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Hydroptila nagahama Ito & Sasaki sp. nov. (Figs 11H–11N, 12C–12H) Diagnosis. The male of this species resembles that of Hydroptila ishiura sp. nov. in having a narrow transverse tergal bridge of segment IX and an almost straight phallic apparatus, but it is clearly distinguished from the latter by the forms of inferior appendages and absence of a subgenital plate or lateral processes: The inferior appendages are narrowly triangular in H. ishiura (Figs 6B, 6D), but the inferior appendages are each subquadrate with a strongly sclerotized, large claw and three stout spines on its caudodorsal margin in this species (Figs 11I, 11K). Adult (Figs 11H–11N, 12E). 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 = 2); forewings each 2.0 mm in length and hind wings each 1.8–1.9 mm in female (n = 2). Antennae each 28-segmented, length 1.1 mm in male (n = 2); each 25-segmented, length 0.9–1.0 mm in female (n = 2). Male genitalia (Figs 11H–11L). Segment IX (IX) annular, rather long, about 2.2 times longer than height, transverse tergal bridge narrow, on midline about 1/6 as long as segment, with transverse dark and setose plate (dsp IX) not projecting and with deep and wide circular excisions at anterior margins dorsally and ventrally. Dorsal plate (dp) semi-membranous, trapezoidal with mesal concavity at caudal margin in dorsal view; thick and triangular with subacute apex, longer than inferior appendages and curved ventrad in lateral view. Inferior appendages (ia) subquadrate with strongly sclerotized, large claw ventromesally, thick spine caudoventrally, and three thick spines caudodorsally. Phallic apparatus long, almost straight, anterior end extending from middle of segment VI when retracted, without titillator. Lateral processes and subgenital plate absent. Female genitalia (Figs 11M, 11N). 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 (Figs 12G, 12H). The final instar larva and case of this species are very similar to those of H. ishiura, H. ogasawaraensis, and H. hahajima, and could not be discriminated from those of the latter three species. Holotype. Male, Japan, Ogasawara Islands, Haha-jima: Nagahama (N26.6736, E142.1502, 130 m above sea level), 12.iv.2022, TI & TS, L (CBM-ZI 0184766). Paratypes. 1 male, 2 females, same data as holotype (CBM-ZI 0184767–0184769). Other specimens. Haha-jima: 8 females, 4 pupae (1 male, 3 females), 81 larvae, type locality, 28.ii.2020, TI et al., L & H; 1 male, type locality, 21.xii.2021, TS & Y. Kaga, L; 1 larva, Iguma-dani, 29.ii.2020, TI et al., H (Table 1). Distribution (Fig. 1D). Japan (Ogasawara Islands: Haha-jima). Habitat (Figs 12C, 12D, 12F). Larvae and pupae were found on surfaces of hard rocks and in small concavities of hygropetric habitat in small mountain streams, respectively. Etymology. The species epithet refers to the name of the type locality. Japanese name. Nagahama-hime-tobikera.

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.

Hydroptila demersa Ito & Sasaki sp. nov. (Figs 3–5) Diagnosis. The male of this species resembles to that of H. ogasawaraensis described from Chichi-jima, Ogasawara Islands, in having a narrow transverse tergal bridge of segment IX, a subtriangular subgenital plate, and an almoststraight phallic apparatus with short titillator, but it is clearly distinguished from the latter by the form of the inferior appendages: Inferior appendages are without any processes in H. ogasawaraensis (Figs 9B, 9D), but each has a dorsolateral hump in this species (Figs 3E, 3G). The larva of this species is distinct from those of other congeneric species by the rather oblong and depressed form of the head capsule. Adult male (Fig. 3). Head: Postoccipital warts large, ellipsoidal, ocelli absent. Maxillary palps each 5- segmented, labial palps each 3-segemented. Mesoscutellum flabellate and without transverse suture. Metascutellum wide, subtriangular. Wings black to dark brown, some light brown patterning in forewings, but often indistinct in alcohol specimens; light brown dots absent in hind wings; forewings each 1.9–2.1 mm in length and hind wings each 1.7–1.9 mm (n = 5). Antennae each 27–29-segmented, length 1.0– 1.1 mm (n = 5); brown with three white bands at antero-middle, postero-middle and apices. Tibial spur formula 0, 2, 4. Pair of anterolateral processes of sternite V each with 2 apical setae, one long and one short. Short, subacute, posteroventral process on sternite VII. Male genitalia (Figs 3D–3H). Segment IX (IX) annular, dorsally with deep and wide circular excision at anterior margin and with shallow and wide excision at posterior margin, resulting transverse tergal bridge narrow, 1/4 as long on midline as segment in dorsal view; no dark and setose plate evident. Dorsal plate (dp) subquadrate in dorsal view with small posteromesal concavity, semi-membranous. Subgenital plate (sp) slightly sclerotized, gradually tapered, directed caudoventrad basally, then curved caudad at apical 1/4 with acute apex in lateral