Ephemera (Ephemera) transbajkalica Tshernova, 1973

Figures 16–23

Material examined. Russia: Amur Oblast, Selemdzha River basin, Burunda River, mouth, tributary of Nora River, 16.06.2004, 2♀ adults, T. Tiunova; Republic of Sakha (Yakutia), Aldan River basin, Ungra River, base of Ungrinsky reserve “Yukhta,” 01.08.2006, 2♀ adults (reared), T. Tiunova .

Distribution. East Siberia, Far East Russia, Mongolia.

The egg is oval-shaped (Figs 16–17). Dimensions: 220.0–226.0 µm in length (220.8 µm) and 123.0–129.0 µm in width (124.6 µm). The thickness of the extrachorion-adhesive layer is 1.3–1.7 µm (Figs 21, 23). The surface of the adhesive layer is slightly roughened; almost smooth (Figs 16, 18). There are one or two micropyles in the equatorial area (Figs16–17); micropyles are “tagenoform-type”; sperm guide well expressed (10.0–19.6 µm long, 4.2–7.2 µm wide), elongated, oval, with pointed distal margin, not deep (Figs 18–19). Micropylar canal: 4.0–6.0 µm long and 2.3–7.1 µm wide; weakly protrudes above the adhesive layer (Figs 16, 18). The chorionic surface is covered by the regular mesh unit’s penta- or hexagonal cells, each with a flat, almost smooth bottom and a convex protuberance in the middle (Fig. 23). The proximal part of the micropylar opening elevates above the chorion (Figs 20, 22).