Prodorylaimus baikalensis sp. n. and Mononchus minutus sp. n. (Nematoda) from Lake Baikal, Russia Author Naumova, Tatyana V. Author Gagarin, Vladimir G. text Zootaxa 2018 2018-08-16 4459 3 525 534 journal article 29011 10.11646/zootaxa.4459.3.6 2153e409-f93c-49f1-af25-7960c68181b1 1175-5326 1458871 C9FCF1DF-B95C-4270-8E20-62C02F009127 Prodorylaimus baikalensis sp. n. ( Figs 1 , 2 ; Table 1 ) Type material . HOlOtype male, slide reference number 102/65, depOsited in the HelminthOlOgical Museum Of the Russian Academy Of Sciences ( RAS ), Institute Of EcOlOgy and EvOlutiOn, Center fOr ParasitOlOgy RAS ( MOscOw , Russia ). Paratypes . DepOsited in the cOllectiOn Of the LimnOlOgical Institute , Siberian Branch Of the Russian Academy Of Sciences ( Irkutsk , Russia ). Measurements . Table 1 . Type locality. Lake Baikal , Siberia , Russia , AJa Bay , depth 40–80 m , silt. COllected On 23 August 2017 . Etymology . The specific epithet means “frOm Lake Baikal”. TABLE 1. Morphometrics of Prodorylaimus baikalensis sp. n.

Character	Holotype male	Paratype males (n = 4)	Paratype females (n = 11)
L	1847	1875±98 (1760–1995)	1749±120 (1555–1956)
a	39	38±5 (31–42)	35±4 (30–41)
b	4.4	4.5±0.4 (4.2–5.1)	4.0±0.3 (3.2–4.3)
c	14.5	16.2±1.6 (14.5–17.6)	16.3±1.4 (13.9–18.5)
cʹ	3.8	3.6±0.2 (3.3–3.9)	4.3±0.5 (3.8–5.5)
U (%)	–	–	51.5±1.5 (49.5–54.4)
Body diameter at level of cephalic sensillae, in µm	15	15±1 (14–16)	15±1 (14–17)
Mid-body diameter, in µm	48	50±10 (43–65)	51±5 (40–60)
Anal or cloacal body diameter, in µm	33	33±2 (30–35)	25±2 (22–28)
Odontostyle length, in µm	27	27±3 (25–31)	26±1 (25–30)
Odontostyle length divided by labial region diameter	1.8	1.7±0.1 (1.6–1.8)	1.7±0.1 (1.5–1.8)
Odontophore length, in µm	20	21±1 (20–23)	18±2 (16–22)
Pharynx length, in µm	420	428±19 (405–450)	436±33 (400–513)
Distance from the pharynx base to the cloaca, in µm	1300	1322±83 (1225–1425)	–
Distance from the pharynx base to the vulva, in µm	–	–	463±59 (320–545)
Vulva-anus distance, in µm	–	739±62 (643–818)
Tail length, in µm	127	117±14 (100–130)	108±11 (95–138)
Tail length divided by vulva-anus distance	–	6.8±0.8 (6.4–7.3)
Prerectum length, in µm	155	171±23 (150–192)	86±13 (68–110)
Prerectum length divided by anal or cloacal diameter	4.7	4.6±0.5 (4.5–5.2)	3.4±0.4 (3.1–3.9)
Spicula length measuring along the horda, in µm	46	50±4 (46–55)	–
Spicula length divided by cloacal diameter	1.4	1.6±0.1 (1.4–1.7)	–
Lateral guiding pieces length, in µm	8.0	7.5±0.2 (7.0–8.0)	–
Number of supplements	20	20±3 (18–24)	–
Length of the supplement row, in µm	165	196±24 (165–220)	–

FIGURE 1. Prodorylaimus baikalensis sp. n. , holotype male and paratype female. A: male head; B: male, anterior body end; C: female, vulva region; D: female, posterior body end; E: male posterior body end. Scale bars: A—15 µm; D, E—40 µm; C— 50 µm; B—100 µm. FIGURE 2. Prodorylaimus baikalensis sp. n. , holotype male and paratype female. A: male, entire body; B: female, entire body; C: male, anterior body end; D: male head; E: female head; F: female, vulva region; G: female tail; H: male, supplement row; I: male tail; J: mail, cloaca region. Scale bars: A, B—200 µm; C—50 µm; F—J—20 µm; D, E—10 µm. Description. Male. BOdy average siZe, cOmparatively thin and with rather shOrt tail. Cuticle smOOth under light micrOscOpe, 2.5–3.0 µm thick at mid-bOdy. Lateral pOres nOt visible. Lips well develOped; labial papillae distinct. Labial regiOn Offset frOm the adJacent bOdy. Amphidial fOvea cup-like, wide, Occupying 60–65% Of the cOrrespOnding bOdy diameter and situated at the base Of lips. OdOntOstyle straight and slender, 1.6–1.8 times the labial regiOn diameter, its aperture cOnstituting 27–30% Of its length. OdOntOphOre rOd-like, 0.6–0.8 times as lOng as OdOntOstyle. Guiding ring dOuble, thick. PharynX muscular, eXpanding gradually alOng its whOle length. Pharyngeal gland nuclei indistinct. Cardia