Hydroscapha takahashii Miwa, 1935

Fikáček, Martin, Hu, Fang-Shuo, Aston, Paul, Jia, Feng-Long, Liang, Wei-Ren, Liu, Hsing-Che & Minoshima, Yûsuke N., 2020, Comparative morphology of immature stages and adults of Hydroscapha from Taiwan, with description of a new species from Hong Kong (Coleoptera: Myxophaga: Hydroscaphidae), Raffles Bulletin of Zoology 68, pp. 334-349 : 336-344

Hydroscapha takahashii Miwa, 1935

Hydroscapha takahashii Miwa, 1935: 352 .

Hydroscapha takahashii – Löbl, 1994: 32; Jäch, 1995: 33; Fikáček & Šípková, 2009: 43–45.

posterior margin mesally convex straight convex

arrangement of posterolateral setae serial irregular irregular

median part projecting weakly no weakly

of

tufts hairs no no no

posterior margin granulate no no no

)

.

posterior margin weakly sinuate weakly sinuate weakly sinuate

2009

,

Šípková & chaetotaxy two indistinctly tufts divided two distinctly tufts divided two indistinctly divided tufts

Fikáček

in view

from shape lateral arcuate straight straight

adapted

(at face

sclerites angulate dorsal no no no

abdominal

and bent ventrad apically no no yes

genitalia

of

male

subapical region

in view lateral narrow narrow narrow

Characters

.

2

Species shuihau

,

species takahashii hunanensis Table H. new H. H.

Type material examined. Syntypes: 1 male ( TARI): “ Shinten / Formosa / 14-VII.1935 [14 July 1935] / R. Takahashi // Hydroscapha / takahashii / Miwa / DET. Y. MIWA // 3056 // TYPE” ; 2 females ( TARI): “ Shinten / Formosa / 14-VII.1935 [14 July 1935] / R. Takahashi // Hydroscapha / Takahashii / Miwa / DET. Y. MIWA” ; 2 females ( TARI): “ Shinten / Formosa / 14-VII.1935 [14 July 1935] / R. Takahashi // Hydroscapha / Takahashii / Miwa / DET. Y. MIWA” .

Additional material examined. 365 adults, 251 larvae, 15 pupae ( NMPC, BMNH, KMNH, NCHU, NHMW, NMNS, SYSU, TARI): Taiwan: Nantou County, Heshe, Xinyi Township Tongfu Village; at bridge over Zhenyoulanxi , 23.58767°N, 120.89027°E, 16 May 2018, coll. Fikáček et al. (2018-TW35a), on exposed concrete wall with thin layer of flowing water and a layer of green algae. 9 adults ( NMPC): Taiwan: New Taipei, Wulai City at Wulai Bridge , 24.86404°N, 121.5518°E, 05 and 18 May 2018; coll. Chang et al. (2018-TW09), seepage on concrete wall next to the Laka Rd. , partly overgrown by the layer of algae . 1 male ( NCHU): Taiwan: Kaohsiung City, Jingualiao bridge, Neiman Township , 16 April 2019 , 23.0122700°N, 120.5207176°E, in stream, by net, coll. K-Y Zheng. 2 males ( NCHU): Taiwan: Taichung City, Xiannv Waterfall, Taiping District , 24.1216°N, 120.8181°E, 04 January 2020, coll. H.-C. Liu. 210 adults, 9 larvae ( FSHC): Taiwan: Taichung City, Tonglin, Wufeng District , 24.0712°N, 120.7524°E, 23 April 2020, coll. F.-S. Hu.

Type locality. Formosa , Shinten in Taihoku Province [= Taiwan, Xindian] .

