Rhyacophila eniwa 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 : 552-556

Rhyacophila eniwa Ito & Kuhara sp. nov.

( Figs 1B, 1C , 2A–2I )

Rhyacophila sp. 5 : Ito et al. 2010, pp. 56, 81, Hokkaido (Shiribeshi, Hiyama, Oshima).

Rhyacophila sp. 4 : Kuhara 2011, pp. 52, 62, Hokkaido (Ishikari).

Species group and diagnosis. This new species belongs to the Rhyacophila sibirica Species Group, in having a depressed dorsal branch of segment X, erectile ventral lobe of aedeagus, and thick inferior appendages. The male of R. eniwa resembles those of R. narvae Navás 1926 found in Russia (Siberia, Khabarovsk, Primorye), North Korea, and Alaska ( Fig. 1A , crosses); R. tonneri Mey 1989 found in North Korea (Hyesan) ( Fig. 1A , double circle); and R. arefini Lukyanchenko 1993 found in Far East Asia (Hokkaido, South Kuril, Sakhalin) ( Figs 1A–1C , black circles) ( Mey 1989; Lukyanchenko 1993; Arefina 1997; Vshivkova & Khalin 1997; Hattori 2005; Ivanov 2011). However, the male of this new species is clearly distinguished from those of the three known species by the shapes of the dorsal and ventral braches of segment X as follows: The lateral view of the ventral branch of segment X is semicircular in R. eniwa , but subquadrate in the three known species. Moreover, two common species in Hokkaido ( Figs 1B, 1C ), R. eniwa and R. arefini , are discriminated from each other by the lateral view of the dorsal branch of segment X; i.e., the branch gently curved dorso-caudad at mid length in R. eniwa , but not curved and almost straight in R. arefini .

The female of this new species is also similar to those of R. narvae , R. tonneri , and R. arefini , in having a relatively short segment VIII ( Mey 1989; Lukyanchenko 1993; Arefina 2001; Hattori 2005); but is clearly discriminated from the latter by the shape of abdominal segment VIII as follows: The segment gradually narrows posteriorly in lateral, dorsal, and ventral views, and the posterior margin is clearly incised in dorsal and ventral views in R. eniwa ; but the posterior margins are almost straight or very shallowly incised in R. narvae and R. arefini ; and very slightly narrowing posteriorly in lateral view and with the posterior margin slightly incised in dorsal view in R. tonneri .

Adult. Male: Each forewing 6.0–7.0 mm long (mean = 6.7 mm, n = 5) and each hind wing 5.2–6.0 mm (mean = 5.6 mm, n = 5). Female: Each forewing 7.3–8.8 mm (mean = 7.9 mm, n = 5) and each hind wing 6.0– 7.7 mm (mean = 6.7 mm, n = 5). Head dark brown, warts light brown with brown setae, antennae dark brown, palpi brown. Thorax dark brown dorsally. Legs light brown or 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 2A–2D ). Dorsal margin of segment IX (IX) about 1.7 times as long as ventral margin in lateral view. Dorsal branch of segment X (do br X) almost 1.7 times as long as dorsal margin of segment IX and gently curved dorsocaudad at mid length in lateral view; in dorsal view, short subrectangular, length 1.1–1.3 times maximal width ( Fig. 2C ), caudal margin widely concave with two low apices around middle. Ventral branch of segment X (ve br X) semicircular in lateral view. Apical band (ap ba) sclerotized, shallowly bowl-like in lateral view, round and covered with spinules apically in caudal view.

Phallic apparatus complex. Dorsal process (do pr) heavily sclerotized, elongate, round apically in lateral view, subquadrate in caudal view, covered with short spinules apically. Ventral process (ve pr) heavily sclerotized, elongate, roundish apically in lateral view, almost square apically in caudal view. Parameres (par) slender, directed ventrocaudad, very spiny apically. Aedeagus (ae) directed ventrocaudad at basal 3/4, curved dorsocaudad at apical 1/4, truncate apically. Ventral lobe of aedeagus (ve lo) erectile, spoon-shaped with numerous spindles distally.

Inferior appendages thick, robust; basal segment (b inf app) long and thick in lateral view with dorsal and ventral margins parallel to each other and directed dorsocaudad; apical segment (a inf app) short, 0.7 times as long as basal segment, sock-shaped in lateral view, with numerous spinules mesally at apical half.

Female genitalia ( Figs 2E–2I ). Segment VIII (VIII): length almost as long as basal height, gradually narrowing posteriorly in lateral view, slightly broader near base and gradually narrowing posteriorly in dorsal and ventral views; dorso-posterolateral margin slightly convex in lateral view, distinctly incised in dorsal and ventral views. Vaginal apparatus long; processus spermathecae (ps) semi-membranous, round with bilobed apex in ventral view, bowl-like in lateral view; posterior process (pp) long, heavily sclerotized, swollen around middle, round apically.

Larva. Unknown.

Holotype. Male, Hokkaido, Ishikari, Eniwa-shi , Ichankoppe-zawa (42.8224°N, 141.3797°E, 310 m a.s.l.), 25.vi.2003, leg. TI, S ( CBM-ZI 0189173 ).

Paratypes. 6 males, 8 females, same data as holotype ( SPMN-IS) ; 2 males, type locality, 31.vii.1994, leg. TI , M ( SPMN-IS).

