Acidocerus Klug, 1855: 649.

Body length 1.2–14.0 mm. Body shape oval in dorsal view, dorsoventrally flattened, or weakly to strongly convex in lateral view (Fig. 1); surface even (without elevations or depressions), granulate (e.g., Figs 17, 33) or smooth on head and pronotum. From yellowish to dark brown in coloration (Fig. 1), usually uniform, sometimes different regions of body colored differently. Shape of head variable (trapezoid, subquadrate, round; Fig. 11E–L). Anterior corners of frons sometimes extended posteriorly forming canthus and emarginating anterior margin of eyes (e.g., Tobochares, Helobata; e.g., Fig. 11B, C). Eyes varying in size, shape, degree of emargination, and degree of projection from outline of head (Fig. 11E–L); absent only in cavernicolous genus Troglochares Spangler, 1981a. Clypeus variable in shape (rectangular to trapezoid; Fig. 11E–L), with anterior margin from straight to mesally emarginate. Labrum usually exposed; concealed by clypeus in Helobata (Fig. 11L) and Helopeltarium (Fig. 1H). Mentum usually wider than long, with strong median anterior depression, may be limited by low transverse carina (Fig. 12A–C); surface of mentum with variable sculpture, ranging from smooth (Fig. 12A) to roughly punctate or obliquely striate (Fig. 12B). Antennae with eight or nine antennomeres (Fig. 12D, E), with cupule varying in symmetry and shape. Maxillary palps curved inward, ranging from very short (nearly half width of the head; e.g., Quadriops reticulatus, Fig. 12C) and stout, to very long and slender (nearly twice the width of the head; e.g., Peltochares, Fig. 11K). Pronotum evenly convex, usually with systematic punctures forming paired anterolateral semicircles and paired short posterolateral transverse bands. Elytra with or without sutural striae, with outer margins simple, slightly flared, or laterally explanate; elytral punctation variable (Fig. 13). Hind wings usually well developed (Fig. 15A–F), seldom reduced along apical region (Fig. 15G). Surface of prosternum flat (e.g., Fig. 14A, B), convex or rarely medially carinate (e.g., Crucisternum; Fig. 29C), with anterior margin straight or anteriorly projected. Posterior elevation of mesoventrite either only weakly bulging or with transverse (e.g., Fig. 14E, G) or longitudinal ridge (e.g., Fig. 14D, F); with strongly produced, anteriorly pointed and longitudinally carinate transverse ridge in Crucisternum (Fig. 14C). Anapleural sutures variable in shape and orientation. Metaventrite rather uniformly covered by hydrofuge pubescence (e.g., Fig. 14E), sometimes with posteromesal glabrous patch (e.g., Fig. 14D, F, G), sometimes also with posterolateral glabrous patches (e.g., Fig. 14D). Protibiae with anterior row of spines varying in shape and development; apical spurs of protibiae varying in development. Metafemora with tibial grooves of varying development; hydrofuge pubescence on anterior surface of metafemora absent, reduced to only basal or dorsal patch, or increasingly covering most of surface. Tarsomeres 5-5-5; tarsomeres variable in size, proportions, and dorsal and ventral coverage. Abdomen with five pubescent ventrites, density of setae ranging from sparse to very dense. Fifth abdominal ventrite with apex either rounded (Fig. 15I), truncate (Fig. 15J), or emarginate (Fig. 15H); apex with or without fringe of flat and stout setae. Aedeagus usually symmetrical (Fig. 16), with basal piece varying in size from longer than parameres (e.g., Primocerus, Fig. 47; Batochares, Fig. 22D), to reduced and virtually absent (e.g., Peltochares, Fig. 45); parameres highly variable in shape, either slender and only connected to each other at base of ventral surface (e.g., Fig. 16A–D, G, H), or fused together forming tube-like structure (e.g., Fig. 16E, F); apex of parameres either simple, or bifurcated and modified with hooks and spines (e.g., Fig. 16C, D); median lobe either simple or with dorsal and ventral lobes, with well-developed lateral basal apodemes; further modifications (longitudinal divisions, presence of internal hooks and spines, development of gonopore) widespread.

Acidocerines can be generally recognized by their oval and moderately convex body shapes with slender maxillary palps and uniformly slender tibiae (usually strongly convex and sometimes rounded in Cylominae and Sphaeridiinae, with short and stout maxillary palps and stout to apically broadened tibiae). The maxillary palps are always curved inwards in Acidocerinae (maxillary palpomere 2 with inner margin straight to concave; Fig. 12F–J), with palpomeres 2–4 similar in length and proportions (curved outwards, zig-zag oriented, or with shorter palpomere 3 in most Enochrinae and Chaetarthriinae). In addition, Acidocerines always bear five tarsomeres on the meso- and metatarsi (four in some enochrines).

Hansen 1991: diagnosis of the group (at the time as a subtribe, and including some genera now placed in the subfamily Enochrinae), list of genera and subgenera with synonyms, key to genera, and description of each genus (8 out of the 23 recognized in this paper). Hansen 1999b: catalog with full list of species at the time (nearly 300), synonyms and references. Short and Fikáček 2013: Acidocerinae as a subfamily excluding enochrine genera, with Horelophopsinae as synonym, list of genera, general diagnosis. Short et al. (2021): molecular phylogeny and biogeography of the subfamily, groups of genera.

The subfamily Acidocerinae is a group with many contrasts. It includes some of the largest as well as smallest hydrophilids; some genera are either strikingly different from, or extremely similar to others; the external morphology of some genera is extremely uniform and species can only be recognized by characters of the male genitalia, or so variable that is difficult to diagnose the group as a unit; at the species level, the distributions can be very narrow and restricted to one or a few fairly close localities, or very broadly widespread across several continents. There is a trend for species living in the same kind of habitats to have certain shared morphological features. For example, species that live in aquatic habitats tend to have slender and relatively long maxillary palps and metafemora mostly covered by hydrofuge pubescence, whereas species living in hygropetric habitats tend to have shorter and stouter maxillary palps and reduced or absent coverage of hydrofuge pubescence on the metafemora.

Masculine.

Acidocerus aphodioides Klug, 1855: 649; by monotypy.

Small beetles, body length nearly 2.8 mm. Body shape elongate oval in dorsal view, moderately convex in lateral view, with dorsal outline nearly straight along anterior 2/3 of elytra (Fig. 17). Surface of head and pronotum granulate (Fig. 17C). Body pale/yellowish brown, with head slightly darker. Eyes with anterior margin straight in lateral view (not emarginate), in dorsal view slightly projecting from outline of head (Fig. 17C). Labrum not concealed by clypeus (Fig. 17C). Antennae with nine antennomeres, with strongly asymmetric cupule, with longer side acute. Maxillary palps elongate, with palpomere 4 nearly as long as palpomere 3 (d’Orchymont 1943f: 7, in key). Elytra without sutural striae, narrowly explanate laterally, serial punctures strongly marked, arranged in rows (Fig. 17A). Prosternum flat, rather sharply carinate medially, with angulate anteromedian projection. Posterior elevation of mesoventrite only weakly bulging. Metaventrite with hydrofuge pubescence. Metafemora without distinct tibial grooves, mostly pubescent, only glabrous at apex. Metatarsomeres 1–4 similar in length; metatarsomere 5 similar in length to metatarsomeres 1–4 combined. Fifth abdominal ventrite apically emarginate, with stout setae.

Figure 17. 

Habitus of Acidocerus aphodioides A dorsal habitus B lateral habitus C head. Scale bar: 1 mm.

The long fifth metatarsomere (longer than metatarsomeres 1–4 combined) is unusual but not unique in the subfamily (Hansen 1991). The granulate surface of the head and body resembles that of Helobata, but besides their geographic origin, the exposed labrum of Acidocerus (as opposed to concealed in Helobata) allows its recognition. The small size and coarse punctation of the elytra of Acidocerus resemble some of the Old World Helochares (e.g., Fig. 36D–F) and some Agraphydrus (e.g., Agraphydrus hanseni, Fig. 19A), from which it can be differentiated by the medially sharply carinate prosternum (Hansen 1991).

