Hydroptila nago Ito sp. nov.

(Fig. 1)

Hydroptila sp.: Ito, 2015, 15, Okinawa-jima.

Diagnosis. The male of this species is similar to that of Hydroptila dorsoprocessuata Botosaneanu 1993, known in eastern Russia, in having a long dorsal process on segment IX, an elongate-rectangular semi-membranous dorsal plate, and long triangular inferior appendages. However, H. nago is clearly discriminated from H. dorsoprocessuata as follows: The aedeagus is bifurcate in H. nago but single in H. dorsoprocessuata; and in lateral view, the subgenital plate is extended caudad to near the tip of the inferior appendages in H. nago, but is relatively short, reaching only to the middle of the inferior appendages in H. dorsoprocessuata.

Description. Male. Wings brown in alcohol. Forewings each 1.6–1.9 mm long, hind wings each 1.2–1.3 mm long (n = 2). Antennae brown, 1.2–1.3 mm long, 21–23-segmented (n = 2). Short ventromesal process on abdominal segment VII.

Male genitalia (Figs 1 A–1E). Segment IX moderately long with anterior margin produced into long dorsal process (d.pr.) at middle of posterior margin in lateral and dorsal views. Dorsal plate (d.pl.) mostly membranous, elongate-rectangular with shallow middle apical excavation in dorsal view. Subgenital plate (s.pl.) subrectangular in basal half in ventral view, abruptly produced distally in long bar with apical seta. Inferior appendages (i.a.) long without any lobes, rod-like in lateral view, long-triangular in ventral view. Phallic apparatus with short titillator (ti.) at basal 1/3, aedeagus (ae.) and sclerotized sclerotized extension of ejaculatory duct (ej.du.) directed caudad, almost straight; aedeagus bifurcate, each half acute apically.

Female. Unknown.

Holotype. Male, Japan, Ryukyu, Okinawa-jima, Nago-shi, Genka, Genka-gawa, Hogen-hashi (26.6292 N, 128.0847 E, 90 m above sea level, 8.iv.2011, T. Ito, light trap (CBM-ZI 167018).

Paratype. 1 male, type locality, 17–19.x.2014, T. Ito, light pan trap (CBM-ZI 167019).

Etymology. The name “ nago ” is a noun in apposition, coined from the type locality.

Distribution. Japan (Ryukyu: Okinawa-jima).

Remarks. The adults of this species were collected near fast-flowing rivers with stony substrates.

Japanese name. Nago-hime-tobikera.