Rhyacophila yakushima, Ito, 2021

Ito, Tomiko, 2021, The genus Rhyacophila Stephens (Trichoptera, Rhyacophilidae) in Yakushima Island, northern Ryukyu, southwestern Japan, Zootaxa 5023 (1), pp. 44-58 : 45-47

Rhyacophila yakushima sp. nov.

( Figs 2 , 6A )

Rhyacophila sp. 2 : Kuhara & Ito 2017, 16, Yakushima.

Diagnosis. This new species belongs to the R. anatina Species Group and the male resembles that of R. pacata Tsuda 1940 , found in Japan (Honshu), in having large preanal appendages and a long and thick basal segment and short sock-like apical segment of each inferior appendage ( Tsuda 1940; Ross 1956; Hattori 2005). However, the male of R. yakushima is clearly distinguished from R. pacata as follows: The preanal appendages are nearly rectangular in lateral view and the apicodorsal lobe of segment IX is present in R. yakushima ; but the appendages are long and triangular in lateral view and the lobe of segment IX is undeveloped in R. pacata . The female of this new species is also similar to that of R. pacata ( Hattori 2005) , but clearly discriminated from the latter by the presence of paired subquadrate sclerites at the base of the intersegmental membranes of VIII–X.

Adult. Lengths of forewings and hind wings: Each forewing 6.8–9.2 mm long (mean 8.1 mm, n = 21) and each hind wing 6.0– 8.3 mm (mean 7.1 mm, n = 21) in males, 8.0– 10.2 mm (mean 9.5 mm, n = 8) and 7.3–9.0 mm (mean 8.1 mm, n = 8) in females, respectively. Head dark brown, warts light brown with brown setae, antennae dark brown, scapes thicker and longer than other segments; palpi brown. Thorax dark brown dorsally. Legs brown with dark brown spurs. Wings brown with darker veins and fulvous pterostigma, whitish dots scattered on apical 2/3 of forewings in both sexes. Abdomen with dark brown tergites and light brown sternites, dark pigments scattered dorsally; scent glands of sternite V open on antero-angle mounds well encircled by sutures; small mid-ventral process on sternite VII (or VI and VII) in male and on sternite VI in female, process on sternite VI of male often very small or completely absent.

Male genitalia ( Figs 2A–2E ). In lateral view segment IX (IX) short ventrally, long dorsally, dorsal margin about 5 times as long as ventral margin, apicodorsal lobe (ad l) almost 2/3 as long as lower margin of basal segment of inferior appendage (b inf app); in dorsal view anterior margin of segment IX roundly incised, apicodorsal lobe deeply incised at apex. Preanal appendages (pre app) large, slightly longer than apicodorsal lobe, in lateral view rectangular and slightly tapered posteriorly, round apically; in dorsal view slightly narrowing apically with nearly V-shaped divergence apically. Segment X (X) little reduced, below basomesal edges of preanal appendages, slightly sclerotized, connected with anal sclerites (an sc). Anal sclerites heavily sclerotized, bowl-shaped, covered with spinules. Apical band (ap ba) small, semi-membranous, round in lateral view.

Phallic apparatus complex; phallotheca (ph) in lateral view somewhat rectangular; dorsal process (do pr) elongate, in ventral and lateral views almost parallel-sided with abruptly tapered and subacute apex; aedeagus (ae) slender, sub-truncate apically in lateral and ventral views; pair of parameres (pa) slender with numerous spindles on apical half, shorter than aedeagus.

Basal segment of each inferior appendage (b inf app) long, in lateral view with dorsal and ventral margins curved caudad and parallel to each other, anterior margin oblique, posterior margin subtruncate, in dorsal view appendages curved mesad; apical segment of each inferior appendage (a inf app) in lateral view somewhat socklike, mesal sub-marginal part with spinules.

Female genitalia ( Figs 2F–2J ). Segment VIII (VIII) large, length as long as basal width, gradually narrowing posteriorly in lateral view, parallel sided in dorsal and ventral views; posterior margin with shallow and wide incision dorsally and deep round incision ventrally. Small subquadrate sclerites at base of intersegmental membranes of segments VIII–X ventrally. Vaginal apparatus long; processus spermathecae (ps) round in ventral view, semimembranous; posterior process (pp) heavily sclerotized, long, tapered, 2.5 times as long as processus spermathecae, subacute apically.

Holotype. Male , Japan, Yakushima Island , Yakusugi-land, Ara-kawa, a tributary (30.302˚N, 130.540˚E, 1100 m a.s.l.), 12.vi.2007, TI, S ( CBM-ZI 0159996 ).

Paratypes ( SPMN-IS). Yakushima Island : 6 males, 6 females, same data as holotype ; 7 males, 1 female, type locality, 16.x.2007, TI , S; 1 male, Yakusugi-land, Ara-kawa, different tributary from the type locality, 12.vi.2007, TI , S; 1 male, Yakusugi-land, Ara-kawa, small stream, 12.vi.2007, TI , S; 2 males, 1 female, Yakusugi-land, Arakawa, Seiryu-bashi, 16.x.2007, TI , S; 1 male, Shiratani-unsuikyo, 24.iv.2003, A. Ishizuka, M; 3 males, same locality, 9.v.2006, TI , S; 1 male, Shiratani-gawa, Shiratani-bashi, 8.v.2006, TI , P; 1 female, Miyanoura, Kue-gawa, Biwatsubo-bashi, 8.v.2006, TI , L; 2 males, 1 female, Anbo-rindo, Harumaki-rokugo-bashi, 17.x.2007, TI , S; 2 males, Onoaida, Onoaida-gyoko, 24.iv.2003, A. Ishizuka.

Other specimens. Yakushima Island: 1 female, Shiratani-unsuikyo, 12.vii.1992, T. Ogata ( T. Ito) ; 1 male, Kurio, Kuromi-gawa, 2.x.1996, M. Sato (N. Kuhara); 1 male, Yoshida-gawa, Yoshida-bashi, 40 m, 25.ix.2003, N. Kuhara (N. Kuhara).

Distribution. Japan (Yakushima).

Habitat. Adults of this species were collected beside fast flowing streams with stony bottoms. They were abundant at 700 to 1200 m a.s.l., and rare at sites lower than 50 m elevation ( Fig. 6A ).

Etymology. The name “ yakushima ” is a noun in apposition, coined from the name of the island.

Japanese name. Yakushima-nagare-tobikera.

Figures

FIGURE 2. Rhyacophila yakushima sp. nov. 2A–2E, male: 2A, genitalia, left lateral; 2B, same, dorsal; 2C, same, caudal, omitting inferior appendages; 2D, phallic apparatus, ventral, with enlarged figure of apical part of a paramere; 2E, right inferior appendage, dorso-mesal.2F–2J, female: 2F, abdominal segments VIII–XI, left lateral; 2G, same, ventral; 2H, abdominal segment VIII, dorsal; 2I, vaginal apparatus, left lateral; 2J, same, ventral. Abbreviations: VIII–XI = abdominal segments VIII–XI; a inf app = apical segment of inferior appendage (paired); ad l = apicodorsal lobe; ae = aedeagus; an sc = anal sclerite (paired); ap ba = apical band; b inf app = basal segment of inferior appendage (paired); do pr = dorsal process; pa = paramere (paired); ph = phallotheca; pre app = preanal appendage; pp = posterior process; ps = processus spermathecae.

FIGURE 6. Adult collection sites of seven species of Rhyacophila on Yakushima. Solid circle = 1–4 adults collected; open circle = more than 5 adults collected.