view, blunt in ventral view. Inferior appendages (ia) thick; directed caudoventrad at basal 2/3 and caudodorsad at apical 1/3; each with dorsolateral hump (dh) at middle, acute apically, covered with fine setae and spines. Phallic apparatus (pa) long, almost straight, extending from anterior 1/3 of segment VI when retracted, with short titillator at mid-length. Female. Unknown. Immature stages. Final instar larva (Fig. 4). Body somewhat compressed laterally, length up to 2.5 mm, sclerotized parts light brown, membranes milky white. Head (Figs 4A–4D). Depressed dorsoventrally, subrectangular with almost parallel sides in dorsal view, width up to 0.55 mm; width: length: height = about 1.00: 1.85: 0.70. Dorsal ecdysial lines indistinct, longest setae (setae no. 9, sensu Wiggins 1996) about twice as long as width of head, seta no. 8 (sensu Wiggins 1996) also long, about 1.5 times as long as width of head. Antennae situated near anterolateral corners of head capsule, each unsegmented with short sensilla apically and seta subapically. Small spines (sensu Wells 1985, 1997) absent on dorsum. Thorax (Figs 4A, 4B, 4E). Dorsum of each segment covered with pair of large square sclerotized plates; these plates light brown, with slightly darkened posterior margins; each plate with about 20 setae on pronotum, about 15 setae on each plate of meso- and metanota. Thoracic legs essentially similar in structure and subequal in three legs; foretibiae each with spur having two spines, spines with few fine teeth, spatulate spines indistinct. Foretrochantins and pleura of meso- and metathoraces subrectangular, pleural sutures indistinct. Abdomen (Figs 4A, 4F, 4G). Somewhat compressed laterally, slightly taller at segments III–VI. Tracheal gills, humps, lateral fringes, and lateral tubercles absent. Small, transversely oval chloride epithelia dorsally present on segments I–VI. Paired long sa 1 setae, two short sa 2 setae, and single long sa 3 seta directed laterad on each of segments I –VIII. Tergite IX transversely ellipsoidal with two pairs of long setae and two pairs of short setae. Lateral sclerites of segment X round with one pair of long and two pairs of short setae. Anal claws directed anterolaterad, each with two short and wide accessory hooks. Three anal gills slender, one on middle of dorsum of segment IX behind tergite, pair on posterolateral margins of segment X. Case (Figs 5A, 5B). Case of final instar larva up to 2.9 mm, composed of elongate-ellipsoidal right and left valves, very slightly compressed laterally, made of mineral particles with rather rough surface, never of organic materials. Holotype. Male, Japan, Ogasawara Islands, Chichi-jima: Ishiura-kita River, upper reach (N27.0756, E142.2221, 230 m above sea level), 26.ii.2020, TI, TS & CT (TI et al.), S (CBM-ZI 0184755). Paratypes. 2 males, same data as holotype (CBM-ZI 0184756–0184757). Other specimens. Chichi-jima: 2 males, 2 pupae, 2 larvae, same data as holotype; 1 male, 4 pupae, 4 larvae, type locality, 12–13.iv.2019, TI et al., S & H; 1 larva, Hatsuneura-gawa, 7.iv.2009, G. Yoshinari; 1 pupa, 1 prepupa, same locality, 15.iv.2019, TI et al., H; 2 males, 2 pupae, Fukiage-dani, 14.iv.2019, TI & TS, S & H; 3 males, 1 pupa, 2 larvae, same locality, 2.iii.2020, TI & CT, S & H. Ani-jima: 10 males, Takinoura-gawa, 3.iii.2020, TI et al., S. Remarks and habitat (Figs 5C, 5D). The larva of this species is very distinct in having a rather depressed, oblong head with rather long setae (no. 8) ventrally. As far as we know, such a head has not been known in any congeneric species in North America (Ross 1944; Wiggins 1996), Australia (Wells 1985, 1997), Europe (Wallace et al. 2003; Waringer & Graf 2011), Angola (Wells & de Moor 2020), or Japan (Ito 2021). In caddisflies, the depressed form of the larval head is known for four rhyacophilid species that burrow into sandy stream beds (Taira & Tanida 2011, 2013) and in a philopotamid species inhabiting the hyporheic zone (Torii et al. 2022). Therefore, depressed larval heads, and probably also long setae on the ventral side of the head capsule of H. demersa might be an adaptive form for their microhabitat, the underside or interstices of stony or sandy substrates in shallow water flowing in narrow, steep, mountain streams, up to 5 cm depth and 100 cm width. Absence of small spines on the dorsum of the head is also exceptional, since they are numerous and scattered in many species of Hydroptila larvae (Wells 1985; Ito 2021). The cases of this species, very slightly compressed with rough surfaces, are different from those of other congeneric species (Ross 1944; Wells 1985; Wiggins 1996; Wallace et al. 2003; Waringer & Graf 2011; Ito 2021). This species was sometimes collected with H. ishiura sp. nov. in the same streams, but in fewer numbers than the latter. Distribution (Figs 1B, 1C). Japan (Ogasawara Islands: Chichi-jima, Ani-jima). Etymology. The species epithet (a Latin adjective) refers to the depressed form of the larval head. Japanese name. Muguri-hime-tobikera.

