Rhyacophila misago 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 : 561-565

Rhyacophila misago Ito & Kuhara sp. nov.

( Figs 1D , 5A–5I , 6A–6G )

Rhyacophila sp. 3 : Ito et al. 2010, pp. 56, 81, Hokkaido (Hiyama, Oshima).

Species group and diagnosis. This new species belongs to the Rhyacophila kaltatica Species Group in having the dorsal posterior margin of segment IX protruded caudad with several spiny processes, a long depressed segment X, large anal sclerite and thick inferior appendages with long basal and short apical segments. The male of this new species resembles that of R. azumaensis Kobayashi 1973 , found in Japan (northern Honshu; Fig. 1A , black stars), in having pair of slender lateral processes of the rugged posterior area of segment IX and a pair of parameres. However, the male of R. misago sp. nov. is clearly distinguishable from that of R. azumaensis as follows: The pair of long processes of the rugged posterior part of segment IX make a circle in dorsal view in R. misago and the dorsomesal process of the basal segment of each inferior appendage is arising from the subapicodorsal edge, short, and strongly curved apicodorsad; but the pair of slender processes is much shorter and gently curved caudad in dorsal view in R. azumaensis and the dorsomesal process of the basal segment of each inferior appendage is long, arising at midlength, and nearly straight.

The female of this new species is also similar to that of R. azumaensis , but can be readily discriminated from the latter as follows: In lateral view, segment VIII has a pair of small curved ridges ventroposteriorly in R. azumaensis , but is without such ridges in R. misago .

The larva of this species is similar to that of R. hamata Hattori & Ohkawa 2007 , but different from the latter by the presence of a rectangular, light color pattern on the frontoclypeal apotome of the head, whereas a rectangular pattern is absent in R. hamata .

Adult. Male: Each forewing 5.9–6.3 mm long (mean = 6.1 mm, n = 5) and each hind wing 5.4–5.8 mm (mean = 5.6 mm, n = 5). Female: Each forewing 6.6–6.9 mm (mean = 6.7 mm, n = 3) and each hind wing 5.8–6.2 mm (mean = 6.1 mm, n = 3). 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 open on anterolateral-angle mounds well encircled by sutures; small mid-ventral process on each of sternites VI and VII (or on only VII) in the male and on sternite VI in the female (process on sternite VI of male often very small or completely absent).

Male genitalia ( Figs 5A–5D ). Dorsal margin of segment IX (IX) about 3 times as long as ventral margin in lateral view. Rugged dorsal posterior part of segment IX (ru po IX) with several short acute processes near middle and pair of slender curved processes (sl cu pr) laterally; each slender process very long, directed caudad at first, curved dorsad at right angle near mid-length in lateral view and configured as semicircle in dorsal view. Segment X (X) depressed; subtriangular with incised apical margin in dorsal view; slender bar-like with slightly thickened apices in lateral view. Anal sclerite (an sc) strongly sclerotized, wide basally, gradually narrowing posteriorly with short longitudinal slit on midline apically in dorsal view; subrectangular with large, tall, subquadrate process basally in lateral view. Tergal strap (te st) and apical band (ap ba) membranous, vertically high in lateral view. Aedeagus (ae) long and slender. Each paramere (par) semicircular in ventral view, slender basally, gradually thickened to mid-length, and round apically in lateral view.

Basal segment of each inferior appendage (b inf app) long, 2.5 times as long as apical segment (a inf app), in lateral view with dorsal and ventral margins parallel with each other; dorsomesal process (do me pr) arising from mesal side near dorso-caudal corner of basal segment, heavily sclerotized, hook-like in dorsal view, about 1/4 as long as basal segment; apical segment of each inferior appendage (a inf app) oval, diagonally positioned in lateral view, oblong in dorsal and ventral views, mesal surface dorsally and apically with numerous spinules.

Female genitalia ( Figs 5E–5I ). Segment VIII (VIII) short, 0.8 times as long as basal height, gradually narrowing posteriorly in lateral, dorsal, and ventral views; posterolateral margins gently convex in lateral view, widely incised as V-shaped in dorsal view, shallowly and widely incised in ventral view. Vaginal apparatus long; processus spermathecae (ps) round in ventral view, semi-membranous; posterior process (pp) sclerotized, long, 1.5 times as long as processus spermathecae, round apically.

Final Instar Larva. ( Fig. 6 ). Length up to 15 mm, width up to 2.5 mm, relatively stumpy.

