Rhyacophila yukii Tsuda 1942

Torii, Takaaki & Kobayashi, Tohru, 2021, Redescription of Rhyacophila yukii Tsuda 1942 and description of three new Rhyacophila species from Japan (Trichoptera: Rhyacophilidae), Zootaxa 4995 (3), pp. 537-550 : 538-540

Rhyacophila yukii Tsuda 1942

Figs 1A–1I

Rhyacophila yukii Tsuda 1942, pp. 248–249 , fig. 7, male; Hattori 2005, pp. 427, 435, fig. 6, male from original description; Inazu and Nishida 2011, p. 176, fig. 20, male; Kawase et al. 2017, p. 25, list; Hattori 2018, pp. 487, 495, fig. 5, male from original description.

Material. 11 males, Ojigahata, Taga-cho, Inukami-gun , Shiga (35.2030°N, 136.4108°E, 654 m a.s.l.), 11.v.2008, H. Morita (2 males: SEHU, 9 males: CBM); 1 male, Shiratani, Makino-cho, Takashima-shi, Shiga, 17.v.2014, S. Takeda ( NKW) .

Male. Length of each forewing 6.5–8.0 mm (n = 13); specimens in alcohol with head, thorax, and wings dark brown; legs yellowish brown, with spurs dark brown.

Male genitalia ( Figs 1A–1I ). Segment IX in lateral view subrectangular, with upper portion longer than lower portion; rectangular in dorsal view, twice as wide as long. Segment X in lateral view rod-shaped, tapered and slightly hooked ventrad at tip, variably trapezoid to triangular in dorsal view ( Figs 1B, 1C ), approximately triangular in diagonally above of caudal view, slightly bends downward at apex, 1.2–1.3 times as wide as long. Apical band (a.b.) in lateral view long and narrow, bar shaped. Dorsal branch of aedeagus (d.b.a.) in lateral view slightly protruding. Ventral branch of aedeagus (v.b.a.) in lateral view cylindrical and protruding. Aedeagus (aed.) in lateral view broadly curved 90° like long and narrow spine. Ventral lobe of aedeagus (v.l.a.) elongate subelliptical in dorsal view. Basal segment of each inferior appendage (b.i.a.) nearly rectangular in lateral view, in ventral view with its mesal margin concave and lateral margin straight; apical segment of each inferior appendage (a.i.a.) in lateral view with apex depressed obliquely, in ventral view with mesal and lateral margins straight.

Female. Unknown.

Immature stages. Unknown.

Distribution. Japan (Honshu).

Remarks. This species belongs in the Rhyacophila sibirica Group of Schmid (1970). Tsuda (1942) described it based on one male collected from Ohmiya-gawa, Hiei-zan, Shiga Prefecture, central Japan. The specimens in this study are from “Ojigahata, Taga-cho, Inukami-gun, Shiga,” which is 56 km northeast in a straight line from the type locality. His description and illustrations of segment X and other characters of the male genitalia ( Figs 1H, 1I ) agree with those of males examined in this study ( Figs 1A, 1B, 1C ). Tsuda (1942) described segment X of his male as approximately triangular and tapering to apex in dorsal view. Segment X of our specimens are triangular to trapezoidal in dorsal view but appears to be triangular and directed diagonally upward in caudal view; the morphology of segment X in dorsal view is slightly variable ( Fig. 1C ). It is necessary to be careful about the angle of observation to observe the variety of shape of segment X.

Tsuda (1942) reported that the type specimen of R. yukii was stored at Kyoto Imperial University (Kyoto University). The Tsuda collection was acquired later by the Osaka Museum of Natural History , but now the type specimen of this species cannot be found ( Tanida per. com.). Since it could not be confirmed whether the type specimen has completely disappeared, we do not specify neotype specimens here .

In addition, examination of the specimen of R. yukii reported from Mt. Sentsu-zan, Okuizumio-cho, Shimane Prefecture, by Kawase and Hayashi (2010) showed that the shape of the tip of male segment X did not agree with the original description and their specimen possibly actually is an example of an undescribed species. Whether this specimen is an intraspecific variant or a different species still needs further consideration.

Figures

FIGURES 1A−1I. Rhyacophila yukii Tsuda 1942, male genitalia (1A−1I): 1A, left lateral; 1B, segment X, dorsal; 1C, segment X, caudal (variation from same locality); 1D, ventral lobe of aedeagus, dorsal; 1E, segment IX and inferior appendages, ventral; 1F, phallic apparatus, left lateral; 1G, caudal; 1H, left lateral, by Tsuda (1942); 1I, dorsal, by Tsuda (1942). Abbreviations: a.b. = apical band; aed. = aedeagus; a.i.a. = apical segment of an inferior appendage (paired); b.i.a. = basal segment of an inferior appendage (paired); d.b.a.= dorsal branch of aedeagus; pht. = phallotheca; v.b.a. = ventral branch of aedeagus; v.l.a. = ventral lobe of aedeagus.