Other specimens. Hokkaido, Ishikari: Eniwa-shi, Ichankoppe-zawa , 240 m, small tributary, 1 male, 20– 30.vi.1995, leg. TI , M ( TI); 1 male, 26.vi.2011, leg. TI , S ( TI); 2 males, 10.vii.2007, leg. TI , S ( TI); 1 male, 26.vi.2011, leg. TI , S ( TI). Chitose-shi, Shikotsu-kohan, Poropinai , small stream, 1 female, 11.vii.1997, leg. TI , M ( NK). Chitose-shi, Bifue , small stream beside old road, 2 males, 14.vii.2009, leg. NK , M ( NK). Chitose-shi, Bifue-gawa , small tributary, 4 males, 21.vi.2003, leg. HM , S ( HM); 19 males, 5 females, 21.vi.2003, leg. TI , S ( TI). Chitose-shi, Bifue, near Kusabue-rindo , spring, 10 males, 4 females, 21.vi.2012, leg. NK , M ( NK); 40 males, 18 females, 8.vii.2012, leg. NK , M ( NK); 12 males, 13 females, 21.vii.2012, leg. NK , M ( NK); 3 males, 7 females, 3.viii.2012, leg. NK , M ( NK); 3 females, 17.viii.2012, leg. NK , M ( NK); 1 male, 3 females, 1.ix.2012, leg. NK , M ( NK). Chitose-shi, Fujino-sawa, Mamachi-gawa , tributary, 100 m, 2 males, 27.vi.2014, leg. NK , M ( NK). Shiribeshi: Kyôgoku-chô, Kawanishi , Fukidashi-kôen , 3 males, 1 female, 11.v.1988, leg. TI , S ( TI); 12 males, 1 female, 30.vi.1998, leg. TI & AO, S ( SPMN-IS); 3 males, 5.viii.2007, leg. TI & AO, S ( TI); 21 males, 3 females, 11.vi.2011, leg. NK , S ( NK). Rankoshi-chô, Mikasa , salmon hatchery, 8 males, 19.vi.1982, leg. TI , S ( TI). Shimamaki-mura , Nagumo-no-sawa, upper reach, 1 male, 5.vi.2006, leg. TI , S ( TI); 5 males, 8 females, 5.viii.2008, leg. TI , S ( SPMN-IS); 2 males, 10.vi.2009, leg. TI , S ( SPMN-IS). Iburi: Tomakomai-shi, Takaoka , Horonai-gawa , source, 2 males, 4 females, 21.vi.1981, leg. TI , S ( TI). Tomakomai-shi, Maruyama, Yûfutsu-gawa , source, 39 males, 22 females, 10.vi.2009, leg. NK , M ( NK); 45 males, 45 females, 24.vi.2009, leg. NK , M ( NK); 57 males, 38 females, 10.vii.2009, leg. NK , M ( NK); 8 males, 6 females, 10.viii.2009, leg. NK , M ( NK); 1 male, 3 females, 28.viii.2009, leg. NK , M ( NK); 1 male, 16.ix.2009, NK , M ( NK); 2 males, 29.v.2010, leg. NK , M ( NK); 8 males, 5.vi.2010, leg. NK , M ( NK). Date-shi, Ôtaki-ku , Aichi, spring beside Shiribetsu-gawa , 430 m, 2 males, 1 female, 25.vi.2011, leg. NK , M ( NK). Date-shi, Ôtaki-ku , Aichi, Shiribetsu-gawa , source, 590 m, 3 males, 1 female, 25.vi.2011, leg. NK , M ( NK); 9 males, 7 females, 14.vii.2011, leg. NK , M ( NK). Sôbetsu-chô, Orofure-tôge , 810 m, 3 males, 25.vi.2011, leg. NK , M ( NK); 13 males, 7 females, 14.vii.2011, leg. NK , M ( NK); 3 males, 4 females, 31.vii.2011, leg. NK , M ( NK). Sôbetsu-chô, Benkei , small stream, 1 male, 1 female, 25.vi.2011, NK , M ( NK); 1 male, 14.vii.2011, leg. NK , M ( NK). Oshima: Hokuto-shi, Nakayama , Kuro-taki , 3 pupae (1 male, 2 females), 4.viii.2006 (prepupae), reared and put into alcohol on 4.ix.2006, leg. TI & TH ( SPMN-IS). Matsumae-chô, Kokamotsu-gawa , 490 m, 5 males, 13 females, 3.vii.2005, leg. NK , S ( NK).

Distribution ( Figs 1B, 1C , white squares). Hokkaido (central and southwestern areas).

Habitat. The adults of this species were collected in mountain areas near springs, waterfalls, and small streams up to several meters wide.

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

Japanese name. Eniwa-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 2. Adult of Rhyacophila eniwa sp. nov. 2A–2D, male: 2A, genitalia, left lateral, omitting left inferior appendage; 2B, same, caudal, omitting inferior appendages; 2C, dorsal branch of segment X, dorsal; 2D, right inferior appendage, ventral. 2E–2I, female: 2E, abdominal segments VIII–XI, left lateral; 2F, segment VIII, dorsal; 2G, same, ventral; 2H, vaginal apparatus, left lateral; 2I, same, ventral. Abbreviations: VIII–XI = abdominal segments VIII–XI. a inf app = apical segment of inferior appendage (paired); ae = aedeagus; ap ba = apical band (paired); b inf app = basal segment of inferior appendage (paired); do br X = dorsal branch of segment X; do pr = dorsal process of phallobase; par = paramere; pp = posterior process; ps = processus spermathecae; ve br X = ventral branch of segment X; ve lo = ventral lobe of aedeagus; ve pr = ventral process of phallobase (paired).