Afrotropical: Mozambique; Fig. 4.

There is no natural history information available for the genus.

Immature stages are not known for the genus.

The taxon was originally described as related to Spercheus Kugelann, with maxillary palps similar to those of Hydraena Kugelann (Klug 1855), and even later afforded its own subfamily (see taxonomic history of the Acidocerinae section, above). d’Orchymont (1943f: 7) provided a list of diagnostic characters in a key, including the relative length of its tarsal segments, specifically that the fifth tarsomere is as long as tarsomeres 1–4 combined. Hansen (1991) redescribed the taxon based on syntypes. Hansen (1991: 149) further commented that he had seen other “typical” species of Helochares that also shared this feature and stated that “although Acidocerus may be somewhat reminiscent of a small Helochares… I prefer to maintain it as a distinct genus at the present stage”. The genus was not included in the molecular phylogeny in Short et al. (2021), and its assignment to the Helochares group is based primarily on its overall dorsal sculpturing, lack of a sutural stria, and Afrotropical distribution.

Only one described species. Hansen (1991) studied Klug’s syntypes housed at the Museum für Naturkunde der Humboldt-Universität in Berlin, Germany (ZMHB), which are the only known specimens for the genus. The diagnostic features listed above include information from d’Orchymont (1943f), Hansen (1991), and our own observations of photographs of the syntypes. Given that the specimens were mounted on cards when photographed, features of the ventral surface were not viewed by us. Characters of the ventral features (as well as the maxillary palps) as described above are based on d’Orchymont (1943f) and Hansen (1991), as the maxillary palps appeared to be missing by the time Hansen examined the syntypes. Until additional specimens are found, it is unlikely there will be a satisfactory resolution on deciding if Acidocerus is in fact a distinct genus or rather another variant of Helochares.

Acidocerus aphodioides (photographs of syntypes).

Klug 1855: 649: original description; d’Orchymont 1943f: 7: offers diagnostic features in a key; Hansen 1991: 149: redescription; Short and Fikáček 2013: 741: Acidocerus listed in subfamily Acidocerinae; Short et al. 2021: phylogenetic position and affinities discussed.

Masculine.

Agraphydrus punctatellus Régimbart, 1903: 34; by monotypy.

Small beetles, body length 1.4–4.8 mm. Body shape elongate to broadly oval in dorsal view, weakly to moderately convex in lateral view, rarely strongly convex (Figs 18, 19). Surface of head and pronotum smooth, usually with shallow ground punctation. Body ranging from pale/yellowish to dark brown (Figs 18, 19), either uniform across body regions or with different regions colored differently (e.g., darker head, paler elytra and margins of pronotum; Fig. 18A, B). Eyes with anterior margin straight in lateral view (not emarginate), in dorsal view slightly projecting from outline of head. Clypeus moderately convex, with distinct systematic punctures, with anterior margin slightly to clearly emarginate. Labrum not concealed by clypeus. Mentum nearly 1.5 × wider than long, with variable surface, with wide and moderate median anterior depression limited by low transverse carina. Antennae with eight or nine antennomeres, with slightly asymmetric cupule, round in outline. Maxillary palps elongate, 0.7–1.5 × width of head, with inner margin of palpomere 2 usually straight and palpomere 4 nearly as long to slightly longer than palpomere 3 (Fig. 12G). Pronotum with ground punctation usually moderate. Elytra without sutural striae, not laterally explanate, with serial punctures usually absent; systematic punctures usually rather sparse and aligned in four rows along elytra. Prosternum slightly convex, not carinate medially. Posterior elevation of mesoventrite variable, from simply bulged, to bearing variously shaped elevations; anapleural sutures variable in shape and orientation. Metaventrite with posteromedian glabrous patch. Metafemora without distinct tibial grooves, either mostly pubescent (only glabrous at apex), or with pubescence reduced to small basal area (“Gymnhelochares”). Metatarsomere 1 shorter than 2; metatarsomere 2 slightly shorter than 5; metatarsomere 5 similar in length to metatarsomeres 3 and 4 combined. Fifth abdominal ventrite apically emarginate, sometimes very slightly, or rounded, with or without fringe of stout setae. Aedeagus trilobed in form (Fig. 20); basal piece shorter to longer than parameres; outline of apical region of parameres variable; median lobe triangular, with well-developed lateral basal apodemes, usually rounded at apex; gonopore well developed.

Figure 18. 

Habitus of Agraphydrus spp. A–C A. coomani: A dorsal habitus B lateral habitus C ventral habitus D–F A. cf. attenuatus: D dorsal habitus E lateral habitus F ventral habitus G–I A. sp. ex Madagascar: G dorsal habitus H lateral habitus I ventral habitus. Scale bars: 1 mm.

Figure 19. 

Habitus of Agraphydrus spp. A A. hanseni B A. jilanzhui C A. longipalpus D A. contractus E A. anhuianus F A. puzhelongi. Images B–F from Komarek and Hebauer (2018). Scale bars: 1 mm.

Figure 20. 

Aedeagi of Agraphydrus spp. A A. attenuatus B A. gracilipalpis C A. masatakai D A. chinensis E A. puzhelongi. Scale bars: 0.1 mm. Line drawings taken from Komarek (2018).

Agraphydrus can be considered highly variable both morphologically and ecologically. Given their usually small to very small size, in the regions where Agraphydrus is distributed, they may be confused with smaller species of Helochares, from which Agraphydrus can be distinguished by the presence of a posteromesal glabrous patch on the metaventrite (metaventrite uniformly and densely covered by hydrofuge pubescence in Helochares); their size allows to differentiate them from the much larger Colossochares and Peltochares. The lack of sutural stria in Agraphydrus allows to recognize the larger Agraphydrus from similarly sized Crephelochares. The maxillary palps tend to be shorter in Agraphydrus. Most Agraphydrus have moderately punctate head and pronotum and generally lack elytral serial punctures; although they may have very coarse systematic punctures somewhat aligned in rows, these rows are not quite uniform as in many Old World Helochares or Acidocerus. The outer margins of the elytra of Agraphydrus are only slightly flared, as opposed to laterally expanded which differentiates them from Batochares. The most similar genus to Agraphydrus would be the Neotropical genus Tobochares, but they do not co-occur; the body shape in Agraphydrus, in general, tends to be more elongated (1.1–1.4 × longer than wide), whereas in Tobochares it tends to be only slightly longer than wide (1.07–1.15 × longer than wide); in addition, the metafemora in Tobochares are always mostly glabrous, with scattered setae, and their serial punctures are well aligned longitudinally.

Afrotropical: Angola, Botswana, Cameroon, Democratic Republic of the Congo, Djibouti, Eritrea, Eswatini, Ethiopia (in doubt), Gabon, Ghana, Guinea, Ivory Coast, Kenya, Madagascar, Malawi, Mozambique, Namibia, Nigeria, Oman, Republic of South Africa, Saudi Arabia, Sudan, Tanzania, United Arab Emirates, Yemen, Zimbabwe. Australasian: Australia (New South Wales, Northern Territory, Queensland, Western Australia), Indonesia (Java, Papua), Papua New Guinea. Indo-Malayan: Bhutan, Brunei, China (Fujian, Guangdong, Guangxi, Guizhou, Hainan, Himachal, Hong Kong, Hunan, Jiangxi, Taiwan, Yunnan, Zhejiang), India (Arunachal Pradesh, Assam, Goa, Himachal Pradesh, Kerala, Karnataka, Madhya Pradesh, Maharashtra, Meghalaya, North Andaman Island, Sikkim, Tamil Nadu, Uttar Pradesh, Uttarakhand), Laos, Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand, Vietnam. Palearctic: China (Anhui, Gansu, Hubei, Shaanxi, Shandong, Sichuan, Tibet), Iran, Japan, Korea, Pakistan, South Korea; Fig. 4.

