Agraphydrus Régimbart, 1903

Komarek, Albrecht & Hebauer, Franz, 2018, Taxonomic revision of Agraphydrus Régimbart, 1903 I. China and Taiwan (Coleoptera: Hydrophilidae: Acidocerinae), Zootaxa 4452 (1), pp. 1-101 : 17-18

Agraphydrus Régimbart, 1903

Agraphydrus Régimbart 1903c: 33 . Type species: Agraphydrus punctatellus Régimbart, 1903

Gymnhelochares Orchymont 1932: 692 . Type species: Helochares geminus ( Orchymont, 1932)

Pseudohelochares Satô 1960: 76 . Type species: Pseudohelochares narusei ( Satô, 1960) ; Satô 1965: 128

Pseudopelthydrus Jia 1998: 225 ff. Type species: Pseudopelthydrus longipalpus ( Jia, 1998) ; Komarek 2003: 384 Megagraphydrus Hansen 1999: 137 . Type species: Megagraphydrus siamensis ( Hansen, 1999) ; Minoshima et al. 2015: 7

Subgeneric classification. Gymnhelochares Orchymont, 1932 was described as a subgenus of Helochares Mulsant, 1844 based on two Oriental species, at a time when Agraphydrus was also considered by Orchymont (1932) a subgenus of Helochares . A third species was added to Gymnhelochares by Balfour-Brown (1958). Satô (1965) re-established Agraphydrus as separate genus, and Hansen (1991) transferred Gymnhelochares as a “provisional” subgenus to Agraphydrus .

Reduced meso- and metafemoral pubescence was considered as distinguishing feature for Gymnhelochares by Orchymont (1932). In many new species this character revealed to be clinal, and highly reduced femoral pubescence is present in species which are otherwise very different. For the subgenus Agraphydrus s. str. a unique diagnostic character has never been proposed and could not be identified in the present study. Consequently, this taxon should be regarded as paraphyletic. This implies that the previously used subgeneric subdivision of Agraphydrus is phylogenetically unjustified. Gymnhelochares is therefore synonymized with Agraphydrus s. str.

Systematic punctures. The distinction between two kinds of elytral punctures arranged in rows can be traced back to Régimbart (1901) who observed “séries principales” and “séries accessoires” on the elytra of hydrophilids. Régimbart (1903a, 1903b, 1904) applied the term “séries systématiques” and “points systématiques” for pronotal punctures arranged in certain patterns. Orchymont (1911, 1913, 1921, 1922, 1927, 1929, 1932, 1942) used the term “séries systématiques”, “pores systématiques”, “systematische Porenreihen” describing the appearance and position of these punctures on head, pronotum and elytra in different hydrophilid taxa. Hansen (1991) readopted and redefined the concept of “systematic punctures”, recognizing the necessity to differentiate between systematic punctures and “primary” serial elytral punctures. Oliva (1922) observes three kinds of elytral punctures: “hairs borne on granules or inserted in punctures”, “trichobothria”, and “micropores”. Systematic puctures are considered “trichobothria” also by Short (2008) and Short & Fikáček (2013). Short (2008) distinguishes between ground punctation, serial punctures and systematic punctures. Electron microscopic investigations ( Oliva 1992, Short 2008, Fikáček et al. 2012) revealed a characteristic structure of the systematic punctures bearing a very fine seta, often damaged and hardly to detect in dried specimens, probably serving as mechanoreceptors ( Fikáček et al. 2012) in the aquatic environment. Systematic punctures can be detected by their position ( Hansen 1991) and arrangement, they can “usually be easily detected as vestiges on the ventral face of the elytra”. Following the criteria of quality and position ( Remane 1952, 1961), I consider systematic punctures as homologue structures.

In most species of Agraphydrus four rows of systematic punctures are discernible on the elytra. In A. attenuatus , A. insidiator , A. politus , and A. puzhelongi a differentiation between systematic and serial punctures is not possible. In these cases we use the mere descriptive formulation “coarse punctures in rows”.

A full redescription of the genus Agraphydrus will be provided in one of the forthcoming contributions.

Diagnosis. Agraphydrus belongs to the subfamily Acidocerinae ( Short & Fikáček 2013), together with Acidocerus Klug , Chasmogenus Sharp , Dieroxenus Spangler , Globulosis García, Helochares Mulsant , Helobata Bergroth , Helopeltarium Orchymont , Horelophopsis Hansen , Peltochares Régimbart , Quadriops Hansen , Tobochares Short & García , and Troglochares Spangler. It can be characterized and differentiated from the genera mentioned above by the following characters:

Body length 1.4̄ 4.8 mm (in contrast to Peltochares with 9–11 mm body length, and some large species of Helochares and Helobata ). Habitus slender to broad (E.I.=1.0̄1.6); mostly oval shaped or with parallel-sided elytra, few species with elytra widening posterior to midlength (shared with Acidocerus , Horelophopsis and many species of Helochares ); generally weakly to moderately convex dorsally, rarely strongly convex (strongly convex in Globulosis ); elytra not explanate laterally (in contrast to Acidocerus , Helobata , Helopeltarium , Peltochares , and Quadriops ). Outline of body not inerrupted between pronotum and elytra (in contrast to Horelophopsis ).

Head. Labrum not concealed by anteriorly enlarged clypeus (in contrast to Helobata and Helopeltarium ), anterior margin of clypeus slightly to distinctly emarginate (emargination absent in Helobata and Quadriops ); compound eyes present (in contrast to Troglochares ), not subdivided (in contrast to Quadriops ), not excised anteriorly (in contrast to Dieroxenus , Helobata , Helopeltarium and some species of Helochares ). Antennae with eight or nine antennomeres. Mentum without ventral ridge (in contrast to Helobata ), with anterior impression (shared with all Acidocerinae ). Maxillary palpi 0.7̄1.5 × as long as width of head anterior to eyes (shared with most genera of Acidocerinae , shorter in Horelophopsis and Quadriops ; longer in Peltochares ); palpomeres straight, not curving mesad, palpomere 2 club-shaped (in contrast to all other genera of Acidocerinae with either mesad bending palpomere 2, 3 or 4, or ( Horelophopsis ) with swollen palpomere 2. Ground punctation and systematic punctures present.

Thorax. Pronotum with ground punctation and systematic punctures (shared with most genera of Acidocerinae ), punctation not granulate (in contrast to Acidocerus ). Prosternum not carinate (in contrast to Acidocerus ), procoxal cavities open posteriorly (in contrast to Helobata ). Mesoventrite simply bulged or with low transverse ridge; rarely with low carina (shared with Dieroxenus and Horelophopsis ; strong carina present in Chasmogenus ). Metaventrite without projection (carinate in Helobata ). Elytra with irregular series of very course punctures in few species, without regular serial punctures or striae (ten rows of regular serial punctures or punctate striae present in Acidocerus , Horelophopsis , Peltochares , Quadriops , Tobochares , and in some subgenera of Helochares ); scutellary stria absent (present in Horelophopsis , Peltochares , and in some Helochares ), pubescence on mesofemur present (shared with all Acidocerinae ), on metafemur present or absent (absent only in Quadriops ). Tarsi five-segmented (shared with all Acidocerinae ).

Abdomen. Apical emargination of abdominal ventrite 5 present or absent (absent in Globulosis , Horelophopsis , Quadriops , Tobochares , Troglochares , and some Helochares ).