Rhyacophila imakane Ito & Kuhara, 2024

Ito, Tomiko, Kuhara, Naotoshi & Malicky, Hans, 2024, Five new species of the genus Rhyacophila Stephens (Trichoptera, Rhyacophilidae) from southwestern Hokkaido, northern Japan, Zootaxa 5536 (4), pp. 551-568 : 559-561

Rhyacophila imakane Ito & Kuhara sp. nov.

( Figs 1D , 4A–4I )

Rhyacophila sp. 6 : Ito et al. 2010, pp. 56, 81, Hokkaido (Shiribeshi, Oshima).

Species group and diagnosis. This new species belongs to the Rhyacophila kaltatica Species Group, with the male having the dorsal posterior margin of segment IX protruding caudad with several spiny processes, a long depressed segment X, a large sclerotized anal sclerite and thick inferior appendages with long basal and short apical segments. The male of R. imakane sp. nov. resembles those of R. hamata and two new species described in this study, R. bifue sp. nov. and R. misago sp. nov. However, the male of R. imakane is clearly distinguished from the latter two species by a pair of slender curved processes arising from the rugged area of segment IX and the position of the acute dorsomesal process of each inferior appendage which arises from the middle of the dorsomesal edge of the basal segment.

The female of this new species is also similar to those of R. hamata , R. bifue , and R. misago , but can be readily discriminated from those of the latter by the deep sinuous posterolateral margins of segment VIII and the deep and wide incision of ventroposterior margin of the segment.

Adult. Male: Each forewing 6.8–7.4 mm long (mean = 7.1 mm, n = 5) and each hind wing 6.2–6.7 mm (mean = 6.5 mm, n = 5). Female: Each forewing 7.7–8.1 mm (mean = 7.9 mm, n = 5) and each hind wing 6.8–7.3 mm (mean = 7.0 mm, n = 5). Head dark brown, warts light brown with brown setae, antennae dark brown, palpi light brown. Thorax dark brown dorsally. Legs light brown with dark brown spurs. Wings brown with darker veins and fulvous pterostigma. Abdomen with dark brown tergites and light brown sternites, dark pigments scattered dorsally; scent glands of sternite V opening on anterolateral-angle mounds well encircled by sutures; small mid-ventral process on each of sternites VI and VII in male and on sternite VI in female.

Male genitalia ( Figs 4A–4D ). Dorsal margin of segment IX (IX) about 3 times as long as ventral margin in lateral view. Rugged posterior area of segment IX (ru po IX) with several short acute processes and pair of slender curved processes (sl cu pr) laterally; additionally, short slender curved process on one side in few specimens (arrow in Fig. 4B ). Segment X (X) depressed; long board-like, widened apically in dorsal view; long bar-like, directed caudad in basal 4/5, curved dorsad in apical 1/5 with subacute apices in lateral view. Anal sclerite (an sc) strongly sclerotized; semicircular with shallow middle incision in dorsal view; subtriangular with large subquadrate process basally in lateral view. Tergal strap indistinct, apical band (ap ba) short, curved in lateral view. Aedeagus (ae) long, slender. Parameres absent.

Basal segment of each inferior appendage (b inf app) long, 2 times as long as apical segment (a inf app), dorsal and ventral margins parallel with each other in lateral view; dorsomesal process (do me pr) arising from middle of dorsomesal edge of basal segment, gradually narrowing, directed ventromesad basally, then curved dorsoposterad, acute apically; apical segment of each inferior appendage (a inf app) large subquadrate in lateral view, oblong in dorsal and ventral views, mesal surface of apical part with numerous spinules.

Female genitalia ( Figs 4E–4I ). Segment VIII (VIII) relatively short, 0.9 times as long as basal height, slightly narrowing posteriorly; posterior margin sinuous in lateral view, widely convex in dorsal view, deeply and widely incised in ventral view.Vaginal apparatus long; processus spermathecae (ps) round in ventral view, semi-membranous; posterior process (pp) sclerotized, long, 2 times as long as processus spermathecae, subacute apically.

Larva. Unknown.

Holotype. Male, Hokkaido, Hiyama, Imakane-chô , Ôshubunnai-no-taki (42.3938°N, 140.1831°E, 100 m a.s.l.), 5.viii.2006, leg. TI & TH, S ( CBM-ZI 0189175 ).

Paratypes. 9 males, 3 females, same data as holotype ( SPMN-IS) .

Other specimens. Hokkaido, Shiribeshi: Shimamaki-mura , Nagumo-no-sawa, upper reach, 10 males, 5 females, 21.v–20.vi.2007, leg. TI , S ( SPMN-IS). Iburi: Sôbetsu-chô, Benkei , small stream, 12 males, 11 females, 25.vi.2011, leg. NK , M ( NK); 7 males, 2 females, 14.vii.2011, leg. NK , M ( NK); 3 males, 3 females, 31.vii.2011, leg. NK , M ( NK); 2 males, 5 females, 13.viii.2011, leg. NK , M ( NK). Hiyama: Imakane-chô , Ôshubunnai-no-taki (type locality), 2 males, 1 female, 5.viii.2006, leg. TI & TH, S ( TI).

Distribution ( Fig. 1D , black triangles). Hokkaido (southwestern area).

Habitat. Adults of this species were collected in mountain areas beside waterfalls and small rapid streams.

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

Japanese name. Imakane-nagare-tobikera.

Figures

FIGURE 1. Recorded collection sites of Rhyacophila species. 1A, location of Hokkaido and recorded sites of known species discussed in present study. 1B–1E, recorded and collected sites in Hokkaido: 1B, 1C, R. eniwa sp. nov. and R. arefini Lukyanchenko; 1D, R. bifue sp. nov., R. imakane sp. nov., R. misago sp. nov., and R. hamata Hattori & Ohkawa; 1E, R. shimamaki sp. nov.

FIGURE 4. Adult of Rhyacophila imakane sp. nov. 4A–4D, male: 4A, genitalia, left lateral, omitting left inferior appendage; 4B, same, dorsal; 4C, right inferior appendage, dorsal; 4D, same, ventral. 4E–4I, female: 4E, abdominal segments VIII–XI; left lateral; 4F, segment VIII, dorsal; 4G, same, ventral; 4H, vaginal apparatus, left lateral; 4I, same, ventral. Abbreviations: VIII–XI = abdominal segments VIII–XI; a inf app = apical segment of inferior appendage (paired); ae = aedeagus; an sc = anal sclerite (paired); ap ba = apical band (paired); b inf app = basal segment of inferior appendage (paired); do me pr = dorsomesal process (paired); pp = posterior process; ps = processus spermathecae; ru po IX = rugged posterior part of segment IX; sl cu pr = slender curved process (paired). Arrow, see text.