Agraphydrus can be found in an extremely broad range of habitats, from rivers, streams and forest pools, to hygropetric environments around waterfalls or seepages over rocks; a few species have been collected in terrestrial habitats by sifting moss and leaves from near water bodies, or in the gravel along the bank of a river; in many cases specimens have been found associated with floating vegetation, mosses and algae (Komarek 2018, 2019, 2020, Komarek and Freitag 2020, Komarek and Hebauer 2018).

Only the larvae of two species of Agraphydrus are currently known: A. narusei (Satô) (first and third instars; Minoshima and Hayashi 2011), and A. hanseni (Satô and Yoshitomi) (third instar; Minoshima et al. 2013). Minoshima (2016) offers a diagnosis for Agraphydrus larvae.

Originally described as a genus by Régimbart in 1903; downgraded to a subgenus of Enochrus by d’Orchymont (1919c: 155); transferred as a subgenus to Helochares by d’Orchymont (1927a: 250); generic status re-established by Satô (1965: 128). Hansen (1991: 148) placed Gymnhelochares as a subgenus of Agraphydrus; Komarek and Hebauer (2018: 17) placed Gymnhelochares as a synonym of Agraphydrus given that they could not identify any unique morphological traits that allowed the two genera to be differentiated. Minoshima et al. (2015: 7) synonymized Megagraphydrus with Agraphydrus also based on the lack of morphological traits in support of their separation. Short and Fikáček (2013) recovered Horelophopsis and Agraphydrus as sister taxa within the Acidocerinae (Horelophopsis had been described as, and was prior to Short and Fikáček (2013), its own subfamily of Hydrophilidae). These affinities between Agraphydrus and Horelophopsis were also recognized by Minoshima et al. (2013) based on larval characters. Finally, Short et al. (2021), based on their molecular phylogenetic analyses, synonymized Horelophopsis with Agraphydrus, as Horelophopsis was recovered as a lineage nested within Agraphydrus. The genus was redescribed by Komarek (2020). For more details on the taxonomic history of the genus and its synonyms see Minoshima et al. (2015).

With 201 described species, Agraphydrus is currently the largest genus of Acidocerinae, due to a series of recent revisions and monographs (Minoshima et al. 2015; Komarek 2018, 2019, 2020; Komarek and Hebauer 2018; Komarek and Freitag 2020), making it the fifth largest genus of Hydrophilidae (behind Berosus Leach, Laccobius Erichson, Cercyon Leach, and Enochrus Thomson). The condition of the maxillary palpomere 2 being straight (with inner margin straight) is not unique to Agraphydrus but shared with Tobochares and some Helochares. Minoshima et al. (2015) proposed the V-shaped male abdominal sternite 9 as a possible synapomorphy of the genus, but the condition is shared with some members of the Tobochares group.

The genus appears well supported as monophyletic as currently defined, despite its substantial morphological and ecological variation (Short et al. 2021). Although previous decisions to synonymize derived genera (e.g., Megagraphydrus, Pseudopelthydrus, Horelophopsis) were necessary to preserve the monophyly of the broader concept of Agraphydrus, it has rendered the genus unmanageably large and with no internal formal or informal classification system. The lineage would be well-served by further phylogenetic studies to define species groups or to partition into subgenera.

Hebauer (2002a) listed several species of Agraphydrus as “in press”, and some specimens in collections bear associated red and orange holotype or paratype labels bearing these names; however, those were never formally published. Many of these taxa appeared in Komarek and Hebauer (2018) or subsequent revisions by Komarek (2019, 2020), with names different from those proposed by Hebauer (2002a).

Agraphydrus anatinus Komarek, A. attenuatus (Hansen), A. coomani (d’Orchymont), A. decipiens Minoshima, Komarek & Ôhara*, A. hanseni (Satô & Yoshitomi), A. insidiator Minoshima, Komarek & Ôhara*, A. ishiharai (Matsui), A. kempi (d’Orchymont), A. luteilateralis (Minoshima & Fujiwara)*, A. malayanus (Hebauer)*, A. masatakai Minoshima, Komarek & Ôhara*, A. minutissimus (Kuwert), A. narusei (Satô), A. pauculus (Knisch), A. politus (Hansen), A. pygmaeus (Knisch), A. siamensis (Hansen), A. stagnalis (d’Orchymont), A. thaiensis Minoshima, Komarek & Ôhara, and numerous unidentified specimens. For species marked with an asterisk, paratype specimens were studied.

Minoshima et al. 2015: character discussion, taxonomic history, synonymization of Megagraphydrus, description of seven new species; Komarek and Hebauer 2018: 17: synonymized the subgenus Gymnhelochares with Agraphydrus, taxonomic revision for China and Taiwan describing 33 new species; Komarek 2018: taxonomic revision for India describing 36 new species; Komarek 2019: taxonomic revision for South East Asia (except Philippines) and Australasian Region, describing 60 new species; Komarek and Freitag 2020: revision of the species from the Philippines describing nine new species and providing barcodes for the species treated therein; Komarek 2020: revision of the African and Western Asian species, describing 25 new species and redescribing the genus; Short et al. 2021: synonymization of Horelophopsis with Agraphydrus, phylogenetic placement of Agraphydrus.

Masculine.

Aulonochares tubulus Girón & Short, 2019: 120; by original designation.

Medium sized beetles, total body length 5.8–7.5 mm. Body shape elongated oval in dorsal view; weakly convex in lateral view (Fig. 21). Color orange brown to dark brown; ventral surface covered with rather long golden setae, especially on abdominal ventrites, and more densely so (with shorter setae) on surface of femora. Head subquadrate in dorsal view, seemingly constricted at anterior margin of eyes (Fig. 11J). Eyes relatively small, separated by distance nearly 6.5 × the maximum width of an eye (Fig. 11J). Clypeus with lateral margins nearly parallel, slightly convex, with anterior margin only slightly narrower than posterior margin (Fig. 11J). Labrum fully exposed. Mentum and submentum roughly punctate (Fig. 21C). Antennae with nine antennomeres, with cupule slightly asymmetrical and round in outline. Maxillary palps long, nearly 1.5 × longer than maximum width of head, with inner and outer margins of maxillary palpomere 2 evenly curved (Fig. 21A). Pronotum with ground punctation shallow and uniformly sparse. Elytra without sutural striae, with outer margins slightly flared; serial punctures, ground punctures and systematic punctures similar in size, shallowly impressed. Surface of prosternum flat (slightly carinate only along midline of antero-mesal projection of anterior margin). Posterior elevation of mesoventrite simple, without carinae or ridges; anapleural sutures concave, anteriorly converging, anteriorly separated by distance nearly 0.3 × as wide as anterior margin of mesepisternum. Metaventrite densely and uniformly pubescent. Protibiae with spines of anterior row very small and appressed (Fig. 21C); apical spurs of protibiae very short (not exceeding the length of the first tarsomere) and stout. Hydrofuge pubescence covering most surface of metafemora (Fig. 21C). Ventral face of tarsomeres 1–4 densely covered by stiff setae. Apex of fifth abdominal ventrite strongly emarginate; emargination fringed by stout setae. Aedeagus tubular (Fig. 22A–C), somewhat cylindrical, with parameres forming a 5–7 × longer than wide tube; basal piece very short and strongly concave; gonopore reduced, located at apex of median lobe.

Figure 21. 

Habitus of Aulonochares spp. A–C A. tubulus: A dorsal habitus B lateral habitus C ventral habitus D A. lingulatus, dorsal habitus. Scale bar: 5 mm.

Figure 22. 

Aedeagi of Aulonochares and Batochares spp. A A. tubulus B A. novoairensis C A. lingulatus D B. sp. Scale bars: 0.5 mm.