Hydroptila ishiura Ito & Sasaki sp. nov. (Figs 6–8) Diagnosis. The male of this species resembles to that of Hydroptila demersa in having a narrowly transverse tergal bridge of segment IX, a subtriangular subgenital plate, and an almost-straight phallic apparatus with a short titillator, but it is clearly distinguished from the latter by presence of lateral processes and the form of the inferior appendages; a pair of lateral processes is absent and inferior appendages are curved dorsad apically in H. demersa (Figs 3E, 3G), but lateral processes are present and inferior appendages are curved ventrad apically in this species (Figs 6B, 6C). Also, the male has a dark and setose plate that is subtriangular on the apicodorsal margin of segment IX; this plate is absent in H. demersa. Adult (Figs 6, 8A). Head, thorax, wing color, tibial spurs, processes of sternites V and VII as for H. demersa. Forewings each 2.0– 2.1 mm in length and hind wings each 1.8–2.0 mm in male (n = 5); forewings each 2.1–2.2 mm in length and hind wings each 1.8–1.9 mm in female (n = 3). Antennae each 27–29-segmented, length1.0– 1.2 mm in male (n = 5); each 24–27-segmented, length 0.9–1.0 mm in female (n = 3). Male genitalia (Figs 6A–6E). Segment IX (IX) annular, transverse tergal bridge narrow, its dorsal midline 1/5 as long as segment; with deep and wide circular excision at anterior margin ventrally and dorsally, especially deep dorsally; dark and setose plate (dsp IX) well-sclerotized, subtriangular, covered with very fine setae at posterodorsal margin. Dorsal plate (dp) semi-membranous, blunt or round apically in dorsal and lateral views. Pair of lateral processes (lp) weakly sclerotized, wrapping around dorsal plate in dorsal view. Subgenital plate (sp) slightly sclerotized, gradually tapered, directed caudad, with small ventral hump at apical 1/3, subacute apically in lateral view. Inferior appendages (ia) thick; directed caudad at basal 2/3 and caudoventrad at apical 1/3, acute apically. Phallic apparatus long, almost straight, anterior end extending from almost anterior margin of segment VII when retracted, with short titillator near 3/5 length. Female genitalia (Figs 6F, 6G). Segment VIII relatively short, with no distinct tergite or sternite: 2 or 3 pairs of marginal setae on each of dorsum and venter, pair of fine transverse bands near bases of ventral marginal setae; ventral margin distinctly projected caudad at middle in ventral view. Vaginal apparatus depressed, oval in ventral view. Immature stages. Final instar larva (Fig. 7). Body somewhat depressed dorsoventrally, length up to 2.5 mm, sclerotized parts black to dark brown, membranes milky white. Head (Figs 7A–7D). Oval in dorsal view, width up to 0.44 mm; width: length: height = about 1.00: 1.20: 0.80. Dorsal ecdysial lines indistinct, longest seta (seta no. 9, sensu Wiggins 1996) about 1.1 times as long as width of head, seta no. 8 (sensu Wiggins 1996) about 0.5 times as long as width of head. Antennae situated near anterolateral corners of head capsule, each unsegmented with short round sensilla apically and long seta subapically. Small spines (sensu Wells 1985) absent on dorsum. Thorax (Figs 7A, 7B, 7E). Dorsum of each segment covered with pair of large, square, dark brown sclerotized plates; each plate with 25–30 setae on pronotum, about 15 setae on each of meso- and metanota. Thoracic legs essentially similar in structure and subequal in three legs; foretibiae each with spur having two spines, spines with few fine teeth, spatulate spines small. Foretrochantins and pleura of meso- and metathoraces rectangular, pleural sutures indistinct. Abdomen (Figs 7A, 7B, 7F, 7G). Somewhat depressed dorsoventrally, slightly broader at segments III–VI. Tracheal gills, humps, lateral fringes, and lateral tubercles absent. Segment I with two short, transversely wide dorsal