 μm long. Prerectum comparatively short, 2.5 -3.4 times cloacal body diameter long. Intestine-prerectum junction located in the series of ventro-median supplements. Tail short, conoid-rounded, with 3 -4 pairs of cuticular pores.

Table 2. Morphometric data of Mesodorylaimus vietnamiens sp. n. (all measurements are in μm).

Female. General appearance similar to that of males except for the tail region. Structure of cuticle and anterior body end as in males. Cuticle smooth, thin. Labial region high, offset from adjacent body. Amphidial fovea cup-like, situated at the base of lips. Odontostyle straight, comparatively short. Guiding ring simple. Oesophagus muscular, expanding about the middle of its length. Cardia conoid, muscular, surrounded by intestinal tissue. Prerectum and rectum 2.1 -2.8 times and 1.0- 1.2 times as long as the anal body diameter, respectively.

Reproductive system didelphic, amphidelphic; ovaries antidromous. Both ovaries situated at the left of intestine, comparatively long. Vulva pre-equatorial, in the shape of transverse slit. Vulva lips not sclerotized and not protruding outside the body counter. Wrinkles and folds of cuticle in the vulva region absent. Oocytes numerous, first in two rows, then in a single row. Vagina with muscular walls, extending inwards to half of the corresponding body diameter. Pars proximalis vaginae 13 - 15 μm long, with weakly sigmoid contour; pars refringens vaginae consisting of welldeveloped, head arrow-shaped or triangular with light sclerotizations; pars dislalis vaginae short. Uterus spacious, with spindle-shaped spermatozoa. Tail long, with broad basal conical portion and narrow cylindrical posterior portion. Length of cylindrical posterior tail portion 73 -80% of total length tail. Tail terminus round. Caudal pores two pairs, one subdorsal, the other subventral.

Diagnosis and relationship. Body 950 - 1137 μm in males, 952 - 1332 μm in females. Cuticle thin, smooth, without longitudinal ridges. Labial region high, offset from adjacent body. Amphidial fovea cup-like, occupying 67 -80 % of the corresponding body diameter. Odontostyle straight and comparatively short, 1.0 - 1.1 times as long as the labial region diameter. Its aperture 30 - 35% of its length. Vulva pre-equatorial, in the shape of transverse slit. Cuticular wrinkles and folds in the vulva region absent. Spicules robust, bent ventrally, 34 -36 μm long. In addition to adcloacal supplement, a series of 12 - 14 regularly spaced supplements are present. Prerectum 2.1 -2.8 anal body diameters long in females, 2.5-3.4 cloacal body diameters long in male.

Intestine-prerectum junction in males located in the region of series of ventro-median supplements. Tail in females long, with broad basal conical portion followed by narrow cylindrical posterior portion. Tail in males short, conoid-rounded.

Mcsodorylaimus vietnamiens sp. n. comes close to M. ornaıivulvaıis Abolafia & Pena-Santiago, 1997 and M. parasubrilis ( Meyl, 1957) . From the former species it differs in the comparatively thicker body (a = 18-29 vs a = 29.8- 43.6 in M. ornalivıılvalis ). shorter spicules (34-36 Wh long vs 40-54 μm long in M. ornaıivıılvaıis ), greater number of precloacal Supplements in males (13-IS vs 8-10 in M. ornuıivulvaıis ) and absence of cuticular wrinkles and folds in the vulva region in females ( Abolafia & Peña-Santiago, 1997). From M. parasııbtilis it differs in the longer body (females L = 952 - 1332 μm, males L = 846- 1185 μm vs females L í 0.8 - 1.0 mm, males L = 0.7 -0.8 mm in M. parasubtílís ), comparatively shorter tail in females (c = 7.8- 10.6 vs c = 6- 8 in M. parasııbtilis ), shorter odontostyle (10- 12 long vs 12 - 14 long in M. parasubtilis ), shorter spicules (34 -36 μm long vs 40 μm long in M. parasubtilis ), greater numbers of precloacal Supplements (13 -15 vs 8) and comparatively longer prerectum in females (2.1 -2.8 anal body diameters vs 1.5 anal body diameters in M. parasubtilis ) ( Meyl, 1957).

Type locality and habitat: Vietnam, Dong Nai (Dong Nai) Prov., Cat Tien ( Cát Tien ) National Park , a nameless small shallow forest lake (N 11 ° 27.311, E l 07 °20.l 21), altitude 131 m, white clay with plant residues, depth 0.25 m, water temperature 27 ° C, dissolved oxygen 2 mg / 1, pH 6.2, conductivity 40 μS/sm.

Type specimens: Collected on 12 May 2012 (V. A. Gusakov).

Holotype: Male, inventory slide 102/27, deposited in the Helminthological Museum, RAS, Institute of Ecology and Evolution, Center of Parasitology, Russian Academy of Sciences, Moscow, Russia.

Paratypes: Fifieen males and 15 females situated in the same inventory slide 102/27 as holotype .

Figures

Fig. 3. Mesodorylaimus vietnamicııs sp. n. Holotype male (B, C, E) and paratype females (A, D, F): A, B - general view; C - head; D - vulva region; E, F - posterior body end. (Scale bars: A, B = 100 μm; D-F = 50 μm; C = 15 μm)

Tables

Table 2. Morphometric data of Mesodorylaimus vietnamiens sp. n. (all measurements are in μm). Characters Holotype male Paratypes 15 males 15 females range mean range mean L l 135 846- 1185 1026 952- 1332 1142

Characters	Holotype male		Paratypes
		15 males		15 females
		range	mean	range	mean
L	l 135	846 - 1185	1026	952 - 1332	1142
8	23	18 -25	22	22 -29	24
b	4.9	4.2 - 5.3	4.7	4.4 - 5.5	5.0
	45.4	35.8 - 53.8	42.7	7.8 - 10.6	9.0
	0.9	0.8 - 1.0	0.9	5.2 -6.3	5.7
V				43.9 -49.8	47.5
Labial region width	10	10 - 11	10	10-ll	10
Odontostyle length	ll	10 - 12	ll	10- 12	ll
Odontophore length	8	7 - 10	9	7 -9	8
Oesophagus length	232	191 -241	219	205 - 261	229
Distance from oesophagus end to vulva				234-369	308
Distance from oesophagus end to cloaca	878	630 -938	783
Distance from vulva to anus				376 - 585	478
Mid-body diameter	50	44- 53	47	41 - 54	47
Anal/cloacal body diameter	27	24-27	26	19 -25	22
Prerectum length	68	63 - 86	72	47 - 65	56
Tail length	25	22 -25	24	106- 142	127
Spicules length (along arc)	35	34-36	35	—	—
Number of supplements	14	13 - 15	14	—	—
Supplements row length	81	73 - 86	80	—	—