Rhyacophila nagata, Ito, 2021

Ito, Tomiko, 2021, The genus Rhyacophila Stephens (Trichoptera, Rhyacophilidae) in Yakushima Island, northern Ryukyu, southwestern Japan, Zootaxa 5023 (1), pp. 44-58 : 51-53

Rhyacophila nagata sp. nov.

( Figs 5 , 6D )

Diagnosis. This new species belongs to the R. ulmeri Species Group (see Discussion), and the male resembles that of R. kuramana Tsuda 1942 , found in Japan (Honshu, Shikoku, Kyushu), in having a large bowl-like apicodorsal lobe of segment IX and round preanal appendages in lateral view. Although geographic variations of R. kuramana are found in the shape of the apical segments of the inferior appendages of males by Hattori (2005), the two species are clearly discriminated in that three small granulate protuberances are present near the ventrocaudal edge of the apicodorsal lobe of segment IX in R. nagata , but are absent in R. kuramana ( Hattori 2005) . The female of R. nagata is characterized by a long segment VIII, similar to that of R. kuramana , but can be distinguished from the latter by presence of a distinct incision at the posteroventral margin of segment VIII and the absence of this incision in R. kuramana .

Adult. Lengths of forewings and hind wings: Each forewing 5.0–7.0 mm long (mean 6.2 mm, n = 18) and each hind wing 4.2–6.1 mm (mean 5.4 mm, n = 18) in males, 5.9–7.2 mm (mean 6.8 mm, n = 8) and 5.2–6.9 mm (mean 5.8 mm, n = 8) in females, respectively. Head dark brown, warts light brown with brown setae, antennae 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, a few whitish dots on forewings of both sexes. Abdomen with brown tergites and light brown sternites, dark pigments scattered dorsally; 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 5A–5F ). Segment IX (IX) in lateral view with dorsal margin 1.5 times as long as ventral margin; apicodorsal lobe (ad l) large, bowl-like, in dorsal view with granulate mesal lobe bearing three small protuberances (sm pr) near antero-ventral edge. Preanal appendages (pre app) in lateral view round, plate-like with stems short; broad in dorsal view, middle part semi-membranous. Segment X (X) weakly sclerotized, near bases of preanal appendages, roundish in caudal view, invisible in lateral view. Anal sclerites lacking. Apical band (ap ba) small, roundish in lateral and caudal views. Tergal band (t b) connected apically with apical band and basally with phallotheca.

Phallotheca (ph) large, endotheca (end) membranous. Aedeagus (ae) gradually narrowing and curved dorsad in lateral view, in ventral view broader in middle, round apically with deep middle incision nearly surrounding very slender apicomesal bar. Parameres (pa) slender, twice as long as aedeagus, elongate caudally, slightly curved dorsomesad in lateral and ventral views, gradually tapered and acute apically.

Inferior appendages large, each with basal segment (b inf app) almost parallel-sided and caudal margins slightly convex in lateral view; apical segment (a inf app) short, about 1/3 times as long as basal segment, ventral 2/5 protruding posterad, dorsal 3/5 not protruding, spinous posteriorly.

Female genitalia ( Figs 5G–5K ). Segment VIII (VIII) long, length twice basal width, gradually narrowing posteriorly in lateral view, with distinctly incised posterior margins in dorsal and ventral views. Weakly sclerotized intersegmental membrane invaginated within apex of VIII, 2/5 length of VIII. Vaginal apparatus long, processus spermathecae (ps) membranous, posterior process (pp) heavily sclerotized, slightly undulate basally, subacute apically.

Holotype. Male , Japan, Yakushima Island , Nagata, Nagata-gawa, small tributary (30.384˚N, 130.436˚E, 95 m a.s.l.), 10.v.2006, TI, S ( CBM-ZI 0159999 ).

Paratypes ( SPMN-IS). Yakushima Island : 6 males, 1 female, same data as holotype ; 1 male, Yakusugiland, Ara-kawa, Seiryu-bashi, 16.x.2007, TI , S; 1 female, Arakawa, tributary, 16.x.2007, TI , S; 2 females, Anbo, Harumaki-rokugo-bashi, 17.x.2007, TI , S; 5 males, 1 female, Anbo, Harumaki-yongo-bashi, 16–17.x.2007, TI , P; 3 males, 1 female, Isso, Nunobiki-no-taki, 17.x.2007, TI , S; 2 males, Miyanoura-gawa, tributary, 10.v.2006, TI , S; 1 female, Shiratani-unsuikyo, 9.v.2006, TI , S.

Other specimens. Yakushima Island: 1 female, Ara-kawa, 1200 m, 25–28.vi.2007, T. Yamauchi et al., M ( T. Ito) : 1 male, near Shin-tomizuka-goya, small stream, 26.ix.2003, N. Kuhara (N. Kuhara).

Distribution. Japan (Yakushima).

Habitat. Adults of this species were collected beside streams with stony bottoms located at 25 to 1400 m a.s.l. ( Fig. 6D ).

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

Japanese name. Nagata-nagare-tobikera.

Figures

FIGURE 5. Rhyacophila nagata sp. nov. 5A–5F, male: 5A, genitalia, left lateral; 5B, same, caudal; 5C, same, left lateral, inferior appendages omitted and apicodorsal lobe of segment IX protracted; 5D, apicodorsal lobe of segment IX and preanal appendages, dorsal; 5E, phallic apparatus, left lateral; 5F, same, ventral, with enlargement of apices of parameres and aedeagus. 5G–5K, female: 5G, abdominal segments VIII–XI, left lateral, intersegmental sclerite retracted; 5H, same, ventral; 5I, segment VIII, ventral, intersegmental sclerite protracted; 5J, same, dorsal, intersegmental sclerite retracted; 5K, vaginal apparatus, ventral; 5L, same, left lateral. Abbreviations: VIII–XI = abdominal segments VIII–XI; a inf app = apical segment of inferior appendage (paired); ad l = apicodorsal lobe of segment IX; ae = aedeagus; ap ba = apical band; b inf app = basal segment of inferior appendage (paired); end = endotheca; in sc = intersegmental sclerite (protracted in Fig. 5I); pa = paramere (paired); ph = phallotheca; pre app = preanal appendage (paired); pp = posterior process; ps = processus spermathecae; sm pr = small protuberance (one of three); t b = tergal band.

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.