Aulonochares can be easily mistaken with Novochares in the New World, and the two genera can be collected together. The subquadrate shape of the head (Fig. 11J; as opposed to trapezoid as in Fig. 11G), the roughly punctate mentum, the long setae composing the ventral pubescence of the abdominal ventrites, ventrally densely setose tarsomeres, along with the tubular shape of the aedeagus (Fig. 22A–C) are very distinctive and uniquely combined in Aulonochares among Neotropical acidocerines.

Neotropical: Brazil (Amazonas, Roraima), French Guiana, Guyana, Suriname, Venezuela; Fig. 4.

Specimens of Aulonochares have been collected in densely forested sandy streams and detrital pools in forests along creeks. They seem to prefer habitats with abundant detritus or decaying organic matter. Females of A. tubulus and A. ligulatus have been observed carrying their egg cases underneath their abdomen (Girón and Short 2019; pers. obs.).

Immature stages are not known for the genus.

Recently described by Girón and Short (2019).

Only three species are known for the genus (Girón and Short 2019).

Aulonochares lingulatus Girón & Short, A. novoairensis Girón & Short, A. tubulus Girón & Short. Holotypes and paratypes of all three species were available for this study. We have not seen any specimens of the genus from outside the Guiana Shield region of South America.

Girón and Short 2019: original description of the genus and all its currently known species; Short et al. 2021: phylogenetic placement.

Masculine.

Helochares (Batochares) burgeoni d’Orchymont, 1939b: 294; by original designation (Hansen 1991: 292).

Body length between 3–4 mm. Body shape oval in dorsal view, moderately convex in lateral view, with dorsal outline nearly straight along basal 2/3 (Fig. 23). Dorsal surfaces smooth, uniformly covered by short setae, brown to pale brown in coloration, either uniform or with yellowish patches along margins of pronotum and elytra, or scattered throughout surface giving spotted appearance (Fig. 23A, B); ground punctation fine and shallow; ventral surfaces rather densely covered by rather long and fine golden setae. Head rather oval in dorsal view, clearly constricted at anterior margin of eyes (Fig. 11E). Eyes not emarginate, moderate in size, separated by nearly 3.8 × width of eye, strongly projected from outline of head (Fig. 11E). Clypeus with anterior margin broadly emarginate, with medial region of emargination nearly straight; anterior corners round. Labrum fully exposed, with apical region anteriorly flattened, thus forming fine transverse carina across anterior region (Fig. 11D). Mentum rather flat, surface laterally punctate, mesally and anteriorly striate, with anteromedial region depressed. Submentum finely and shallowly punctate. Antennae with nine antennomeres, with strongly asymmetric and round cupule. Maxillary palps nearly 1.5 × longer than maximum width of head, with palpomere 4 0.8 × as long as palpomere 3 (Fig. 23C); inner margin of maxillary palpomere 2 nearly straight, outer margin apically slightly curved. Pronotum medially evenly convex, explanate and somewhat bending upwards along antero-lateral areas; posterior margin of pronotum clearly narrower than anterior margin of elytra combined. Elytra without sutural striae, with outer margins explanate, especially along anterior third; serial punctures well developed, forming longitudinal rows, at least well defined along outer areas, or visible along entire length of elytra; seta bearing systematic punctures irregularly distributed. Surface of prosternum slightly elevated along midline, with anterior margin acutely triangular and slightly projected anteriorly. Posterior elevation of mesoventrite rather flat; intercoxal process of mesoventrite broad (nearly as wide as antennal club), apically truncate; anapleural sutures sinuate, separated at anterior margin by distance slightly shorter than anterior margin of mesepisternum. Metaventrite with medial surface elevated as platform, densely covered with hydrofuge pubescence, except for posterolateral patches (Fig. 23C). Protibiae with spines of anterior row very fine and erect; apical spurs of protibiae small (larger spur similar in size and shape to tarsal claws). Metafemora without tibial grooves; metafemora with hydrofuge pubescence covering at least basal 2/3 of anterior surface (Fig. 23C). Metatarsomere 5 1.5 × longer than metatarsomere 2, metatarsomere 2 nearly as long as metatarsomeres 3 and 4 combined; tarsomeres 1 to 4 with sparse long setae on dorsal surface, and spiniform dense setae on ventral surface; tarsomere 5 with few setae along apical margin. Abdomen with five pubescent ventrites. Fifth abdominal ventrite with apex broadly truncate, without stout setae. Aedeagus trilobed, with basal piece nearly as long as parameres (Fig. 22D); parameres somewhat triangular, slender and apically narrowing; median lobe tapering to round apex; gonopore well-developed.

Figure 23. 

Habitus of Batochares sp. A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.

Batochares differs from all other known acidocerines by its unique labrum (with apical region anteriorly flattened, forming a transverse carina across anterior region; Fig. 11D), combined with oval head which is constricted at the anterior margins of the eyes, anterolaterally explanate pronotum, explanate elytra, rows of serial punctures visible at least along outer margins, broadly truncate posterior margin of fifth abdominal ventrite, and unusually large basal piece of the aedeagus (longer than parameres). These features, especially the configuration of the labrum, pronotum and elytra, along with the yellow spots along the surface of the elytra distinguish Batochares from all other known acidocerines.

Afrotropical: Burundi/Rwanda, Central African Republic, Democratic Republic of the Congo, Gabon, Guinea, Kenya, Republic of the Congo, Uganda; Fig. 4.

Little natural history information is available for the genus. Recent collecting data for a few series suggests it may be associated with the margins of streams and small rivers.

Immature stages for Batochares remain unknown.

Batochares was described as a subgenus of Helochares by d’Orchymont (1939b) who did not explicitly designate a type species; therefore, the subgenus name was unavailable according to article 13.3 of the ICZN (1999). In 1991, Hansen validated Batochares as a subgenus of Helochares by fixing the type species for it; therefore, under article 50.1 of the Code (ICZN 1999), Hansen is granted authorship of the subgenus name. d’Orchymont considered Batochares as a subgenus of Helochares based for the most part in the number of antennomeres, relatively long maxillary palps, characters of the mentum and pubescent femora, even though the author recognized the distinctiveness of the shape of the head and the explanate elytra. Batochares was elevated to full generic status based on the phylogenetic analysis in Short et al. (2021), in which it was resolved as an early-diverging, isolated lineage within the Helochares group.

There are three species of Batochares described to date. In his description of Batochares corrugatus Balfour-Browne (1958a: 183), the author pointed out that his record of B. burgeoni from Mutsora, Parc National Albert (currently Virunga National Park, Democratic Republic of the Congo; Balfour-Browne 1950b) was not actually B. burgeoni, but a larger and likely different species. The author also indicated the existence of a different species from Angola.

Batochares burgeoni (d’Orchymont) and B. byrrhus (d’Orchymont).

d’Orchymont 1939b: 293: original description; Balfour-Browne 1958a: 183: description of one additional species; Hansen 1991: 292: type species designated, subgenus validated; Short et al. 2021: generic status, phylogenetic position and affinities discussed.

Masculine.

Chasmogenus fragilis Sharp, 1882: 73; by monotypy.

