Mononchus minutus, Naumova & Gagarin, 2018

Naumova, Tatyana V. & Gagarin, Vladimir G., 2018, Prodorylaimus baikalensis sp. n. and Mononchus minutus sp. n. (Nematoda) from Lake Baikal, Russia, Zootaxa 4459 (3), pp. 525-534 : 530-533

Mononchus minutus sp. n.

( Figs 3 , 4 ; Table 2)

Type material. HOlOtype male, slide reference number 102/66, 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 2.

Type locality. Lake Baikal , Siberia , Russia, AJa Bay, depth 40–80 m, silt. COllected On 23 August 2017.

Etymology. The specific epithet means “small, minute”.

Description. Male. BOdy cOmparatively shOrt and thin. Cuticle smOOth, 3–4 µm thick at mid-bOdy. Lips well develOped, angular. Labial regiOn Offset frOm the adJacent bOdy. Labial and cephalic papillae cOnical. CheilOstOm small. Buccal cavity large and cOmparatively narrOw. Its length 2.3–2.5 times is mOre than its width. StOma walls strOngly cuticulariZed. StOma 1.8–2.2 times as lOng as labial regiOn diameter. Large dOrsal tOOth lOcated in anteriOr pOrtiOn Of buccal cavity, in apeX situated at 86–91% frOm base Of buccal cavity. A shOrt transverse rib situated OppOsite the dOrsal tOOth. Amphidial fOvea lOcated at the level Of anteriOr pOrtiOn Of buccal cavity. PharynX slender, muscular, cOmparatively lOng, slightly swOllen prOXimally. PharynX-intestinal JunctiOn nOn-tuberculate. Caudal glands cOmparatively large, rOund. ReprOductive system diOrchic, testes OppOsed. AnteriOr testis straight, On the right Of the right Of the intestine, pOsteriOr testis refleXed, On the right Of the intestine. Spicules lOng, thin, ventrally curved and 2.8–3.8 times as lOng as clOacal bOdy width as measured alOng the curved median line. Gubernaculum stick-shaped. AnteriOr tO clOaca are 21–25 regularly spaced ventrOmedian supplements in the fOrm Of shOrt tubes. Tail slender, elOngate-cOnical, slightly curved ventrally. Tail terminus swOllen. Caudal gland and spinneret well

Female. General mOrphOlOgy is similar tO that Of males in structure Of cuticle and anteriOr bOdy end. Cuticle smOOth. Buccal cavity large, its length 2.1–2.4 times its width. Large dOrsal tOOth in anteriOr pOrtiOn, with shOrt transverse rib situated OppOsite. 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. Caudal glands large, rOund. Rectum 0.7–1.1 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 Of 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 slightly muscular walls, Occupying 30–45% Of cOrrespOnding bOdy width. Uterus spaciOus, filled with small rOunded spermatOZOa and cOntaining 1– 2 eggs measuring 150–182 X 63 – 78 µm. Vulva a transverse slit, situated slightly pOsteriOr tO mid-bOdy. Vulval lips unsclerOtiZed and slightly prOtruding Outside the bOdy cOntOur. Tail elOngate-cOnical, slightly curved ventrally. Tail terminus swOllen. Caudal glands and spinneret present.

Diagnosis. BOdy 2337–2825 µm lOng in males, 2380–2893 µm lOng in females. Cuticle smOOth. Labial and cephalic setae in the shape Of papillae. Buccal cavity large and cOmparatively narrOw, 64–74 µm lOng and 28–31 µm wide. DOrsal tOOth large, its apeX situated at 86–91% frOm base Of buccal cavity. OppOsite dOrsal tOOth situated shOrt transverse rib. StOma 1.8–2.2 times as lOng as labial regiOn diameter. PharynX muscular, cOmparatively lOng. PharynX- intestinal JunctiOn nOn-tuberculate. Cardial glands large, rOund. Vulva a transverse slit, situated slightly pOsteriOr tO mid-bOdy. Uterus spaciOus, cOntaining One Or twO eggs measuring 150–182 X 63 –78 µm. Spicules 205– 215 µm lOng, thin, curved ventrally. Gubernaculum stick-shaped. PreclOacal supplements 21–25 in number, regularly spaced. Tail slender, elOngate-cOnical, slightly curved ventrally.

Differential diagnosis. Mononchus minutus sp. n. is mOrphOlOgically clOse tO M. niddensis Skwarra, 1921 and M. agilis Gagarin & MataphOnOv, 2004 . FrOm the fOrmer species it differs in the shOrter bOdy (L = 2337–2893 µm vs. L = 2.8–3.5 µm in M. niddensis ), cOmparatively less slender tail in females (cʹ = 3.3–4.4 vs. cʹ = 7–8 in M. niddensis ), larger buccal cavity (measuring 64– 74 X 28–31 µm vs. measuring 46– 56 X 20–25 µm in M. niddensis ), lOnger spicules (205–215 µm lOng vs. 134–140 µm in M. niddensis ) and smaller number Of ventrOmedian supplements in males (21–25 in number vs. 26–32 in number in M. niddensis ) ( Andrássy 2009). FrOm M. agilis it differs in the shOrter bOdy (L = 2337–2893 µm vs. L = 2877–3209 µm in M. agilis ), thinner bOdy (a = 25–33 vs. a = 17–25 in M. agilis ), cOmparatively shOrter tail in females (c = 12.8–15.1 vs. c = 9.8–11.6 in M. agilis ), lOnger spicules (205–215 µm lOng vs. 186–192 µm lOng in M. agilis ) and smaller number Of ventrOmedian supplements in males (21–25 in number vs. 30–31 in M. agilis ) ( Gagarin & MataphOnOv 2004).

Figures

FIGURE 3. Mononchus minutus sp. n., holotype male and paratype female. A: male head; B: female, vulva region; C: female tail; D: male, anterior body end; E: male, posterior body end. Scale bars: A—40 µm; C—50 µm; E—70 µm; B—100 µm; D— 150 µm.

FIGURE 4. Mononchus minutus 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, G: female, vulva region; H: male, cloaca region; I: male, posterior body end; J: female tail. Scale bars: A—500 µm; B—200 µm; C—100 µm; F, G, I, J—50 µm; D, E, H—20 µm.