sclerites arranged in succession (presumably associated with chloride epithelium or setal areas sa 1 and sa2, Wiggins 1996), with one pair and two pairs of setae, respectively, and pair of small basal sclerites at setal area sa 3 (sensu Wiggins 1996), each with two setae. Segments II–VI with transverse-oval chloride epithelia and pair of setae at sa 1. On segments II–IV, basal sclerites of sa 2 larger than those of posterior segments. Tergite IX ellipsoidal with one pair of long and two pairs of short setae. Lateral sclerites of segment X round, each with one pair of long and one pair of short setae. Anal claws directed anterolaterad, each with two accessory hooks dorsally. Three anal gills slender, one on middle of dorsum of segment IX behind tergite, pair on posterolateral margins of segment X. Variation (Figs 7B, 7F). Dorsal sclerites of abdominal segment I variable individually, anterior sclerite sometimes with middle excision, separated into two round sclerites, or fused to posterior one. Case (Figs 8B–8D). Case of final instar larva up to 2.8 mm, compressed laterally, composed of elongateellipsoidal right and left valves, made of fine mineral particles by larvae mainly found in stony bottom, or of organic materials by larvae found in hygropetric habitat. Organic cases made of diatoms only (Terpsinoe muninensis Tsuji 2018, species endemic to Ogasawara Islands), pieces of bryophyte only, or mixture of diatoms and pieces of bryophyte. Holotype. Male, Japan, Ogasawara Islands, Chichi-jima: Ishiura-kita (N27.0762, E142.2227, 220 m above sea level), 13.iv.2019, TI et al., S (CBM-ZI 0184758). Paratypes. 2 males, same data as holotype (CBM-ZI 0184759–0184760). Other specimens. Chichi-jima: 1 male, 3 pupae, 3 larvae, same data as holotype; 2 males, 2 females, type locality, 12–13.iv.2019, TI et al., S & H; 1 male, 4 pupae, Fukiage-dani, 14.iv.2019, TI &TS, S & H; 50 males, 5 females, 6 pupae, 8 prepupae, 10 larvae, same locality, 2.iii.2020, TI & CT, S & H; 2 males, 2 pupae, 3 larvae, Hatsuneura, 15.iv.2019, TI et al . Ani-jima: 6 males, 3 females, Takinoura-gawa, 3.iii.2020, TI et al., S. Remarks. The larva of this species is distinctive in having short wide dorsal sclerites of abdominal segment I. As far as we know, such dorsal sclerites of the segments have not been found in any congeneric species in North America (Ross 1944; Wiggins 1996), Australia (Wells 1985), Europe (Wallace et al. 2003; Waringer & Graf 2011), Angola (Wells & de Moor 2020), or Japan (Ito 2021). Absence of small spines on the dorsum of the head is also exceptional, since they are numerous and scattered in many species of Hydroptila larvae (Wells 1985; Ito 2021). Distribution (Figs 1B, 1C). Japan (Ogasawara Islands: Chichi-jima, Ani-jima). Habitat (Figs 8D–8F). Larvae of this species were found on both hygropetric habitat and stony bottoms in shallow water flows of small mountain streams. Sclerotized parts of larvae living on stony bottoms tend to be black and those in hygropetric habitat are a somewhat lighter color, dark brown. This species was often collected with H. demersa, but was more abundant than the latter. Etymology. The species epithet is an adjective referring to the name of the type locality. Japanese name. Ishiura-hime-tobikera., Published as part of 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, pp. 141-164 in Zootaxa 5231 (2) on pages 150-154, DOI: 10.11646/zootaxa.5231.2.2, http://zenodo.org/record/7576775, {"references":["Wiggins, G. B. (1996) Larvae of the North American Caddisfly Genera (Trichoptera), Second Edition. University of Toronto Press, Toronto, 457 pp. https: // doi. org / 10.3138 / 9781442623606","Wells, A. (1985) Larvae and Pupae of Australian Hydroptilidae (Trichoptera), with Observations on General Biology and Relationships. Australian Journal of Zoology, Melbourne, Supplementary Series, 