Body length ranging from 2.5–5.0 mm. Body shape oval in dorsal view, parallel-sided to broader around midlength, dorsoventrally flattened, weakly to moderately convex in lateral view (Fig. 24), either evenly convex or flattened along anterior half. Surface of head, pronotum and elytra smooth, with usually shallow ground punctation. Coloration ranging from yellowish orange to dark brown, usually uniform along body, sometimes darker on head or only frons. Shape of head trapezoid (Fig. 11H). Eyes varying in size, usually subquadrate in dorsal view, only very weakly emarginated anteriorly, and usually projected from outline of head. Clypeus trapezoid, with anterior margin mesally weakly to strongly emarginated; membranous preclypeal area visible when clypeus strongly emarginated (Fig. 11H). Labrum fully exposed, semioval, anteriorly mesally emarginated. Mentum usually rather smooth, with anterior depression often reaching midlength of mentum, sometimes limited by low transverse carina. Antennae with eight antennomeres, with cupule slightly asymmetric and rounded. Maxillary palps usually slender and slightly longer than width of head, with inner margin slightly and evenly curved, and outer margin curved along apical half. Pronotum evenly convex. Elytra with sutural striae, with outer margins slightly flared; ground punctures usually only shallowly marked, serial punctures absent and at least one median row of systematic punctures clearly visible on each elytron (Fig. 24). Surface of prosternum usually flat, only rarely with low medial carina along intercoxal process. Posterior elevation of mesoventrite with an either blunt or sharp longitudinal elevation; anapleural sutures sinuate, separated at anterior margin by distance similar or slightly shorter than anterior margin of mesepisternum. Metaventrite with posteromesal and posterolateral glabrous patches (Fig. 24C). Protibiae with spines of anterior row semi erect, relatively long, thick and sparse; apical spurs of protibiae moderately long and thick, reaching apex of protarsomere 2. Metafemora with tibial grooves moderately developed, with sharp posterior margin; hydrofuge pubescence covering at least basal 3/4 of anterior surface of metafemora (Fig. 24C, F). Metatarsomeres 2–4 with two rows of spiniform setae on ventral surface; metatarsomere 5 nearly as long as 3 and 4 combined; metatarsomere 2 shorter to nearly as long as 5. Apex of fifth abdominal ventrite emarginate, with fringe of flat and stout setae. Aedeagus trilobed (Fig. 25); basal piece shorter to nearly as long as parameres; outline of apical region of parameres variable; sometimes parameres asymmetrical; median lobe triangular, either simple or bearing additional sclerite, with well-developed lateral basal apodemes and gonopore.

Figure 24. 

Habitus of Chasmogenus spp. A–C C. ruidus: A dorsal habitus B lateral habitus C ventral habitus D–F C. cremnobates: D dorsal habitus E lateral habitus F ventral habitus G C. lineatus H C. amplius I C. itatiaia J C. fluminensis. G, H from Smith and Short 2020; I, J from Clarkson and Ferreira Jr 2014. Scale bars: 1 mm.

Figure 25. 

Aedeagi of Chasmogenus spp. A C. acuminatus B C. schmits C C. lineatus D, E C. tafelbergensis: D dorsal view E lateral view. Images from Smith and Short 2020. Scale bars: 0.5 mm.

Chasmogenus most closely resembles Crephelochares, although they do not co-occur in the same biogeographic regions (Chasmogenus occurs exclusively in the Neotropical region, whereas Crephelochares occurs throughout the Old World). They can be differentiated by the number of antennomeres (eight in Chasmogenus, nine in Crephelochares) and by the form of the aedeagus (trilobed in most Chasmogenus, Fig. 25), divided and further modified in Crephelochares, Fig. 27B–D). Among New World taxa, Chasmogenus can easily be distinguished by the presence of sutural striae, a character shared only with Primocerus, from which it can be distinguished by the shape of the posterior elevation of the mesoventrite: longitudinally elevated in Chasmogenus, transversally elevated in Primocerus. Although Primocerus is quite rare and has a more restricted range in the Neotropics compared with Chasmogenus, the two genera can co-occur in forested steams in the Guiana Shield region.

Neotropical: Argentina, Brazil (Amapá, Amazonas, Minas Gerais, Pará, Piauí, Rio de Janeiro, Roraima, São Paulo), Costa Rica, Ecuador, French Guiana, Guatemala, Guyana, Panama, Paraguay, Suriname, Venezuela; Fig. 4.

The vast majority of Chasmogenus are known from forested habitats, including the margins of streams and forest pools. A few species are known from open marsh habitats (e.g., Chasmogenus australis García and Chasmogenus sapucay Fernández). They can be found among the vegetation and submerged leaf litter. They are also attracted to lights, though usually not in large numbers. Only one species [Chasmogenus cremobates (Spangler)] has been collected in seepages. See Smith and Short (2020) for more detail on habitat information.

The larvae of Chasmogenus remain unknown. The only descriptions of immature stages were made for Chasmogenus nitescens Fauvel (from Australia), which is now assigned to Crephelochares.

Chasmogenus was originally described by Sharp (1882) as a genus to accommodate one Neotropical species from Guatemala and Panama. d’Orchymont (1919c: 149) synonymized Chasmogenus with Crephelochares (from the Old World) and placed it as a subgenus of Helochares. The generic rank of Chasmogenus was re-established by Fernández (1986: 189), with Crephelochares maintained as a junior synonym. Some authors continued to treat Crephelochares as a valid subgenus (e.g., Hebauer 1992, 1995) while others did not recognize any distinction between the two names (Hansen 1991, 1999). The monotypic genus Dieroxenus was synonymized with Chasmogenus by Girón and Short (2018). The recent phylogeny by Short et al. (2021) offered support considering Chasmogenus and Crephelochares as separate genera and affirmed Dieroxenus as a derived lineage within Chasmogenus.

There are 33 described species of Chasmogenus to date, and we are aware of many yet undescribed species in South America. Chasmogenus is a fairly commonly found group of beetles with very little variation in external morphology. Recent collecting efforts and taxonomic study in the genus have revealed a hidden diversity and interesting biogeographic patterns in South America (Smith and Short 2020).

Chasmogenus australis García*, C. amplius Smith & Short*, C. bariorum García*, C. barrae Short*, C. cremnobates (Spangler), C. lineatus Smith & Short*, C. lorenzo Short*, C. ruidus Short*, C. schmits Smith & Short*. Paratypes of the species marked with an asterisk were available for this study.

Sharp 1882: 73: genus description; Spangler 1979: 753: description of Dieroxenus; Fernández 1986: notes on the genus and one new species; Hebauer 1992: notes, recognition of two subgenera, emphasis on Crephelochares; García 2000: four new species from Venezuela; Short 2005: new species from Costa Rica; Short and Fikáček 2013: inclusion of Chasmogenus species in molecular phylogeny; Clarkson and Ferreira-Jr 2014b: four new species from Brazil; Girón and Short 2018: synonymization of Dieroxenus; Alves et al. 2020: description of a new species from Brazil; Smith and Short 2020: description of 18 new species from northeastern South America; Short et al. 2021: phylogenetic placement.

Masculine.

Helochares ellipticus d’Orchymont, 1933: 306; by present designation.

From the Latin word colossus, meaning extremely large, in reference to the comparatively large and robust bodies of the members of the genus, combined with the ending chares, expressing affinity with Helochares. Masculine.

Body length 8.5–14.0 mm. Body shape broadly oval in dorsal view, strongly and uniformly convex in lateral view (Fig. 26). Dorsal surfaces even and smooth, uniformly dark brown (nearly black) in coloration with reddish antennae, palps and tarsi; ground punctation extremely fine and shallow (Fig. 26A); ventral surfaces rather densely covered by rather long and fine golden setae (Fig. 26C). Eyes not emarginate, moderate in size, subquadrate in dorsal view, separated by nearly 4 × width of eye, projected from outline of head (Fig. 11I). Frons with large (and somewhat fused together) systematic punctures along inner margin of eye. Clypeus with anterior margin broadly roundly emarginate. Labrum fully exposed, medially convex (Fig. 11I). Antennae with nine antennomeres, with strongly asymmetric and round cupule. Maxillary palps slender, slightly longer than maximum width of head, with palpomere 4 0.7 × as long as palpomere 3 (Fig. 11I). Mentum medially broadly depressed, laterally punctate, mesally and anteriorly striate; sculpture of mentum ranging from shallow to strong. Pronotum evenly convex, and very smooth, with ground punctation very fine and shallow; systematic punctures of pronotum reduced to paired depressions near anterior margin and at midlength of lateral margins. Elytra without sutural striae, with margins slightly flared; serial punctures either absent or only visible along outer lateral area and posterior third of elytra; systematic punctures enlarged, broadly separated longitudinally, forming five rows mostly visible along outer lateral area and posterior third of elytra (Fig. 26A, B). Surface of prosternum flat to broadly convex, with anterior margin slightly projected anteriorly (Fig. 26C). Posterior elevation of mesoventrite with broad longitudinal elevation; anapleural sutures concave, anteriorly converging and separated by distance nearly 1/3 of anterior margin of mesepisternum. Metaventrite uniformly densely covered by with hydrofuge pubescence, medial surface elevated as platform. Protibiae with anterior row of spines extremely reduced to tiny and scanty, appressed denticles; apical spurs of protibiae large, outer nearly as thick and reaching apex of protarsomere 2. Metafemora with tibial grooves well-developed; metafemora with hydrofuge pubescence covering basal 4/5 of anterior surface (Fig. 26C). Metatarsomeres laterally compressed, metatarsomere 2 longer than 5, metatarsomere 5 nearly as long as 3 and 4 combined; all tarsomeres with rows spiniform setae covering ventral surface. Fifth abdominal ventrite with apex emarginate, with fringe of flat and stout setae. Aedeagus symmetrical, either trilobed (C. satoi; Hebauer 2003a: fig. 1) or highly modified (Fig. 27A), with basal piece shorter than parameres; median lobe variable.

