Paramononchus major, Gagarin, Vladimir G. & Naumova, Tatyana V., 2016

Gagarin, Vladimir G. & Naumova, Tatyana V., 2016, Ethmolaimus riparius sp. n. and Paramononchus major sp. n. (Nematoda) from Lake Baikal, Russia, Zootaxa 4098 (3), pp. 582-592 : 587-591

Paramononchus major sp. n.

( Fig. 3 , 4 ; Table 2 )

Type material. Holotype male, slide references number 102/51, deposited in the museum collection of the Institute of Ecology and Evolution, Center for Parasitology, Russian Academy of Sciences (Moscow, Russia).

Paratypes. Six males and twelve females deposited in the collection of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences (Irkutsk, Russia).

Measurements. Table 2 .

Type locality. Bolshie Koty Bay opposite the Biological Station of Limnological Institute, Lake Baikal, Russia. Splash zone of the shore (about 50 cm above shoreline), sand. Collected on 25 June and 24 July 2010.

Etymology. The specific epithet means ”large”, “big”.

Description. Male. Body long and comparatively thin. Сuticle smooth, 8–10 µm thick at mid-body. Lips well developed. Labial region is not offset from the adjacent body. Labial and cephalic papillae conical, protruding. Cheilostom small. Stoma large and comparatively narrow. Its length 1.7–2.1 times is more than its width. Stoma walls strongly cuticularized. Stoma 1.5–1.8 times as long as labial region diameter. Large dorsal tooth located in anterior portion of stoma, its apex situated at 84–90% from base of stoma. Opposite the dorsal tooth, two longitudinal ridges are present. Two transverse ribs extend from the anterior edges of longitudinal ridges to level of dorsal tooth apex. Amphidial fovea located at the level of anterior portion of buccal cavity. Pharynx slender, muscular, comparatively long, slightly swollen proximally. Pharyngo-intestinal junction non-tuberculate. Reproductive system diorchic, testes opposed. Anterior testis straight, on the right of the intestine; posterior testis reflexed, on the right of the intestine. Spicules long, thin, ventrally curved and 2.9–3.8 times as long as cloacal body diameter as measured along the curved median line. Gubernaculum single, stick-shaped; 52–61 regularly spaced ventromedian supplements, in the form of short tubes, situated anterior to the cloaca. Tail slender, elongateconoid, curved ventrally, with 3–5 small papillae. Caudal glands well developed.

Females. General morphology similar to that of males in the structure of cuticle and anterior body end. Stoma large, its length 1.7–2.1 times is more than its width. Large dorsal tooth in anterior portion of stoma. Two longitudinal ridges are present opposite dorsal tooth. Two transverse ribs extend from the anterior edges of the longitudinal ridges to level of dorsal tooth apex. Amphidial fovea located at the base of labial region, at the level of anterior portion of buccal cavity. Pharynx slender, muscular, comparatively long, slightly swollen proximally. Rectum 0.6–0.9 times as long as anal body diameter. Reproductive system didelphic, amphidelphic. Ovaries reflexed, tips generally not reaching the uterus-oviduct junction. Anterior ovary on right side and posterior ovary on left side of intestine. Terminal zone of oogonia arranged in one or two rows; growth zone with a single row of gradually enlarging oocytes. Vagina with muscular walls, occupying 36–45% of the corresponding body width. Uterus spacious, filled with small rounded spermatozoa and containing 1– 4 eggs measuring 121–170 x 112–135 µm. Vulva a transverse slit, situated slightly posterior to mid-body. Vulval lips slightly protruding outside the body contour. Tail elongate-conoid, slightly curved ventrally. Caudal papillae absent. Caudal glands and spinneret present.

Diagnosis. Body 6120–6940 µm long in males, 5926–7820 µm long in females. Cuticle smooth. Labial and cervical sensillae in the shape of papillae. Buccal cavity large, 97–120 µm long and 52–63 µm wide. Dorsal tooth large, its apex situated at 84–90% from base of buccal cavity. Opposite dorsal tooth two longitudinal ridges are present. Two transverse ribs extend from anterior edges of longitudinal ridges to level of dorsal tooth apex. Stoma 1.5–1.9 times as long as labial region diameter. Uterus spacious, containing one to four eggs measuring 121–170 x 112–135 µm. Spicules 410–475 µm long, thin, curved ventrally. Gubernaculum single, stick-shaped. Precloacal supplements in the shape of short tubes, 52–61 in number, regularly spaced.

Differential diagnosis. Paramononchus major sp. n. is the largest species of the genus Paramononchus . It is closest in body size to P. orientalis Gagarin & Naumova, 2012 , but differs by being even longer (L = 5926–7820 µm vs L = 3081–3778 µm in P. orientalis ), having longer spicules (410–475 µm vs 208–238 µm long in P.

orientalis ) and a greater number of male precloacal supplements (52–61 vs 21–24 in P. orientalis ) ( Gagarin & Naumova 2012c).

At present, the genus Paramononchus Mulvey, 1978 includes 6 valid species: P. arcticus Mulvey, 1978 ; P. alimovi Tsalolikhin, 1990 , P. thiocrenobius ( Soos, 1943) (cyt. Pax & Soós, 1943), P. baikalensis Gagarin & Naumova, 2010 , P. orientalis Gagarin & Naumova, 2012 and P. m aj or sp. n. ( Gagarin & Naumova 2012c, present article). Three species are found in Lake Baikal: P. baikalensis , P. orientalis , and P. major sp. n.

A key for the identification of valid species of the genus Paramononchus is given below.

Figures

FIGURE 3. Paramononchus major sp. n. Holotype male and paratype female. A: male, entire body; B: vulva region; C: male head; D: female tail; E: male, posterior body end. Scale bars: A— 400 µm; E— 200 µm; B, D— 100 µm; C— 70 µm.

FIGURE 4. Paramononchus major sp. n. Holotype male and paratype female. A: male, entire body; B: female, entire body; C, E: male head; D: female head; F: vulva region; G: cloaca region; H: male, posterior body end; I: female tail. Scale bars: A, B— 500 µm; H— 100 µm; F, G, I— 50 µm; C – E— 20 µm.

Tables

TABLE 2. Morphometrics of Paramonchus major sp. n. (all measurements are given in µm, except for the ratios a, b, c, c', V; length of the stoma divided by labial region diameter; number of supplements).

Character Holotype male	Paratype males (n = 6)	Paratype females (n = 13)
	range mean	range mean
L 6307	6120–6940 6477	5926–7820 6938
a 40	35–46 37	36–50 40
b 4.3	3.8–4.3 4.1	3.4–4.1 3.8
c 25	25–35 28	20–31 22
c' 1.8	1.6–2.0 1.8	2.1–3.2 2.7
V, % –	– –	59.4–62.8 61.1
body diameter at the level of cephalic setae 70	62–85 70	70–83 76
mid-body diameter 168	168–200 180	142–200 175
anal or cloacal body diameter 150	122–150 135	100–145 118
stoma length 102	102–112 106	95–120 108
length of the stoma divided by labial region diameter 1.8	1.7–2.1 1.9	1.7–2.2 2.0
pharyngeal length 1470	1468–1650 1599	1520–2100 1813
distance from the pharynx base to the cloaca 4575	4260–5130 4640	– –
distance from the pharynx base to the vulva –	– –	1988–2800 2429
distance from the vulva to the anus –	– –	2088–2700 2381
spicula length along the arc 427	410–475 437	– –
gubernaculum length 120	88–125 102	– –
number of supplements 58	52–61 56	– –
length of supplement row 430	412–525 459	– –
stoma length 262	192–288 238	230–392 315