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DNA-based studies have revealed that the terrestrial water scavenger beetle genus Cercyon Leach, 1817 (Coleoptera: Hydrophilidae: Sphaeridiinae: Megasternini) is polyphyletic, grouping similarly looking but unrelated species that were not assigned to other genera due to the absence of unusual morphological characters. In this study, we analyse the morphology, DNA data and species diversity of one of the Asian clades of ' Cercyon ' to test whether a natural, phylogeny-based generic classification can be established. We add DNA data (five nuclear and three mitochondrial fragments) for additional species and specimens of the clade to test its monophyly and reveal phylogenetic relationships among species. We perform a detailed morphological study of all species, including SEM micrographs, to reveal synapomorphies of the DNA-based clades. We demonstrate that the lineage, described here as Asiacyon Mai, Jia, Ryndevich & Fikáček, gen. nov., is strongly supported by DNA data, has limited distribution (eastern Asia), and its species share similar biology (inhabiting fresh or decaying plant tissues), though it can be only diagnosed by a combination of plesiomorphic characters. A detailed treatment is provided for the Chinese species, including species diagnoses, illustrations of habitus and male genitalia, (re)descriptions and a key to species. A total of 14 Chinese species are recognised, of which 11 are described as new: Asiacyon pax sp. nov. (Guangdong, Hong Kong, Hunan), A. pseudincretus sp. nov. (Anhui, Jiangxi, Taiwan, Zhejiang), A. vicincretus sp. nov. (Guangdong, Guangxi), A. zhengyucheni sp. nov. (Yunnan), A. huilanae sp. nov. (Yunnan), A. cornipenis sp. nov. (Yunnan), A. belousovi sp. nov. (Yunnan), A. liangchengi sp. nov. (Yunnan), A. paraequalis sp. nov. (Yunnan), A. pengzhongi sp. nov. (Hunan) and A. xiuzhenae sp. nov. (Hainan, Yunnan). Three Chinese species previously classified in Cercyon are transferred to Asiacyon : A. incretus (d'Orchymont, 1941), comb. nov., A. primoricus (Ryndevich & Prokin, 2017), comb. nov. (newly recorded from China) and A. indicus (d'Orchymont, 1926), comb. nov. (newly recorded from China and Laos). Additionally, seven Asian species previously classified in Cercyon are transferred to Asiacyon based on their external morphology, but not studied in detail: A. aequalis (Sharp, 1884), comb. nov., A. conjiciens (Walker, 1858), comb. nov., A. dilutus (Régimbart, 1903), comb. nov., A. placidus (Sharp, 1884), comb. nov., A. pseudodilutus (Satô, 1979), comb. nov., A. retius (Ryndevich & Prokin, 2017), comb. nov., and A. rubicundus (Sharp, 1884), comb. nov. In total, the genus now comprises 21 named species and several undescribed species from India, Myanmar and Indonesia. ZooBank: Morphology is not always a good indicator of biological diversity, aswe illustrate in Asian species classified under Cercyon , a genus of terrestrial water scavenger beetles. We describe Asiacyon gen. nov., which is strongly supported by DNA data, has limited distribution and unique habitat preferences, yet it highly resembles other unrelated ʻ Cercyon ʼ. The species diversity of this lineage was under-estimated: we describe 11 new species from China. We argue that ' Cercyon ' should be divided into DNA-based natural genera despite their morphological similarity. (Image credit: Martin Fikáček.) [ABSTRACT FROM AUTHOR]

The New Zealand endemic beetle genus Saphydrus Sharp, 1884 (Coleoptera : Hydrophilidae : Cylominae) is studied in order to understand its phylogenetic position, species-level systematics, biology and distribution, and to reveal reasons for its rarity. The first complete genus-level phylogeny of Cylominae based on two mitochondrial (cox1 , 16S) and two nuclear genes (18S, 28S) covering 18 of 19 genera of the subfamily reveals Saphydrus as an isolated lineage situated in a clade with Cylorygmus (South America), Relictorygmus (South Africa) and Eurygmus (Australia). DNA is used to associate two larval morphotypes with Saphydrus : one of them represents the larvae of S. suffusus Sharp, 1884; the other, characterised by unique characters of the head and prothorax morphology, is revealed as sister but not closely related to Saphydrus. It is described here as Enigmahydrus , gen. nov. with a single species, E. larvalis , sp. nov., whose adult stage remains unknown. Saphydrus includes five species, two of which (S. moeldnerae , sp. nov. and S. tanemahuta , sp. nov.) are described as new. Larvae of Enigmahydrus larvalis and Saphydrus suffusus are described and illustrated in detail based on DNA-identified specimens. Candidate larvae for Saphydrus obesus Sharp, 1884 and S. tanemahuta are illustrated and diagnosed. Specimen data are used to evaluate the range, altitudinal distribution, seasonality and population dynamics over time for all species. Strongly seasonal occurrence of adults combined with other factors (winter occurrence in S. obesus , occurrence at high altitudes in S. tanemahuta) is hypothesised as the primary reason of the rarity for Saphydrus species. By contrast, Enigmahydrus larvalis underwent a strong decline in population number and size since the 1970s and is currently known from a single, locally limited population; we propose the 'nationally threatened' status for this species. http://zoobank.org/urn:lsid:zoobank.org:pub:28D87163-29E8-418C-9380-262D3038023A The New Zealand fauna is highly endemic, with many species only known from their type series. Moreover, threat through habitat loss, agriculture, climate change and the introduction of alien species drive the decline of species including the little-known ones. Our study reports on the systematics and distribution of the hydrophilid genera Saphydrus and Enigmahydrus , gen. nov. and analyses whether their rare occurrence may be due to human impact. Morphology of adult and immature stages is studied in detail and the taxa are placed into a phylogenetic context. [ABSTRACT FROM AUTHOR]