Isoperla mongolica Zhiltzova 1972

Isoperla mongolica Zhiltzova, 1972 Figs. 56–62 Material examined: Russia, Siberia, Krasnojarsky Krai, Khakassia: 1♀, 50 km NW of Shira Lake, Black Iyus River, 4.07.2014, coll. A. Leley; Transbaikalia: 1♂, Rastorguikha River, Selenga R. Basin, Burkalsky protected area, 23.08.2018, coll. Matafonoff; Altai Republic: 1♂, 1♀, Tuekta River, Ob River basin, 05.09.2021, coll. L. Yanygina. Mongolia, Arkhangai Aimak, Onder-Ulaan, Tsakhir: 2♀, Cenlnt gol. 48° 07 N 100 °22 E, 2100 m above sea level, 10– 13.05.1997, coll. Yu. Marusik. Egg. Shape oval, marginally asymmetrical with posterior pole narrower than anterior pole, anterior pole widely rounded, cross-section concave (Figs. 56, 59). Length 229‒260 µm, width at the equatorial region 175‒182 µm (n=4). Collar well developed, elevated with irregular longitudinal ridges; base of collar deeply embedded and surrounded by a narrow smooth shoulder; rim flanged and wavy apically (Figs. 56, 58–59). Anchor mushroom-shaped, with small globular bodies concentrated into groups of 2–5 located mainly in a peripheral area along the anchor edge (Fig. 57). Follicular cells near the collar ranged from pentagonal to hexagonal (Fig. 56). Chorion covered with hexagonal FCIs with thickened, slightly elevated ridges and numerous (12–20) deep pits (Figs. 60‒62). Micropyles positioned singularly along one row on follicle cell ridges near the anterior ⅓ (Fig. 60). Orifices set in small, oval, cup-like depressions; sperm guides tunnel-shaped and relatively long and wider than ridges and are associated with FCI rosettes (Figs. 56, 60–62). Eclosion line absent. Distribution. East Palaearctic species originally described from Mongolia (Onon River basin). The species is also known from Russia in the rivers of East and West Siberia, including Altai, the Baikal Reserve, and the Selenga River Basin. East Kazakhstan (Devyatkov 2022). Remarks. The original description clearly indicates the size and shape of the egg, as well as the chorion structure with deep, large pits and their unclear location in polygonal fields (Zwick & Surenkhorloo 2005). The collar and anchor were also described, which generally corresponds to the SEM results presented here.