Diagnosis of adults. Males are most similar to H. reichardti Löbl, 1994 from Sulawesi in the following characters: two clearly divided tufts of setae on sternite V, sternite VI lacking lateral tufts of hairs, posterior margin of sternite VII only weakly convex, aedeagus evenly curved and narrowing towards apex, and proportions of antennomeres III and IX; they differ from H. reichardti in a slightly smaller body (forebody 0.69–0.76 mm in H. takahashii , 0.85–0.94 mm in H. reichardti ) and a more elongate apex of the aedeagus (compare Fig. 3A with Löbl, 1994: fig. 55). Females are most similar to H. jumaloni Satô, 1972 from the Philippines in the following characters: simple posterior margin of sternite VI, slightly projecting posterior margin of tergite VI, and smaller body size. They differ from H. jumaloni in a sinuate posterior margin of female sternite V (straight in H. jumaloni ). Males of H. takahashii may be distinguished from those of H. shuihau , new species, and H. hunanensis by distinctly divided tufts of setae on sternite V, sternite VI lacking median projection, and tergite VII being straight posteromedially. Females of H. takahashii may be distinguished from these species by a distinctly triangular (and hence pointed) posterior margin of tergite and sternite VI. The main diagnostic characters are listed in Tables 2 and 3 to be compared with those of other Asian species as listed by Fikáček & Šípková (2009).

Redescription of adults ( Figs. 2D , 3 A–E, 4A–C). Total body length: 1.0– 1.2 mm. Length of the forebody (from

anterior margin of head to posterior margin of elytra): 0.69–0.76 mm. Dorsal colouration reddish-brown to dark brown. Labrum angularly excised anteriorly, with two groups of setae dorsally. Antenna ( Fig. 4A ) with moderately long antennomere III (= second visible) and narrowly elongate slightly asymmetrical antennomere IX (= ultimate one); the latter with few apical sensilla. Mesoventral elevation subpentagonal, 2.0× wider than long ( Fig. 4C ).

Male. Protarsus with one sucking disc on basal tarsomere. Posteroventral margin of abdominal segment V weakly sinuate, ventral surface with two groups of setae distinctly separated from each other ( Fig. 4B ). Tergite VI truncated on posterior margin. Sternite VI without tufts of hairs. Sternite VII ( Fig. 3B ) without medioposterior projection. Tergite VII ( Fig. 3C ) entire posteromesally. Aedeagus ( Fig. 3A ) narrow basally, nearly straight in posterior two thirds, gradually narrowing towards apex.

Female. Protarsus lacking sucking disc. Abdominal sternite VI ( Fig. 3D ) and tergite VI ( Fig. 3E ) both triangularly pointed posteriorly.

Morphology of last instar larva ( Figs. 2A , 5 , 6 ). Body. Total length: 1.65–1.75 mm. Larva narrowly elongate. Legs largely hidden under body in dorsal view. Head. Width of head capsule: 0.29–0.30 mm. Head transverse, bearing fine dorsal microsculpture ( Fig. 5C ). Five pigmented spots

