Nemoura jezoensis Okamoto 1922

Nemoura jezoensis (Okamoto, 1922),

(Figs. 1 ¯11)

Okamoto, 1922, Bull. Agric. Exp. Stn. Chosen, Suigen 1(1):32 Nemoura (Protonemura) jezoensis; Zhiltzova, 1982, Vest. Zool., 2: 39, fig. 2. Nemoura gracilis (description of male and female); Shimizu, 1994, Aquatic Insects 16(4):219–221(Nemoura jezoensis Okamoto, 1922 = Nemoura gracilis Zhiltzova, 1982, syn. nov.) (supplementary description of the epiproct, male and female); Kim et al., 1998, Korean J. Biol. Sci. 2(4):422 Nemoura jezoensis (new record for Korea); Zhiltzova, 2003, Fauna of Russia and Neighbouring Countries New Series No. 145:289–291, figs 483, 484 (description of male and female) Nemoura jezoensis; Bae et al., 2011 (distribution in Korea).

Material examined. RFE, Khabarovsk Region: 9 males, 1 female, 7 mature larvae, Nikolajevsky District, small unnamed creek on the shore of the Tatarsky Strait (the Sea of Japan), on the road from Lazareva Cape to Chome River, N 52°13.242' E 141°23.408', 26.06.2005, coll. K.A. Semenchenko, D. Sidorov.

Mature larvae. Body length 5.7–6.2 mm in males; 5.9–7.0 mm in females. General color brown (Fig. 2). Head with tentorial callosities contoured by narrow dark bands extending to the anterior ocellus; clypeus contoured also by a narrow dark band with mesal notch. Interocellar area with a diffuse dark patch directed towards anterior ocellus; epicranial suture pale from lateral ocelli and above compound eyes; a small dark patch below epicranial suture to the inside of each compound eye (Figs. 1, 2). Occiput with three pairs of patches surrounded by threadlike brown “loops”. Legs and cerci paler than antenna, head, pronotum, and abdomen (Fig. 2). Antenna relatively short, length does not exceed 70% of body length, scape paler than both head or pedicle and flagellum. Pronotum approximately 1.6Χ wider than long, pattern indistinct, narrow diffuse and shallow U-shaped dark brown band observing on anterior pronotal margin mesally, and merging with Х-shaped pronotal figure (Figs. 1, 2). Mesonotum and metanotum brown with diffuse pale patches. Fore femur 2.3Χ longer than wide (Fig. 6), hind femur 3.0Χ longer than wide. Abdomen relatively slender, integument light, matte in appearance, terga brown with a mesal row of darkish patches formed a longitudinal band on segments 1¯7 (Figs. 1, 2). Cerci relatively short with 24 segments; length not exceeding 80% of body length (Figs. 1, 8).

Setation. Setal fringe around the pronotum relatively regular and dense, consisting of occasional long hairs, and slender cylindrical bristles, width almost identical over the entire length, apex regularly notched (Figs. 3, 4). Length of the longest cylindrical bristles at the anterior and posterior pronotal corners attain 8.9% of pronotal width. Occasional long hairs, short club-shaped setae with irregularly notched apices, and occasional tiny procumbent setae with acute hooked apices (Figs. 3, 4) cover pronotal disc. Outer wing pad margin with cylindrical bristles with regularly notched apices; short club-shaped setae in the lines on the wing-pads (Fig. 5). Setal fringe on the outer femur margin visible, including few long, thin hairs and cylindrical bristles with regularly notched apices in regular arrangement (Figs. 1, 2, 6); the longest cylindrical bristles reach 46% of femur width on the fore leg and 42% on the hind leg. Setation of tibia features dense stout spine-shaped bristles on the inner and outer margins (Fig. 6). Terga covered with mainly short cylindrical bristles and tiny procumbent setae (Fig. 7). Along the posterior tergal margin cylindrical bristles with regular notched apices mostly long (Fig. 7); additionally, one conspicuous pair of long, thin, apically pointed bristles terminate into a very fine, thin, flexible hair, length 80-82% of segment length on terga 5¯6 (Fig. 7). Cerci with similar cylindrical bristles with regular notched apices and a few long thin hairs in the apical whorl, intercalary setation poorly developed (Figs. 9–11). Apical whorl of basal cercal segments with cylindrical bristles longer the segment; the longest of these bristles about 170% of segment’s length on cercal segment 8–9 (Fig. 9); in the apical whorl of 15–16 cercal segments the longest bristles not exceeding 97% of segment length (Fig. 10); setal ring of apical cercal segments sparse, length of a few thin hairs 46% of segment length (Fig. 11).

Diagnosis. The larvae of N. jezoensis are distinguished from other known Nemoura larvae by relatively short antenna and cerci not exceeding the body length. Marginal setation of the pronotum, outer femur, wing pads, posterior tergal margins, and apical cercal whorl, composed of cylindrical bristles, width of these uniformly throughout entire length, apices regularly notched, with the exception of the bristles on femur, these slightly narrowed at apices. Fringe on pronotal margins is regular and dense; the longest cylindrical bristles may reach 8.9% of pronotal width length. The outer femur margin bears cylindrical bristles in regular arrangement. The posterior tergal margins feature conspicuous pair of long cylindrical bristles attaining 80–82% of the segment length on terga 5¯6. Cerci have uniform setation, intercalary setation reduced: in apical whorl of basal segments the length of cylindrical bristles reaches 170% of segment’s length; in the middle part of cerci the length of bristles decreases about 97% of segment length; length few thin hairs about 46% of segment length of apical cercal segments.

Distribution. Nemoura jezoensis is an East Asian mainland-island species, inhabiting streams of Japan (Hokkaido), Korea, and RFE (Sakhalin Island, the Southern Kuril Islands (Kunashir), and shore of the Tatarsky Strait of the Sea of Japan).