Figure 26. 

Habitus of Colossochares ellipticus A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.

Figure 27. 

Aedeagi of Colossochares and Crephelochares spp. A Colossochares ellipticus B Crephelochares szeli C Crephelochares sp. (Australia) D Crephelochares abnormalis (Thailand). Scale bars: 0.5 mm.

Colossochares groups some of the largest acidocerines. Colossochares species are strongly and uniformly convex and highly polished, with enlarged systematic punctures on the head and elytra; systematic punctures on the pronotum are reduced to a pair of anterior and a pair of lateral depressions, not forming the usual antero-lateral semicircles that are common in acidocerines. Some members of Peltochares may exhibit similar coloration and general highly polished appearance to Colossochares (e.g., compare Fig. 1A vs. 1B); those Peltochares are always dorsoventrally flattened, generally slender, and the pronotum has systematic punctures forming antero-lateral semicircles. Other than general appearance, both genera are very similar to each other in details of the external morphology, except by the sculpture of the submentum, which is smooth in Colossochares and punctate or otherwise sculptured in Peltochares. In addition, the aedeagal form in Peltochares (spiked, Fig. 16C, D) is quite different from the forms present in Colossochares (trilobed or as in Fig. 27A).

Afrotropical: Benin, Burkina Faso, Cameroon, Democratic Republic of the Congo, Ethiopia, Gabon, Ghana, Guinea, Ivory Coast, Liberia, Malawi, Nigeria, Republic of the Congo, Uganda; Fig. 4.

Little is known about the biology of Colossochares, and no museum specimens we examined contained any habitat or collecting information. We have seen some light trap samples from Congo in which C. ellipticus is relatively common.

The larvae of species of Colossochares remain unknown.

Given how large and distinctive Colossochares species are, it is remarkable that it has not been previously recognized as a separate genus, especially given how many other genera and subgenera have been described based on less striking features. The reason may have been due in part to an original identification error: Régimbart (1907: 47) first gave a description for what is now Helochares ellipticus, but mistakenly thought they were conspecific with another already-described central African taxon, Hydrophilus ellipticus Fabricius. Régimbart (1907), based on this incorrect interpretation of his specimens, further recognized that they were not allied with Hydrophilus and instead shared similarities with Helochares, so he transferred Fabricius’ species to Helochares, creating the combination Helochares ellipticus (Fabricius). Later, d’Orchymont (1933) recognized Régimbart’s error and clarified the situation, confirming Helochares ellipticus as a valid species of Helochares, and also different from the original Hydrophilus ellipticus Fabricius.

Hebauer (2003) described Helochares satoi Hebauer and discussed its affinities with Helochares ellipticus. A specimen of Helochares ellipticus was included in the molecular phylogeny by Short et al. (2021), where it was resolved as an early-diverging and isolated member of the Helochares group of genera. Given that it is not nested within Helochares, and it is morphologically distinct, the genus Colossochares is here established to house the two species: Colossochares ellipticus (d’Orchymont) comb. nov. and Colossochares satoi (Hebauer) comb. nov.

Despite the external similarity between the two known species of Colossochares, the male genitalia are quite different from each other. This particularity is quite unusual in the subfamily given that, in general, each genus has a particular aedeagal type shared by all its species (though there are some known exceptions, e.g., Chasmogenus). The genitalia of C. satoi can be categorized as trilobed, whereas that of C. ellipticus is quite uniquely configured (Fig. 27B). More work is needed to confirm the close relationship of these two taxa.

Specimens of Colossochares ellipticus (d’Orchymont) and female paratypes of C. satoi (Hebauer) were available for study.

Régimbart 1907: 47: description of Helochares ellipticus attributed to Fabricius; d’Orchymont 1933: 306: clarification and reaffirmation of species name; Hebauer 2003: new species and discussion of affinities; Short et al. 2021: phylogenetic placement.

Masculine.

Helochares livornicus Kuwert, 1890: 38; subsequent designation by d’Orchymont (1939a: 154).

Body length ranging from 2.5–4.8 mm. Body shape oval in dorsal view, dorsoventrally slightly flattened, moderately convex in lateral view, with dorsal outline nearly evenly convex (Fig. 28); surface even and smooth, with usually shallow ground punctation (Fig. 28). Coloration usually dark brown seldom yellowish, uniform across body regions. Head trapezoid (Fig. 11G). Eyes relatively large, at most only slightly emarginated anteriorly, and not or only slightly projected from outline of head. Clypeus trapezoid, with anterior margin mesally emarginate; membranous preclypeal area visible when clypeus strongly emarginated. Labrum fully exposed. Mentum punctate or punctate laterally and medially obliquely striate; medial surface flat to depressed (Fig. 28C); anteromedial depression sometimes limited by low transverse carina. Antennae with nine antennomeres, with cupule slightly asymmetric and rounded. Maxillary palps slender, 1.2–1.5 × longer than width of head; maxillary palpomere 4 nearly 0.7 × length of maxillary palpomere 3; inner margin of maxillary palpomere 2 nearly straight, and outer margin curved along apical half. Pronotum evenly convex. Elytra with sutural striae, with outer margins slightly flared; ground punctures usually only shallowly marked, serial punctures absent and at least one median row of systematic punctures visible on each elytron (Fig. 28). Surface of prosternum usually flat, sometimes tectiform. Posterior elevation of mesoventrite with longitudinal carina; anapleural sutures sinuate, separated at anterior margin by distance similar to slightly shorter than anterior margin of mesepisternum. Metaventrite with posteromesal and posterolateral glabrous patches (Fig. 28C). Protibiae with spines of anterior row semi erect, relatively long, thick and sparse; apical spurs of protibiae relatively short and stout, not reaching apex of protarsomere 2. Metafemora with tibial grooves moderately developed; hydrofuge pubescence covering basal 4/5 of anterior surface of metafemora (Fig. 28C). Metatarsomeres 2–4 gradually decreasing in size, with two rows of spines on ventral surface; metatarsomere 2 slightly longer than 5, 5 shorter than 3 and 4 combined. Fifth abdominal ventrite emarginate at apex, with fringe of flat and stout setae. Aedeagus (Fig. 27B–D) with parameres at most only fused at base on dorsal surface; median lobe divided in dorsal and ventral plates; dorsal plate sclerotized along margins, medially membranous, membranes with papillae or denticles along apico-medial region; ventral plate as inverted Y, sometimes accompanied by basal median laminar sclerite; basal piece nearly as long as or longer than ventral length of parameres, always noticeable; gonopore not clearly visible.

Figure 28. 

Habitus Crephelochares spp. A–C Crephelochares nitescens: A dorsal habitus B lateral habitus C ventral habitus D Crephelochares cf. patrizii (image from Bird et al. 2017). Scale bars: 1 mm.

