Hydroyixia Fikáček & Prokin & Yan & Yue & Wang & Ren & Beattie 2014, GEN. NOV.
Creators: name: Fikáček, Martin
name: Prokin, Alexander
name: Yan, Evgeny
name: Yue, Yanli
name: Wang, Bo
name: Ren, Dong
name: Beattie, Robert
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Hydroyixia

description: HYDROYIXIA GEN. NOV.   Type species: Hydroyixia elongata sp. nov., by present designation.   
 Time range: Early Cretaceous.   
 Diagnosis: Body medium-sized; labrum partly exposed in dorsal view (Figs 5A, D, F, 7J, 8E); anterior margin of clypeus deeply and widely excised mesally (Figs 5A, D, F, 7J, 8E); prosternum moderately long; scutellar shield small, triangular; anapleural sutures well developed, weakly curved, converging anteriad; mesoventrite very narrow anteriorly (Figs 5B, I, 7I, K, 8F); mesocoxae very narrowly separated; abdomen with five ventrites; apical abdominal ventrite with shallow wide emargination (Figs 5B, F–G, I, 7L–M); elytron with deeply impressed sutural stria (Figs 5A, C, F, I); elytra with series of punctures (Figs 5C, F, I); elytral trichobothria very distinct (Fig. 5E); metathoracic leg with five tarsomeres; mesotarsomere 1 very short (Fig. 5H).   
 Etymology: The generic name consists of the prefix hydro - referring to the Hydrophilidae, and the ending -yixia referring to the Yixian Formation from which both species of this genus are described. Feminine.   
 Family assignment: The combination of large clypeus, well-developed frontoclypeal sutures reaching lateral margin of head closely before eyes, head not constricted behind eyes, and the small triangular scutellar shield assigns the fossil reliably to the family Hydrophilidae s.s. Additionally, it corresponds well with the modern aquatic groups of the Hydrophilidae in general habitus, ventral morphology, and the presence of very distinct trichobothria on elytra and pronotum.   
 Comparison with other hydrophilid genera: Based on the presence of the apical emargination on the posterior margin of the abdominal ventrite 5, Hydroyixia resembles the extant representatives of the Hydrobiusini, early branching Hydrophilini, Enochrinae, and Acidocerinae. In contrast to the Hydrophilini, the meso- and metaventrite of Hydroyixia are not fused into a common ventral keel and the posterior leg lacks series of swimming hairs. In contrast to the Cymbiodyta clade of the Enochrinae, the metathoracic leg bears five tarsomeres. The mesoventrite narrowing anteriad is not known in any extant genus of the Enochrinae, and in the Acidocerinae only occurs in few clades of the Helochares group (e.g. genus Peltochares Régimbart, 1907 and Helochares obscurus species group, from which Hydroyixia gen. nov. differs by the presence of the sutural stria). Angular excision of the clypeus is present in the sperchopsine clade of the Hydrobiusini (which differ from Hydroyixia by denticulate lateral margins of elytra) and in many genera of the Acidocerinae. Many aquatic taxa of the Acidocerinae are also characterized by very conspicuous trichobothria on pronotum and elytra, which corresponds to some specimens of Hydroyixia. The combination of characters present in Hydroyixia hence assigns it best to the Acidocerinae.
description: Published as part of Fikáček, Martin, Prokin, Alexander, Yan, Evgeny, Yue, Yanli, Wang, Bo, Ren, Dong & Beattie, Robert, 2014, Modern hydrophilid clades present and widespread in the Late Jurassic and Early Cretaceous (Coleoptera: Hydrophiloidea: Hydrophilidae), pp. 710-734 in Zoological Journal of the Linnean Society 170 (4) on page 722, DOI: 10.1111/zoj.12114, http://zenodo.org/record/10273948