Isoperla altaica Samal 1939

Isoperla altaica Šámal, 1939 Figs. 1‒9 Material examined. Russia, Siberia: Krasnoyarsk Krai, Khakassia: 3♀, 22 km NW of Shira Lake, Bely Iyus River, 2.07.2014, coll. A. Leley; 1♂, Rastorguikha River, Selenga R. Basin, Burkalsky protected area, 23.08.2018, coll. Matafonoff; 1♂ 1♀, Altai, Tuekta River, 05.09.2021, coll. L. Yanygina. Egg. Shape oval, symmetrical, with anterior and posterior poles broadly rounded and a concave cross-section (Figs. 5‒6). Length 322–332, width at the equator of 234–239 µm (n=2). Collar well developed, with raised longitudinal wavy carinae and small transverse projections (Figs. 1, 3); base with a thickened, wavy ridge wider than the apically flanged rim, so the collar appears multi-leveled from above (Figs. 1, 3, 5). Anchor mushroom-shaped, with small globular bodies concentrated into groups of five and located in a peripheral area along the anchor edge; top of the anchor deeply embedded (Figs. 2, 4). Follicle cell impressions (FCIs) near the collar range from elongated to hexagonal (Figs. 1–2, 5). Chorion covered with hexagonal FSCs with slightly thickened elevated ridges (Figs. 1‒2, 5–8); floors shallow with numerous (20) shallow pits (Figs. 1‒2, 5–8). Micropyles arranged singularly in a row on follicle cell ridges near the anterior ¼ of the egg (Figs. 1‒2, 6). Orifices oval and located on raised, tunnel-shaped, and relatively long sperm guides, some associated with FCI rosettes (Figs. 7–8). Eclosion line absent. The chorionic structure on an external membrane comprises hexagonal FCIs bearing scattered adhesive mushroom bodies along the perimeter of each cell (Fig. 9). Distribution: East Palaearctic species with limited distribution in Russia, Siberia: Altai, Sayan, Transbaikalia. East Kazakhstan. Mongolia. Remarks. Isoperla altaica eggs from Siberia are smaller in size than those from Mongolia (360×250 µm) and larger than those from East Kazakhstan (295×235 µm) (Zwick & Surenkhorloo 2005). Apparently, the Siberian eggs imaged here are quite mature since their chorion is completely covered by FCIs. According to the available data obtained in transmitted light, the structure of the eggs from Kazakhstan is finely punctured, whereas the chorion of Mongolian eggs is unstructured (Zwick & Surenkhorloo 2005).