Helopeltarium d'Orchymont , 1943

Giron, Jennifer C. & Short, Andrew Edward Z., 2021, The Acidocerinae (Coleoptera, Hydrophilidae): taxonomy, classification, and catalog of species, ZooKeys 1045, pp. 1-236 : 1

Genus Helopeltarium d'Orchymont, 1943 Figs 1H , 2 , 5 , 37I , 38

Helopeltarium d’Orchymont, 1943f: 9.

Gender.

Masculine.

Type species.

Helopeltarium ferrugineum d’Orchymont, 1943f: 10; by original designation and monotypy.

Diagnosis.

Small beetles, body length nearly 3.5 mm. Body broadly oval and explanate in dorsal view, rather flat in lateral view, with dorsal outline nearly straight along median region (Fig. 38 ). Surface smooth (without granulations or reticulations), with ground punctation strongly marked. Body orange brown, slightly paler along margins (Fig. 38 ). Shape of head somewhat trapezoid. Anterior corners of frons extended laterally and posteriorly, emarginating anterior margin of eyes. Eyes relatively small, with anterior margin markedly emarginate in lateral view, in dorsal view not projecting from outline of head. Clypeus laterally expanded in front of eyes; anterior margin of clypeus slightly emarginate. Labrum concealed under clypeus. Mentum with surface obliquely striate (Fig. 38C ). Antennae with nine antennomeres, cupule strongly asymmetric, with rounded outline. Maxillary palps short and moderately stout, hardly 3/4 as long as width of head; maxillary palpomere 4 nearly as long as palpomere 3; inner margin of maxillary palpomere 2 nearly straight, outer margin curved along apical half (Fig. 38C ). Elytra without sutural striae, broadly explanate laterally, serial punctures absent, ground punctures sharply marked, densely and uniformly distributed (Fig. 38A ). Prosternum slightly convex, not carinate medially (Fig. 38C ). Posterior elevation of mesoventrite only bulging (Fig. 38C ); anapleural sutures only slightly concave, separated at anterior margin by distance similar to anterior margin of mesepisternum. Metaventrite uniformly covered by hydrofuge pubescence (Fig. 38C ). Protibiae with spines of anterior row long, thick, and semi-erect; apical spurs of protibiae stout, extending to apex of protarsomere 2. Metafemora without distinct tibial grooves; hydrofuge pubescence covering basal 3/4 of anterior surface of metafemora (Fig. 38C ). Tarsomeres 2-4 ventrally densely covered by setae; metatarsomere 1 much shorter than 2; metatarsomere 5 nearly as long as metatarsomere 2 or 3 and 4 combined. Fifth abdominal ventrite apically emarginate, with fringe of flat and stout setae. Aedeagus tubular (Fig. 37I ); distal region of each paramere diverging; apex of parameres rounded; basal piece nearly half as long as parameres; median lobe broad, apically tapering to rounded tip; gonopore not clearly visible.

Differential diagnosis.

Helopeltarium has a very unique appearance within acidocerines. The flattened and broadly explanate body shape and concealed labrum, accompanied by smooth surface, short and stout maxillary palps, lacking elytral serial punctures is unique in the subfamily. It may appear like a very small Helobata , but besides geographic origin, the lack of serial punctures, smooth surface and short maxillary palps sets Helopeltarium apart very easily. The configuration of the aedeagus in Helopeltarium , is very similar to that of some Helochares , but the external morphology alone allows for its immediate recognition.

Distribution.

Indo-Malayan: Myanmar (formerly Burma); Fig. 5 .

Natural history.

There is no natural history information available for the genus.

Larvae.

Immature stages are not known for Helopeltarium .

Taxonomic history.

Originally described by d’Orchymont (1943f: 9). Redescribed by Hansen (1991: 149).

Remarks.

In the original description, d’Orchymont (1943f) compared Helopeltarium with Helobata . As far as we know, the genus is only known from two syntype specimens of the only known species. This genus was not included in the molecular phylogeny by Short et al. (2021). Its assignment to the Helochares group is primarily based on the form of the aedeagus, as well as its distribution in the Old World. Indeed, the genitalia is very similar to those found in some clades of Helochares , and it would not be surprising to us if Helopelatarium is eventually found to be sister to or nested within Helochares .

Species examined.

Syntypes of Helopeltarium ferrugineum d’Orchymont.

Selected references.

d’Orchymont 1943f: 9: original description; Hansen 1991: 149: redescription; Short et al. 2021: phylogenetic position and affinities discussed.

Figures

Figure 1. Variation across Acidocerinae, dorsal and lateral views A Colossochares ellipticus B Peltochares sp. C Peltochares conspicuus D Aulonochares tubulus E Helochares sp. F Helochares tristis G Novochares sp. H Helopeltarium ferrugineum I Batochares sp. J Helobata larvalis K Radicitus sp. L Nanosaphes tricolor M Agraphydrus cf. attenuatus N Tobochares luteomargo O Tobochares sulcatus P Quadriops similaris Q Crucisternum ouboteri R Primocerus neutrum S Agraphydrus coomani T Agraphydrus sp. U Globulosis flavus V Crephelochares nitescens.

Figure 2. Phylogeny of the Acidocerinae simplified from Short et al. (2021), indicating the distribution, preferred habitat, and currently described number of species for each genus. For habitat, filled black circles indicate that at least some species of the genus are commonly found in this habitat; light grey circles indicate the genus has been found in this habitat, but is rare or not typical for the group; white circles indicate no species have been recorded for the genus in this habitat.

Figure 5. Known distribution of genera of Acidocerinae: Crucisternum, Ephydrolithus, Globulosis, Helobata, Helochares, Helopeltarium, Katasophistes, and Nanosaphes.

Figure 37. Aedeagi A-H Helochares spp.: A H. sp. (Guinea) B H. tristis C H. nr. cresphontes D H. nr. tatei E H. sp. (India, Goa) F H. sp. (Vietnam) G H. politus H H. songi (from Jia and Tang 2018, fig. 48) I Helopeltarium ferrugineum. Scale bars: 0.5 mm.

Figure 38. Habitus of Helopeltarium ferrugineum A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.