cOnOid, muscular, surrOunded with intestinal tissue. Testes paired, OppOsed. Spicules dOrylaimOid, 1.4–1.7 clOacal bOdy diameters lOng, with twO spindle-shaped lateral guiding pieces. An additiOn tO the adanal pair, a series Of 17–23 cOntiguOus ventrOmedian supplements are present. Prerectum lOng, 4.5–5.2 clOacal bOdy diameters lOng, intestine-prerectum JunctiOn is lOcated in the regiOn Of supplement series. Tail elOngate-cOnical, distal end pOinted. Female . General mOrphOlOgy similar tO that Of males in structure Of cuticle and anteriOr bOdy end. Cuticle smOOth. Lips well develOped. Labial regiOn Offset frOm the adJacent bOdy. Amphidial fOvea cup-like, wide, situated at the base Of lips. OdOntOstyle straight and slender, 1.5–1.8 times the labial regiOn diameter. OdOntOphOre rOd-like, 0.5–0.9 times as lOng as OdOntOstyle. Guiding ring dOuble, thick. PharynX muscular, eXpanding gradually alOng its length. Pharyngeal gland nuclei indistinct. Prerectum 3.1–3.9 anal bOdy diameter lOng. Rectum 1.2–1.5 times as lOng as anal bOdy diameter. ReprOductive system didelphic, amphidelphic. Vulval lips nOt sclerOtiZed, nOt prOtruding Outside the bOdy cOntOur. Ovaries relatively shOrt. OOcytes numerOus, first in twO rOws, then in a single rOw. Uterus spaciOus, with spindle-shaped spermatOZOa. Uterus cOntaining One Or twO eggs measuring 95–100 X 33 –38 µm. Vagina eXtending inwards tO half the cOrrespOnding bOdy diameter. Pars proximalis vaginae with straight walls, 38–50 µm lOng; pars refringens vaginae cOnsisting Of twO drOp-like sclerOtiZatiOns; pars distalis vaginae shOrt, with rOunded walls. Vulva a transverse slit. Distance frOm vulva tO anus 5.9–7.0 times as lOng as tail length. Tail elOngate-cOnical, its distal end pOinted. Diagnosis . BOdy average siZe and cOmparatively thin ( L = 1760–1995 µm, a = 31–42 in males; L = 1555–1956 µm, a = 30–41 in females). Cuticle smOOth. Labial regiOn Offset frOm the adJacent bOdy. OdOntOstyle straight and slender, 25–30 µm lOng; its aperture cOnstituting 27–30% its length. OdOntOphOre 16–23 µm lOng. Guiding ring dOuble and thick. PharynX muscular, eXpanding gradually alOng its whOle length. Vulva a transverse slit. Distance frOm vulva tO anus 5.9–7.0 times as lOng as tail length. Uterus spaciOus, with numerOus spermatOZOa and 1– 2 eggs , measuring 95–100 X 33 –38 µm. Spicules 46–55 µm lOng; 18–24 ventrOmedian supplements (adanal pair and rOw Of 17–23 cOntiguOus supplements). Prerectum in males lOng, well develOped, 4.5–5.2 clOacal bOdy diameters lOng, intestine-prerectum JunctiOn is lOcated in the regiOn Of supplement series. Tail elOngate-cOnical, cOmparatively shOrt ( c =14.5–17.6, cʹ = 3.3–3.8 in males; c = 13.9–18.5, cʹ = 3.8–5.5 in females). Differential diagnosis . The genus Prodorylaimus includes 24 valid species ( Vinciguerra & Orselli 2011 , Gagarin & NaumOva 2011 , Gagarin & NaumOva, 2015 ). Prodorylaimus baikalensis sp. n. is similar tO P. irminii Vinciguerra & Orselli, 2011 and P. obesus Ahmad & JairaJpuri, 1982 . FrOm the fOrmer species it differs in shOrter bOdy ( L = 1555–1995 µm vs. L = 1850–2500 µm in P. irminii ) and relatively thicker bOdy ( a = 30–42 vs. a = 48–68 in P. irminii ), relatively lOnger tail ( c = 13.9–18.5 vs. c = 18.8–37.3 in P. irminii ), lOnger OdOntOstyle (25.6–31.0 µm lOng vs. 19.5–25.0 µm lOng in P. irminii ), great number Of ventrOmedian supplements ( 18–24 in number vs. 15–16 in number in P. irminii ) ( Vinciguerra & Orselli 2011 ). FrOm P. obesus in differs in the lOnger and slender tail (c = 13.9–18.5, cʹ = 3.3–5.5 vs. c = 26–30, cʹ = 2 in P. obesus ), greater number Of ventrOmedian supplements ( 18–24 in number vs. 15–18 in number in P. obesus ), shOrter OdOntOphOre (16–23 µm lOng vs. 32–33 µm lOng in P. obesus ) and lOnger prerectum (females 68–110 µm lOng, males 150–192 µm lOng vs. females 55–69 µm lOng, males 98– 124 µm lOng in P. obesus ( Ahmad & JairaJpuri 1982 ) .