(stemmata) are situated at side of head: four of them have lens-like cuticular structure ( Fig. 5A : st), the fifth is not associated with lens-like structure. Genae projecting in wide genal folds ( Fig. 5A, B : ge) bearing stout setae directed upwards; these folds adjoin lateral sides of labrum, together completely concealing mouthparts in dorsal and lateral views. Labrum fused with clypeus ( Fig. 5A : lb), deeply concave on anterior margin ( Fig. 5B : lb). Mandible not projecting, robust basally, with thin multidentate apex ( Fig. 5E : md). Maxilla robust basally, apically projecting into narrow multidentate mala ( Fig. 5E : mx). Labium largely covering mouthparts in ventral view; ligula large and robust ( Fig. 5E : lig), bearing numerous specialised sensilla (‘papilae’, Fig. 5E : pa); labial palp with two palpomeres, lateral sensorial appendage with longitudinally ridged microsculpture ( Fig. 5D : SA). Thorax. Each thoracic segment dorsally with large sclerite not subdivided mesally; surface with microsculpture similar to that on dorsal surface of head; anterior and posterior margins of protergum and posterior margins of meso- and metatergum bearing transverse row of setae ( Fig. 6B ), setae on lateral margins much longer than posterior ones; additional short setae also on disc, especially in mesal area. Pleural areas weakly sclerotised, with fine microsculpture ( Fig. 6I, L ). Sternal portion very narrow between closely adjacent articulations of legs ( Fig. 6L ). Legs ( Fig. 6I ) tetramerous, with large elongate coxa, long femur (likely fused basally with trochanter), relatively short tibiotarsus, and one long simple claw. Abdomen with 10 segments ( Fig. 6A ). Segments III–IX with tergite and sternite fused into complete ring ( Fig. 6A, J, K ). Sclerites of segments I–VIII with fine microsculpture, series of long setae at posterior margin, and transverse series of stouter but more sparsely arranged setae slightly anterior to posterior margin ( Fig. 6J, K ). Segment X exposed as ventrally facing sclerotised plate with pair of hooks ( Fig. 6G, H ). Spiracles balloon-like ( Fig. 6 C–F), with fine walls enforced internally by longitudinal ridges, situated on posterolateral margin of protergum, laterodorsal part of abdominal segment I, and laterally on abdominal segment VIII. Thoracic spiracle ca. 2.5× as long as wide, on very short projection; spiracle on abdominal segment I ca. 2.5× as long as wide, on low wide tubercle; spiracle on abdominal segment VIII ca. 3.5× as long as wide, in a long finger-like projection.

Morphology of pupa ( Figs. 2B, C , 7 ). Pupa short and wide, obtect, in natural condition resting within last larval exuvia ( Fig. 2B, C ). Head with exposed antennae, antenna with exposed scapus. Legs nearly completely covered by wingsheaths. Abdominal segments I–III dorsally flat, with lateral portions projecting anteriorly (segment I), laterally (segment II), and dorsally (segment III), apex of each lobe with open spiracle ( Fig. 7D, E ). Abdominal segments III–VII ring-like, segment IV with laterally situated open spiracle on small ventrally directed tubercle ( Fig. 7G ). Segments VIII–X minute ( Fig. 7C, H ).

Remarks on adult morphology. Hydroscapha takahashii was originally distinguished from other Hydroscapha by the presence of the median furrow on the pronotum as stated

in the original description ( Miwa, 1935). As no specimens were available for study, this character was adopted by Löbl (1994) and Fikáček & Šípková (2009). However, the pronotum of H. takahashii is in fact smooth, and does not bear any furrow or impression ( Fig. 2D ), a feature shared by all other known Hydroscapha species. The first couplet in the keys by Löbl (1994) and Fikáček & Šípková (2009) is hence incorrect and has to be discarded.

Distribution. Endemic in Taiwan, but apparently widespread on the island. Presently, this species is known from five

lowland localities in northern (New Taipei City), central (Nantou County, Taichung City), and southern Taiwan (Kaohsiung City). The newly collected specimens studied in detail and sequenced are from Wulai which is situated ca. 12 km south of the type locality. In this regard, this species is similar to other aquatic beetles in Taiwan associated with streams and rivers, which, even if they are widespread lowland species, are often endemic (e.g., Jäch, 1998; Jäch & Díaz, 1998; Fikáček & Liu, 2019).

Bionomics ( Fig. 8 A–C). In Wulai and Heshe, beetles were found on a wet concrete vertical wall with a small amount of very slow-flowing water, partly or entirely covered by algae. In Wulai (ca. 150 m a.s.l.), a small amount of algae was present and a low density of Hydroscapha adults; we did not find immature stages. Oocyclus and Agraphydrus hydrophilid beetles were collected from the same habitat. In Heshe (ca. 800 m a.s.l.), the habitat was completely covered with algal mats mixed with sandy mud. Numerous adults, all larval instars and pupae of H. takahashii were collected, together with adults and larvae of Laccobius cf. hammondi Gentili ( Hydrophilidae , Coleoptera ), adults and larvae of Saldoida sp. ( Saldidae , Hemiptera ), and larvae of Chironomidae , Dixiidae, and Psychodidae (Diptera) . After the discovery of the locality on 16 May 2018, the authors (Hu & Liu) visited it again on 14 October 2018, but the habitat was found dry and no more beetles were found. The specimen from Neiman Township was collected with a net in a small stream; it is likely a specimen washed out from the side of the stream. In Wufeng, mass occurrence of adults and few larvae were found in algal mats at the muddy banks of a small stony river ( Fig. 8F ).

