Hydroptila hahajima Ito & Sasaki, 2023

Ito, Tomiko, Sasaki, Tetsuro, Takahashi, Chicaco, Sugawara, Hirotaka & Hayashi, Fumio, 2023, The family Hydroptilidae Curtis (Trichoptera) in the Ogasawara Islands, northwestern Pacific, with particular reference to adaptive radiation in the oceanic islands, Zootaxa 5231 (2), pp. 141-164 : 157

Hydroptila hahajima Ito & Sasaki sp. nov.

( Figs 11A–11G , 12A, 12B )

Diagnosis. The male of this species resembles that of Hydroptila ishiura sp. nov. in having a narrow transverse tergal bridge of segment IX, semi-membranous lateral processes, and a subtriangular subgenital plate, but it is clearly distinguished from the latter by the forms of inferior appendages: The inferior appendages are narrowly triangular without any basoventral hooks in H. ishiura ( Figs 6B, 6D ), but the inferior appendages are subquadrate, each with a short, curled, basoventral hook in this species ( Fig. 11D )

Adult ( Figs 11A–11G ). Head, thorax, wing color, tibial spurs, processes of sternites V and VII same as for H. ishiura . Forewings each 2.0 mm in length and hind wings each 1.8 mm in male (n = 1); forewings each 2.1–2.2 mm in length and hind wings each 1.9–2.0 mm in female (n = 2). Antennae each 29-segmented, length 1.2 mm in male (n = 1); each 24–25-segmented, length 0.8–1.0 mm in female (n = 2).

Male genitalia ( Figs 11A–11E ). Segment IX (IX) annular, rather long, transverse tergal bridge narrow, together with subrectangular dorsal setose plate of segment IX (dsp IX) about 1/4 as long as segment, with deep and wide subquadrate excision at anterior margin dorsally and subtriangular excision anteroventrally. Dorsal plate (dp) semimembranous, subtriangular in dorsal view. Lateral processes (lp) semi-membranous, thick, subquadrate in lateral and ventral views. Subgenital plate (sp) thin, triangular, curved ventrad apically, slightly longer than inferior appendages (ia) in lateral and ventral views. Inferior appendages broad in basal 2/3, abruptly narrowed in apical 1/3, with pair of small, curled hooks (ch) basoventrally curved caudad and laterad apically in ventral view. Phallic apparatus (pa) long, almost straight, anterior end extending from anterior margin of segment V when retracted, without titillator.

Female genitalia ( Figs 11F, 11G ). Segment VIII relatively short, with no distinct tergite or sternite: 2–3 pairs of marginal setae on each of dorsum and venter, pair of transverse bands near ventral margin; ventral margin slightly projecting caudad at middle. Vaginal apparatus depressed, thin in lateral view, elongate-oval in ventral view.

Final instar larva and case ( Fig. 12B ). The final instar larva and case are very similar to those of H. ishiura and H. ogasawaraensis , and could not be discriminated from those of the latter two species.

Holotype. Male , Japan, Ogasawara Islands , Haha-jima: Uch ̊-zawa (N26.6526, E142.1508, 35 m above sea level), 12–13.iv.2022, TI & TS, L ( CBM-ZI 0184763 ).

Paratypes. 2 females, same data as holotype ( CBM-ZI 0184764–0184765 ) .

Other specimens. Haha-jima: 1 female, same data as holotype; 3 prepupae, 9 larvae, type locality, 1.iii.2020, TI et al., H; 1 larva, Iguma-dani, 29.ii.2020, TI et al., H ( Table 1 ) .

Distribution ( Fig. 1D ). Japan (Ogasawara Islands: Haha-jima).

Habitat ( Fig. 12A ). Larvae of this species were found in hygropetric habitat of small mountain streams.

Etymology. The species epithet refers to the name of the type locality.

Japanese name. Hahajima-hime-tobikera.

Figures

FIGURE 1. Location of the Ogasawara (Bonin) Islands in the northwestern Pacific (1A) and collecting sites of the six species of Hydroptila on Ani-jima (1B), Chichi-jima (1C), and Haha-jima (1D).

FIGURE 6. Adults of Hydroptila ishiura sp. nov. Male (6A–6E): 6A, abdominal segments I–X, left lateral; 6B, genitalia, left lateral; 6C, same, dorsal; 6D, same, ventral; 6E, phallic apparatus, left lateral. Female (6F, 6G): 6F, abdominal segments VIII–X, ventral; 6G, vaginal apparatus, ventral. Abbreviations: VIII–X = abdominal segments VIII–X; dp = dorsal plate; dsp IX = dark and setose plate of segment IX; ia = inferior appendage (paired); lp = lateral process (paired); pa = phallic apparatus; sp = subgenital plate.

FIGURE 11. Adults of Hydroptila hahajima sp. nov. and H. nagahama sp. nov. Adults of H. hahajima (11A–11G): 11A, male abdominal segments I–X, left lateral; 11B, male genitalia, left lateral; 11C, same, dorsal; 11D, same, ventral; 11E, phallic apparatus, left lateral; 11F, female abdominal segments VIII–X, ventral; 11G, vaginal apparatus, ventral.Adults of H. nagahama (11H–11N): 11H, male abdominal segments I–X, left lateral; 11I, male genitalia, left lateral; 11J, same, dorsal; 11K, same, ventral; 11L, phallic apparatus, left lateral; 11M, female abdominal segments VIII–X, ventral; 11N, vaginal apparatus, ventral. Abbreviations: VIII–X = abdominal segments VIII–X; ch = curled hook (paired); dp = dorsal plate; dsp IX = dark and setose plate of segment IX; ia = inferior appendage (paired); pa = phallic apparatus; lp = lateral process; sp = subgenital plate.

FIGURE 12. Habitats of type localities, adult and immature stages of Hydroptila hahajima sp. nov. and H. nagahama sp. nov. H. hahajima (12A, 12B): 12A, habitat; 12B, larva in case in alcohol, left lateral. H. nagahama (12C–12H): 12C, 12D, habitat; 12E, adult on light trap sheet; 12F, three pupae in crack on rock surface; 12G, larva in case in field; 12H, larva in case in alcohol. Scale bars, 1 mm.