Hydroptila ishiura 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 : 150-154

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.

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 3. Male of Hydroptila demersa sp. nov. 3A, habitus, dorsal; 3B, head and thorax, dorsal; 3C, head, right lateral; 3D, abdominal segments I–X, left lateral, with enlargement figures of anterolateral process (paired) of sternite V and posteroventral process of sternite VII; 3E, genitalia, left lateral; 3F, same, dorsal; 3G, same, ventral; 3H, phallic apparatus, left lateral. Abbreviations: IX = abdominal segment IX; dh = dorsolateral hump; dp = dorsal plate; ia = inferior appendage (paired); lap = labial palpus (paired); map = maxillary palpus (paired); pa = phallic apparatus; sp = subgenital plate.

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 7. Larva of Hydroptila ishiura sp. nov. 7A, habitus, right lateral; 7B, habitus, dorsal; 7C, head, ventral; 7D, right antenna, right lateral; 7E, right foretrochantin and foreleg, right lateral; 7F1–7F3, abdominal segment I, dorsal, variations; 7G, anal claw, right lateral (paired). 8, 9 = primary setae 8 and 9 (Wiggins 1996).

FIGURE 8. Habitat and habitus views of adult, larva, and case of Hydroptila ishiura sp. nov. 8A, adult habitus on leaf of riparian tree; 8B, larva and case in hygropetric habitat, left lateral; 8C, same, enlargement of small section of case showing piece of bryophyte (a) and diatom (b); 8D, larvae with cases on rock, dorsal; 8E, hygropetric habitat at type locality; 8F, stony stream habitat at Takinoura-gawa, Ani-jima.