Head ( Figs 6A–6C ). Width 0.86–0.96 mm (mean = 0.90 mm, n = 4); width: length: depth about 1.0: 1.6: 1.5. Brown with dark brown dots on parietals; frontoclypeal apotome dark brown with light colored rectangular pattern at middle separating darker regions laterally and anteriorly and with transverse pattern of four muscle scars at posterior part. Eyes rectangular. Labrum light brown, subquadrate with slightly incised anterior margin and 5 pairs of setae. Mandibles robust, deep brown, asymmetrical; left one with acute apex and mesal blade; right one with acute apex and mesal hump.

Thoracic segments ( Figs 6A, 6D–6F ). Pronotum completely covered with 2 light brown plates, anterolateral corners round, slightly narrowing posteriorly, incised mesally and rugged and darker in color along posterior margin; 13–15 setae on setal areas 1–3 (sensu Wiggins 1996), many slender short setae on anterior edge. Meso- and metanota membranous; dark brown with several light color markings dorsally, almost white ventrally.

Foretrochantin of prothorax and pleura of meso- and metathoraxes well developed. Forelegs short and somewhat stout, middle and hind legs rather slender.

Abdomen ( Figs 6A, 6G ). Moderately depressed dorsoventrally, gills absent. Segments I–VIII dark brown with several light color markings and 1–3 setae dorsally; near white ventrally. Dorsal ellipsoidal sclerite on segment IX. Anal legs each with freely projecting lateral basoventral hook; apical claw with two ventral teeth, basal tooth smaller than distal tooth.

Holotype. Male, Hokkaido, Oshima, Fukushima-chô , Misago-no-taki (42.5022°N, 140.3269°E, 5 m a.s.l.), 4.viii.2006, leg. TI & TH, S ( CBM-ZI 0189176 ).

Paratypes. 1 male, 2 females, same data as holotype ( SPMN-IS) ; 1 male, type locality, 4.viii.2007 (pupa), reared and emerged on 29.viii.2007, leg. TI ( SPMN-IS) ; 2 males, type locality, 30.ix.2007, leg. TI , S ( SPMN-IS).

Other specimens. Hokkaido, Oshima: Yakumo-chô , Goyô-no-sawa, 6 males, 22.vii.1997, leg. TI & AO, S ( SPMN-IS). Yakumo-chô, small waterfall beside Yûrappu-gawa , 1 male, 1 female, 4 larvae, 23.vii.1997, leg. TI & AO, S ( SPMN-IS). Yakumo-chô, small waterfall beside Yûrappu-gawa , 1 male, 1 female, 23.vi.1995, leg. TI , S ( TI). Yakumo-chô, small water flow beside Namari-gawa , 1 male, 1 female, 22.vi.2003, leg. HM , S ( HM). Mori-machi, Himekawa, small waterfall beside Ojironai-gawa , 2 males, 10.vi.1980, leg. TI , S ( SPMN-IS). Mori-machi, waterfall beside Torisaki-gawa , 1 male, 24.vi.2003, leg. NK , S ( NK). Mori-machi, Torisaki Keikoku , 1 pupa (male), 5.viii.2007, leg. TI & TH ( SPMN-IS). Fukushima-chô , Misago-no-taki (type locality), 1 male, 1 female, 20.vi.2023, leg. TI , S ( TI). Fukushima-chô , Shiraito-no-taki, 1 larva, 30.ix.2007, leg. TI ( SPMN-IS) . Fukushima-chô, Fudôno-taki , 1 male, 1 female, 12.ix.2006, leg. TI , S ( SPMN-IS). Fukushima-chô, Iwabe-gawa , near estuary, 1 male, 21.vi.1995, leg. NK , S ( NK).

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

Habitat. Adults of this species were collected beside waterfalls and small, fast flowing streams.

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

Japanese name. Misago-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 5. Adult of Rhyacophila misago sp. nov. 5A–5D, male: 5A, genitalia, left lateral, omitting left inferior appendage; 5B, same, dorsal; 5C, right inferior appendage, dorsal; 5D, right inferior appendage and phallic apparatus, ventral. 5E–5I, female: 5E, abdominal segments VIII–XI, left lateral; 5F, segment VIII, dorsal; 5G, same, ventral; 5H, vaginal apparatus, left lateral; 5I, 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); par = paramere (paired); pp = posterior process; ps = processus spermathecae; ru po IX = rugged posterior part of segment IX; sl cu pr = slender curved process (paired); te st = tergal strap (paired).

FIGURE 6. Larva of Rhyacophila misago sp. nov. 6A, habitus, left lateral; 6B, head, dorsal; 6C, mandibles, ventral; 6D, pronotum, dorsal; 6E, pleuron and right foreleg, right lateral; 6F, pleuron and right hind leg, right lateral; 6G, left anal proleg, left lateral.