Among Old World acidocerines, Crephelochares is unique in the presence of sutural stria. The Neotropical Chasmogenus is the most similar genus, as they both share this character (along with the more distantly related Neotropical genus Primocerus). They can be differentiated by the number of antennomeres (eight in Chasmogenus, nine in Crephelochares) and by the form of the aedeagus (trilobed in Chasmogenus, Fig. 25; divided and further modified in Crephelochares, Fig. 27B–D). The configuration of the aedeagus in Crephelochares is quite unique in Acidocerinae, especially because of the configuration of the median lobe and its inner membranes.

Afrotropical: Angola, Benin, Botswana, Burundi, Cameroon, Democratic Republic of the Congo, Gabon, Gambia, Ghana, Guinea, Kenya, Liberia, Madagascar, Mauritius, Mozambique, Namibia, Niger, Nigeria, Rwanda, Senegal, Seychelles (Aldabra), Sierra Leone, Somalia, Republic of South Africa, Sudan, Tanzania, Uganda, Zambia, Zimbabwe. Australasian: Australia (New South Wales, Northern Territory, Queensland), Fiji (Vanua Levu, Viti Levu), New Caledonia, Papua New Guinea. Indo-Malayan: Cambodia, China (Guangdong, Hong Kong, Taiwan, Yunnan), Indonesia (Borneo, Java, Papua, Sulawesi, Sumatra), Laos, Malaysia, Sri Lanka, Thailand, Vietnam. Palearctic: Bosnia, Croatia, Greece, Israel, Italy, Japan, Serbia and Montenegro, Spain, Tunisia, Turkey; Fig. 4.

Archangelsky (1997: 55) reproduced the larval descriptions by Anderson (1976), who reared larvae from adults of Crephelochares nitescens (as Helochares nitescens) in laboratory conditions. According to Anderson (1976: 223), females lay between 18 and 25 eggs, “located below the surface of damp soil, in a mossy hollow constructed by the adult; the hollow was always of the same size and shape and lined inside with loose silk. Eggs were deposited at right angles to base of nest, each covered by strands of fine silk attached to floor, walls and adjacent eggs”. The larvae hatch in 5–7 days and are predaceous (Archangelsky 1997: 55). “The larvae would not pupate in damp tissue paper, but only in moss. […]. The larvae pupated naked in the upper moss or in curled decaying leaves” (Anderson 1976: 223). Complete development lasted 24–33 days. Fikáček (2003) provided a diagnosis, pointed out the incompleteness of the descriptions and drawings offered by Anderson (1976), and commented on the unusualness of the habit of laying eggs on the ground by hydrophilid standards.

As for the adults, ecological information is very scarce. According to Hebauer (1992), C. livornicus (Kuwert) was collected in stagnant water with decaying plants and C. orbus (Watanabe) was collected in a rice field. The recently described C. parorbus (Jia and Tang) was also recorded from stagnant waters (Jia and Tang 2018).

The only species for which immature stages are known is Crephelochares nitescens [from Australia; immature stages were originally described as Helochares nitescens by Anderson (1976)]. Anderson (1976) described the breeding method he used, the eggs and egg case, first and third instar larvae and pupa, as well as the entire life cycle. Archangelsky (1997: 55) reproduced Anderson’s (1976) findings.

Crephelochares was originally described as a subgenus of Helochares by Kuwert (1890: 38). In 1904, Ganglbauer established Crepidelochares without justification or explanation. Later, d’Orchymont (1919c: 148) synonymized Crephelochares with Chasmogenus keeping Chasmogenus as a subgenus of Helochares. In 1986, Fernández reinstated Chasmogenus as a genus, with Crephelochares as a junior synonym. Subsequent authors alternately either treated Crephelochares as a subgenus or junior synonym. Hebauer (1992) removed Crephelochares from synonymy with Chasmogenus, and established it as a subgenus of Chasmogenus, discussing morphological features in support of this view, which he maintained in subsequent works (Hebauer 1995). However, Hansen (1991, 1999b) viewed the differences in antennomeres and the aedeagal complexity as “rather subtle” and maintained the two names as synonymous without subgeneric division. The phylogenetic analysis by Short et al. (2021), together with the morphological evidence offered by Hebauer, resulted in the recognition of the generic status of Crephelochares.

There are 29 species of Chephelochares described to date; some of the older species have long lists of synonyms. The most comprehensive treatment for the genus was by Hebauer (1992); the genus was then considered as a subgenus of Chasmogenus.

Crephelochares abnormalis (Sharp), C. africanus (d’Orchymont), C. balkei (Short)*, C. irianus (Hebauer)*, C. livornicus (Kuwert), C. mauritiensis (Balfour-Browne), C. molinai (Hebauer)*, C. nitescens (Fauvel), C. orbus (Watanabe), C. paramollis (Hebauer)*, C. patrizii (Balfour-Browne), C. punctulatus (Short)*, C. ruandanus (Balfour-Browne), C. rubellus (Hebauer)*, C. rusticus (d’Orchymont), C. rutiloides (d’Orchymont), C. rutilus (d’Orchymont), C. szeli (Hebauer)*. For species marked with an asterisk, paratypes were available.

Hebauer 1992: diagnosis, key to species, diagnoses, descriptions for 22 species, and genitalia drawings for 19 of them; Hebauer 1995: one new species from Namibia; Watts 1995: revision of the Australian species of the genus; Short 2010: revision of the species from the Southwest Pacific islands, describing two new species from Fiji and newly recording C. nitescens (Fauvel) for New Caledonia; Devi et al. 2016: redescription and lectotype designation for C. abnormalis (Sharp) with a discussion on its distribution and morphological variation; Short et al. 2021: generic status and phylogenetic placement.

Masculine.

Crucisternum ouboteri Girón & Short, 2018: 121; by original designation.

Small beetles, body length 2.0–2.5 mm. Body shape elongated oval in dorsal view; moderately convex in lateral view (Fig. 29). Color orange brown to dark brown. Head trapezoid. Eyes moderate to small, projected from outline of head. Clypeus trapezoid, with anterior margin broadly and roundly emarginate. Labrum fully exposed. Mentum with lateral oblique ridges; anterior median depression marked by transverse carina (Fig. 29C). Antennae with nine antennomeres, with cupule only slightly asymmetrical and rounded. Maxillary palps moderately long, slightly longer than width of head (Fig. 29A). Elytra without sutural striae, with outer margins of elytra slightly flared; serial punctures, ground punctures and systematic punctures similar in size and degree of impression, either shallow or rather sharply marked; all punctures seemingly arranged in rows (Fig. 29A). Prosternum with well-developed median, longitudinal, laminar carina (Fig. 29C). Posterior elevation of mesoventrite with a strongly produced, anteriorly pointed transverse ridge, longitudinally carinate (Fig. 14C); anapleural sutures sinuate, separated by distance nearly 0.6 × width of anterior margin of mesepisternum. Metaventrite densely pubescent, except for median and postero-lateral glabrous patches (Fig. 29C). Protibiae with spines of anterior row long and thick; apical spurs of protibiae short and stout, almost reaching apex of protarsomere 2. Metafemora covered by hydrofuge pubescence along basal 4/5 (Fig. 29C). Metatarsomeres 2–4 gradually slightly decreasing in size; metatarsomere 5 slightly longer than 2; ventral coverage of tarsomeres composed of fine and spiniform setae. Fifth abdominal ventrite apically rounded, truncate, or slightly emarginate, without stout setae. Aedeagus trilobate (Fig. 30A–E); basal piece 0.2–0.25 × the length of parameres; median lobe with well-developed lateral basal apodemes, and acute to narrowly rounded apex; parameres nearly as long as median lobe, with outer margins usually sinuate; gonopore situated distad of midlength of median lobe.

Figure 29. 

Habitus of Crucisternum ouboteri A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.

Figure 30. 