113, 69. https: // doi. org / 10.1071 / AJZS 113","Tsuji, A. (2018) A new freshwater diatom, Terpsinoe muninensis sp. nov., from the Ogasawara Islands, Japan. Memoirs of the National Science Museum, Tokyo, 52, 5 - 15.","Ross, H. H. (1944) The caddisflies, or Trichoptera, of Illinois. Bulletin of the Illinois Natural History Survey, 23, 1 - 326. https: // doi. org / 10.21900 / j. inhs. v 23.199","Wallace, I. D., Wallace, B. & Philipson, G. N. (2003) Key to the case-bearing caddis larvae of Britain and Ireland. Freshwater Biological Association, Scientific Publication 61. Freshwater Biological Association, Liverpool, 259 pp.","Waringer, J. & Graf, W. (2011) Atlas of Central European Trichoptera Larvae. Erik Mauch Verlag, Dinkelscherbe, 468 pp.","Wells, A. & de Moor, E. C. (2020) Hydroptilidae (Trichoptera) of Angola, a new genus, seven new species, and five new records. Zootaxa, 4868 (4), 495 - 514. https: // doi. org / 10.11646 / zootaxa. 4868.4.2","Ito, T. (2021) Descriptions of final instar larvae of six species of the genus Hydroptila Dalman (Trichoptera, Hydroptilidae) in Japan. Zootaxa, 4905 (3), 339 - 350. https: // doi. org / 10.11646 / zootaxa. 4915.3.3"]}

Hydroptila tokoyo Ito & Sasaki sp. nov. (Figs 9H–9K, 10E) Diagnosis. The male of this species is similar to that of H. ogasawaraensis, but is distinguished from the latter by the length of the phallic apparatus, the presence of lateral plates of segment X, and the shape of inferior appendages; the anterior end of the phallic apparatus extends from abdominal segment VII when retracted, the lateral plates are absent, and the inferior appendages are without lateral humps in H. ogasawaraensis (Figs 9A–9D); the phallic apparatus extends from abdominal segment III when retracted, a pair of lateral plates is present, and each inferior appendage has a lateral hump in H. tokoyo (Figs 9H–9L). Male. Head, thorax, wing color, tibial spurs, processes of sternites V and VII are as for H. demersa. Forewings each 2.0– 2.1 mm in length and hind wings each 1.8–2.0 mm (n = 2). Antennae each 27–29-segmented, length 1.0– 1.2 mm long (n = 2). Male genitalia (Figs 9H–9L). Segment IX (IX) annular, its transverse tergal bridge narrow, its midline 1/3 as long as segment; with deep subquadrate margin dorsally; small, sclerotized, subrectangular, dark and setose plate (dsp IX) at posterodorsal margin, covered with very fine setae; deep and broad subtriangular excision on anterior margin ventrally. Dorsal plate (dp) semi-membranous, blunt apically in dorsal view, subtriangular in lateral view. Lateral plates (lp) subtriangular in lateral view, apically directed caudoventrad. Subgenital plate (sp) slightly sclerotized, gradually tapered, directed caudoventrad, with very small hook subapicoventrally. Inferior appendages (ia) thick, directed caudad, each with irregularly shaped lateral hump (lh) at basal 2/5 and hooked caudodorsad apically. Phallic apparatus very long, almost straight, anterior end extending from middle of segment III when retracted, with slender titillator at 4/5 length. Female, larva and case. Unknown. Holotype. Male, Japan, Ogasawara Islands, Chichi-jima: Tokoyo-gawa,Tokoyo-no-taki Waterfall (N27.0574, E142.2058, 30 m above sea level), 2.iii.2020, TI & CT, S (CBM-ZI 0184761). Paratypes. 1 male, same data as holotype (CBM-ZI 0184762). Other specimens. Chichi-jima: 1 male, same data as holotype; 1 male, type locality, 16.iv.2019, TI & CT, S; 1 pupa (male), a tributary of Tokoyo-gawa, upper reach, 19.iv.2022, TI & TS, H. Distribution (Fig. 1C). Japan (Ogasawara Islands: Chichi-jima). Habitat and remarks (Figs 10E, 10F). The males were collected from Tokoyo-no-taki Waterfall, covered with bryophytes and algae (Fig. 10E). Many Hydroptila larvae were there (Fig. 10F), but they couldn’t be identified at species level morphologically, since two species (H. tokoyo and H. ogasawaraensis) have been detected there by both morphological examination of males and DNA analyses of larvae. Japanese name. Tokoyo-hime-tobikera., Published as part of 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, pp. 141-164 in Zootaxa 5231 (2) on pages 154-157, DOI: 10.11646/zootaxa.5231.2.2, http://zenodo.org/record/7576775, {"references":["Ito, T., Ohkawa, A. & Hattori, T. (2011) The genus Hydroptila Dalman (Trichoptera, Hydroptilidae) in Japan. Zootaxa, 2801, 1 - 26. https: // doi. org / 10.11646 / zootaxa. 2801.1.1"]}