Figures

Fig. 3. Genitalia and terminal abdominal sclerites of Hydroscapha takahashii (A–E), H. shuihau, new species (F–J), and examined paratypes of H. hunanensis (K–O). A, F, K, aedeagus in lateral view; B, G, L, male sternite VII; C, H, M, male tergite VII; D, I, N, female sternite VI; E, J, O, female tergite VI. Only sclerites showing differences among species are illustrated. For illustrations of all taxonomically important sclerites see https://zenodo.org/deposit/3537900.

Fig. 2. Habitus of larva, pupa, and adult of Hydroscapha takahashii. A, last-instar larva in dorsal view; B, C, pupa in larval exuviae (B, in dorsal view; C, lateral view); D, adult in dorsal view.

Fig. 4. External diagnostic characters of Hydroscapha takahashii (A–C), H. shuihau, new species (D–F), and H. hunanensis (G–I). A, D, G, antenna; B, E, H, male abdominal apex in ventral view with groups of setae on sternite V; C, F, I, mesoventral elevation.

Fig. 5. Head morphology of the third instar larva of Hydroscapha takahashii, SEM micrographs. A, head in lateral view; B, head in ventral view; C, dorsal sculpture of the head; D, detail of labial palpus; E, detail of mouthparts in ventral view. Abbreviations: an, antennal articulation (antenna broke up); ge, genal lobe; lb, labrum; md, mandible; mx, maxilla; lig, ligula; pa, ‘papilae’, specialised sensilla of the ligula; SA, sensorial appendage of the labial palpus; st, stemma. For high resolution micrographs see https://zenodo.org/deposit/3537900.

Fig. 6. Morphology of the third instar larva of Hydroscapha takahashii, SEM micrographs. A, whole larva in lateral view; B, detail of lanceolate setae on posterior margin of protergum; C, thoracic spiracular gill; D, spiracular gill of abdominal segment I; E, broken spiracular gill of abdominal segment VIII showing its internal structure; F, spiracular gill of abdominal segment VIII; G, abdominal apex with abdominal hooks, lateral view; H, abdominal apex, ventral view; I, meso- and metathoracic leg; J, detail of abdominal segments, dorsal view; K, detail of abdominal segments, ventral view; L, head, thorax, and abdomen in ventral view. Abbreviations: ah, abdominal hooks. For high resolution micrographs see https://zenodo.org/deposit/3537900.

Fig. 7. SEM micrographs of the pupa of Hydroscapha takahashii. A–C, habitus (A, ventral view; B, dorsal view; C, lateral view). D, E, details of lateral lobes of abdominal segments I–III with spiracles; F, detail of lateral portions of abdomen, ventral view; G, detail of spiracle on abdominal segment IV; H, abdominal apex, dorsal view. For high resolution micrographs see https://zenodo.org/deposit/3537900.

Fig. 8. Habitats of Hydroscapha in Taiwan and Hong Kong. A–C, mass occurrence of H. takahashii in Taiwan, Heshe: A, detail of living beetles in algal mat at wet concrete wall; B, wet concrete wall with algae at sides of Zhenyoulanxi river; C, view of algal mat showing numerous adults and larvae. D, E, type locality of H. shuihau, new species, in Hong Kong: D, general view of marsh below Shui Hui village, with small seeps at concrete trail; E, microhabitat at sides of concrete trail from where beetles were collected; F, algal mats at side of a small river in Taiwan: Wufeng, with mass occurrence of H. takahashii.