Flavoperla okamotoi (Zhiltzova, 1979)

Figs. 8−18

Material examined. Russia, Far East, Sakhalinskaya Oblast, Kunashir Island: 1♂, 1♀, Valentina River, vicinity of the Tretyakovo village, 3.08.1973; 3♂, 2♀, Lesnaya River, 1 km above the confluence with the Kislaya River, 27.07.1997, coll. V. Teslenko; 1♀, Lesnaya River, vicinity of Yuzhno-Kurilsk, 11.08.1998, coll. V. Teslenko; 1♀, Tretyakovo village, 21.08.2013, coll. Yu. Sundukov.

Egg. Spindle-shaped (Figs. 8−9, 15), a length of 379–414 µm and a width at the equator of 281–287 µm (n=4). Collar is stalked and relatively high; the rim is turned down and pressed tightly against the collar wall (Figs. 8–11). Anchor has several strings with an octopus-like appearance (Figs. 8, 10, 15, 17−18); the surface of the anchor strings is unmodified, reaching 1/3 of the egg length (Figs. 8, 15). The anchor plate is densely covered with large globular bodies evenly distributed at the top (Figs. 8, 10, 17−18); the surface of the anchor plate between the cushion of globular bodies and the string bases is covered with short vertical and long horizontal rods, which are arranged in hexagonal units in 3–4 rows (Figs. 10, 17). On the extrachorionic adhesive layer of the uncleaned eggs in the shoulder area, there is a network of large hexagonal-shaped follicle cell imprints (FCIs) with distinct raised walls towards the base of the collar (Fig. 15, 17–18). Micropylar row subequatorial; orifices (> 9) are simple, much larger than the chorionic punctations (Figs. 8−9, 14) and surrounded by hexagonal rosettes, which are noticeable only on an uncleaned egg (Figs. 15−16). The chorionic surface of a cleaned egg is covered with shallow and distinct punctations throughout; pentagonal or hexagonal FCIs are weakly recognizable only on the lid (Figs. 12−13); lid rounded, and the opercular ring is raised and slightly sinuous (Figs. 8−9, 12−13, 15); the operculum line has dense and tiny punctations (Figs. 12−13).

Comments. In contrast to the Chinese species F. yangi Mo, Li & Murányi, 2021 and F. retusata Mo, Li & Wang, 2021 (Mo et al. 2021), the F. okamotoi egg is distinguished by additional anchor structures between the cushion of globular bodies and the string bases, high collar, punctured lid stripe, and operculum shape.

Distribution. East Asian insular species, whose distribution is limited by the Sakhalin and Kunashir Islands.