Hydroptila ogasawaraensis Species Group Ito Diagnosis. Males of this species-group are somewhat similar to those of the H. pulchricornis Species Group of Marshall (1979), a small Palearctic group, in having a short, subacute apicoventral process on abdominal sternite VII, relatively short and annular segment IX with a narrow (longitudinally short) dorsal bridge, and an almost straight and fine phallic apparatus, but they can be discriminated from the later by the length of the inferior appendages: The relative length of the appendages to segment IX is more than 1.0 in the H. pulchricornis Species Group (Marshall 1979; Ito et al. 2011), but 0.5–0.8 in this new H. ogasawaraensis Species Group. Final instar larvae of the H. ogasawaraensis Species Group are also similar to those of the H. pulchricornis Species Group, but differ from the later by the presence of dorsal chloride epithelia on abdominal segments I–VI or a depressed oblong head capsule; in contrast, the described larvae of the H. pulchricornis Species Group species have the chloride epithelia on segments II–VI and a roundish head capsule and include H. phenianica Botosaneanu 1970, H. dampfi Ulmer 1929, and H. oguranis Kobayashi 1974 (Ito 2021). Male: Pair of anterolateral processes of sternite V each with two setae, one long and one short; sternite VII with short, subacute, ventral process; segment IX short, annular with narrowly transverse dorsal bridge; phallic apparatus almost straight; and inferior appendages moderately short. Final instar larva: Small dorsal sclerites or small dorsal chloride epithelia on abdominal segments I–VI or with depressed, oblong head capsule. Species belonging to the Group: Hydroptila ogasawaraensis, H. demersa sp. nov., H. ishiura sp. nov., H. tokoyo sp. nov., H. hahajima sp. nov., and H. nagahama sp. nov. All species are endemic to the Ogasawara Islands. Remarks: Larval morphology differs greatly between H. demersa and the other five species, but the molecular phylogeny suggests that they all belong to the same species group (Fig. 2). Japanese name: Ogasawara-himetobikera-shugun., Published as part of 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, pp. 141-164 in Zootaxa 5231 (2) on pages 160-161, DOI: 10.11646/zootaxa.5231.2.2, http://zenodo.org/record/7576775, {"references":["Marshall, J. E. (1979) A review of the genera of the Hydroptilidae (Trichoptera). Bulletin of the British Museum (Natural History), 39, 135 - 239.","Ito, T., Ohkawa, A. & Hattori, T. (2011) The genus Hydroptila Dalman (Trichoptera, Hydroptilidae) in Japan. Zootaxa, 2801, 1 - 26. https: // doi. org / 10.11646 / zootaxa. 2801.1.1","Botosaneanu, L. (1970) Trichopteres de la Republique Democratique-Populaire de la Coree. Annales Zoologici Warszawa, 27 (15), 275 - 359.","Ulmer, G. (1929) Uber einige deutsche Hydroptiliden. Zoologischer Anzeiger, 80, 253 - 266. https: // doi. org / 10.1002 / mmnd. 48019290302","Kobayashi, M. (1974) On two new species of Hydroptilidae from Japan (Insecta: Trichoptera). Bulletin of the Kanagawa Prefectural Museum Natural Science, 7, 67 - 70.","Ito, T. (2021) Descriptions of final instar larvae of six species of the genus Hydroptila Dalman (Trichoptera, Hydroptilidae) in Japan. Zootaxa, 4905 (3), 339 - 350. https: // doi. org / 10.11646 / zootaxa. 4915.3.3"]}