Hydroscapha shuihau, Fikáček & Hu & Aston & Jia & Liang & Liu & Minoshima, 2020

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 : 344

Hydroscapha shuihau , new species

Material examined. Holotype: male ( NMPC): Hong Kong, Lantau , Shui Hau, coordinates, 22.220250°N, 113.916434°E, 14 April 2019, coll. P. Aston, washed out of small layer of slime in mud . Paratypes: 16 exs. ( NMPC, SYSU, NMNS): same label data as the holotype ; 14 exs. ( NMPC, SYSU, PCPA, AFCD): same locality, 16 November 2013, coll. P. Aston ; 18 exs. ( PCPA): same locality, 5 November 2017, coll. P. Aston ; 1 ex. ( PCPA): same locality, 10 December 2013, coll. P. Aston.

Diagnosis of adult. Hydroscapha shuihau , new species, is very similar to H. hunanensis known from Central China (Hunan). However, it is easily distinguished by the shape of the female tergite VI and sternite VI, which are both only weakly narrowing posteriad (they are both strongly narrowed in the posterior third and projecting as a narrowly rounded posterior portion in H. hunanensis ). Slight differences may be also found in the shape of the aedeagus (wider basally and evenly arcuate in apical half in H. shuihau , narrower basally and nearly straight in apical half except the apex in H. hunanensis ) and in proportions of the terminal antennomere (relatively wider in H. shuihau than in H. hunanensis ) and the mesoventral elevation (relatively shorter in H. shuihau than in H. hunanensis ). For the differences between H. shuihau and H. takahashii , see under the latter species.

Using the keys by Fikáček & Šípková (2009), males of H. shuihau key to H. hunanensis , and females to H. coomani , H. hunanensis , and H. reichardti (which were keyed out together due to absence of distinguishing characters). It differs from H. coomani Löbl, 1994 , in the shape of the male sternite V, which is weakly sinuate on the posterior margin (with a pair of pointed lobes in H. coomani , compare Fig. 4E to Löbl, 1994: fig. 17). It differs from H. reichardti in male sternite V lacking two distinctly separate tufts of setae (vs. two tufts in H. reichardti , compare Fig. 4E with Löbl, 1994: fig. 54). Both H. coomani and H. reichardti are also slightly larger than H. shuihau (with the length of forebody ranging 0.85–0.94 mm, compared to 0.70–0.75 mm in H. shuihau ). Major diagnostic characters are listed in Tables 2 and 3 to be compared with those of other Asian species listed by Fikáček & Šípková (2009).

Description of adult ( Figs. 3 F–J, 4D–F). Total body length: 1.0– 1.1 mm. Length of forebody (from anterior margin of head to posterior margin of elytra): 0.70–0.75 mm. Dorsal colouration reddish brown to dark brown. Labrum angularly excised anteriorly, with two groups of setae dorsally. Antenna ( Fig. 4D ) with short antennomere III (= second visible) and widely elongate asymmetrical antennomere IX (= ultimate one); the latter with few apical sensilla. Mesoventral elevation subpentagonal, 2.1× wider than long ( Fig. 4F ).

Male. Protarsus with sucking disc on basal tarsomere. Posteroventral margin of abdominal segment V weakly sinuate, ventral surface with longer setae indistinctly subdivided into two groups ( Fig. 4E ). Tergite VI widely rounded on posterior margin. Sternite VI without tufts of hairs. Sternite VII ( Fig. 3G ) with small medioposterior projection. Tergite VII ( Fig. 3H ) weakly convex posteromesally. Aedeagus ( Fig. 3F ) wide basally, arcuate in posterior two thirds, gradually narrowing towards apex.

Female. Protarsus without suckers. Abdominal sternite VI ( Fig. 3I ) widely subtriangular, tergite VI ( Fig. 3J ) widely rounded posteriorly.

Etymology. The new species is named after the village of Shui Hau on Lantau Island where the species was found. Noun in apposition.

Distribution. The species is only known from Lantau Island in Hong Kong.

Bionomics ( Fig. 8D, E ). At the type locality, the beetles have been found in filamentous algae in a hygropetric environment on the concrete footpath leading from Shui Hau village to the sea. The footpath is edged by a freshwater marsh on both sides, which is mainly grassy and grazed by water buffalo. The beetles only occur in the hygropetric areas where the footpath has sunken and is covered by a very thin, almost stagnant film of water over a thin layer of mud and the filamentous algae. The beetles are usually present from November to April (mostly in the dry season) when the slope of the marsh allows the hygropetric environment to flourish. The algae die off before the hot summer months and again start to form mats in September; despite this, the beetles were not present until 9 November 2019, even though the filamentous mats of algae were fairly large (80 cm 2). We did not find any beetles in similar-looking habitats in areas situated close to the agricultural land or closer to the sea. The specimens were collected from the green algae together with Sphaerius sp. ( Sphaeriusidae ), Hydraena sp. ( Hydraenidae ), and various Hydrophilidae including Enochrus (Methydrus) esuriens Walker, 1858 , and Paracymus sp. Unfortunately, during the autumn of 2019, material was taken out of the marsh, causing the marsh level to drop by 30 cm, resulting in the drying of the hygropetric areas, and by the end of January 2020 all the areas where the beetles were previously found, were totally dry. No specimens of Hydroscapha were found in the winter of 2019–2020.

Figures

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. 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. 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.