Aedeagi of Crucisternum, Ephydrolithus, and Globulosis spp. A C. ouboteri B C. toboganensis C C. sinuatus D C. vanessae E C. queneyi F E. teli G E. spiculatus H E. ogmos I E. minor J G. flavus. Scale bars: 0.25 mm.

Although Crucisternum is generally unremarkable dorsally from other small-bodied Neotropical acidocerines, several sternal features are strikingly unique and easily separate the genus from all others. The strongly developed prosternal carina found in the genus, combined with the cruciform shape of the posterior elevation of the mesoventrite (formed by the fusion of both transverse and longitudinal ridges), is unique for this genus in the subfamily. Crucisternum is most likely to be confused in samples as a very small Chasmogenus but can also easily be distinguished from that genus by the lack of sutural striae.

Neotropical: Brazil (Minas Gerais, Pará), French Guiana, Guyana, Suriname, Venezuela; Fig. 5.

All species of the genus are associated with forested streams, usually along margins that contain ample detritus. A single specimen of C. ouboteri was collected at a black light trap.

Immature stages are not known for the genus.

The genus was only recently described.

There are seven species currently known.

Holotypes and paratypes of all the known species were examined for this study.

Girón and Short 2018: original description of the genus and all its known species; Short et al. 2021: phylogenetic placement.

Masculine.

Ephydrolithus hamadae Girón & Short, 2019: 130; by original designation.

Small beetles, body length 1.8–3.3 mm. Body shape oval in dorsal view, moderate to strongly convex in lateral view (Fig. 31); with ground punctation usually moderately marked. Color yellowish brown to dark brown, usually uniform across body regions (Fig. 31). Shape of head trapezoid. Eyes relatively small, at most only slightly emarginated anteriorly, usually moderately projected from outline of head. Clypeus trapezoid, with anterior margin from broadly to only slightly emarginate. Labrum fully exposed. Mentum with strong median anterior depression sometimes limited by low transverse carina; surface of mentum mostly smooth and undulated. Antennae with nine antennomeres; cupule slightly asymmetric, with rounded outline. Maxillary palps short, nearly 2/3 width of head, and stout (Fig. 31C); inner margin of maxillary palpomere 2 nearly straight, outer margin strongly curved along apical half. Elytra without sutural striae, and only rarely with impressed striae; ground punctures moderate to sharply marked, uniformly and rather densely distributed; systematic punctures slightly larger and deeper than remainder punctures; serial punctures usually not clearly differentiated; outer margins of elytra only slightly flared (Fig. 31A, D). Prosternum flat, sometimes only slightly elevated along longitudinal midline (Fig. 31C). Posterior elevation of mesoventrite either with transverse ridge, or with well-developed tooth that extends anteriorly as longitudinal carina; anapleural sutures concave, separated at anterior margin by distance nearly 0.3 × anterior margin of mesepisternum. Metaventrite densely pubescent, except for large median teardrop-shaped glabrous patch (Fig. 31C, F); anteromedian area of metaventrite with a deep and narrow transverse depression before anterior intercoxal process. Protibiae with spines of anterior row hair-like, semi erect, relatively long and thick (Fig. 31C). All tarsomeres bearing long apical hair-like setae on dorsal face, and two lateral rows of hair-like spines on ventral face of tarsomeres 2–4. Posterior femora mostly glabrous, with few scattered setae along basal half to basal 2/3, with hydrofuge pubescence along anterodorsal margin (Fig. 31C, F); tibial grooves well-developed, sometimes covered by hydrofuge pubescence. Fifth abdominal ventrite apically truncate, with stout setae. Aedeagus trilobed (Fig. 30F–I), with outer margins convex, straight or sinuate, with basal piece 0.45–0.9 × length of parameres; median lobe somewhat triangular in shape, with well-developed lateral basal apodemes; apex of median lobe widely to narrowly acute, sometimes “pinched”; parameres nearly as long as median lobe; well-developed gonopore, preapically situated.

Figure 31. 

Habitus of Ephydrolithus spp. A–C E. hamadae: A dorsal habitus B lateral habitus C ventral habitus D–F E. ogmos: D dorsal habitus E lateral habitus F ventral habitus. Scale bars: 1 mm.

Ephydrolithus can be distinguished from most Neotropical acidocerines by their mostly glabrous metafemora. From other genera exhibiting the same condition, such as Quadriops (Girón and Short 2017), Ephydrolithus can be distinguished by the entire (as opposed to divided; Fig. 11C) eyes; from Tobochares (Kohlenberg and Short 2017), Ephydrolithus can be differentiated by the number of antennomeres (nine in Ephydrolithus, eight in Tobochares).

Neotropical: Brazil (Bahía, Minas Gerais); Fig. 5.

All known species are exclusively associated with rock seepages (e.g., Fig. 9; Girón and Short 2019).

Immature stages are not known for the genus.

Ephydrolithus was only recently described.

In the etymology section of the original publication, Girón and Short (2019) indicate that the genus name is neuter, which is erroneous. The name is masculine, which is the gender for the Greek word lithos, the last component of the genus name. Four species of Ephydrolithus have been described until now, all of them from southeastern Brazil.

Holotypes and paratypes of all known species were examined for this study. We have also seen specimens of additional undescribed species.

Girón and Short 2018: original description of the genus and all its known species; Short et al. 2021: phylogenetic placement.

Masculine.

Globulosis hemisphericus García, 2001: 153; by original designation.

Small beetles, body length 1.9–2.3 mm. Body shape rounded in dorsal view, strongly convex in lateral view (Fig. 32). Surface of head, pronotum and elytra smooth, with moderate to shallow ground punctation. Coloration yellow to dark brown, uniform along body, with paler mouthparts and tarsi (Fig. 32). Shape of head relatively oval. Eyes relatively small, anteriorly emarginated (Fig. 32B), not projected from outline of head. Clypeus trapezoid, with anterior margin mesally broadly emarginate. Labrum fully exposed. Mentum with anterior depression limited by low transverse carina; surface of mentum only slightly striate. Antennae with eight antennomeres, with cupule only slightly asymmetric and rounded in outline. Maxillary palps slender, slightly shorter than width of head (Fig. 32C). Pronotum evenly convex. Elytra without sutural or other distinct striae, with outer margins slightly flared; elytral ground punctation shallow to moderate, uniformly distributed (Fig. 32). Surface of prosternum flat. Mesoventrite with transverse ridge, usually elevated medially into acute tooth (Fig. 32C); anapleural sutures concave, separated at anterior margin by distance nearly as width of anterior margin of mesepisternum. Metaventrite uniformly covered by hydrofuge pubescence, with small, longitudinal posteromesal glabrous patch, and reduced posterolateral glabrous patches (Fig. 32C). Protibiae with spines of anterior row long, thick, semi erect and sparse; apical spurs of protibiae short and of moderate thickness. Metafemora with moderate tibial grooves; hydrofuge pubescence covering basal 4/5 of anterior surface (Fig. 32C). Tarsomeres 1–4 ventrally with rows of long and thick setae. Metatarsomeres 2–4 gradually decreasing in size, 5 nearly as long as 2–4 combined. Fifth abdominal ventrite with small truncation at apex, with fringe of flat and stout setae. Aedeagus trilobed (Fig. 30J); with short basal piece, less than 1/3 length of parameres; median lobe wider than width of parameres; gonopore well differentiated.

Figure 32. 

Habitus of Globulosis flavus A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.

Globulosis is among the smallest acidocerines. Its small size along with very round and convex body shape, sets it apart from all other acidocerines known to date.

Neotropical: Brazil (Amazonas, Pará), Colombia, Guyana, Suriname, Venezuela; Fig. 5.

The genus is most commonly found along the margins of small, sandy forested streams, especially with vegetated margins. However, a few specimens have been taken in shallow swamps.

The immature stages of Globulosis remain unknown.

García (2001) described the genus with one species, and placed it in its own tribe (Globulosina, now synonymized with Acidocerinae). The genus was revised in 2017 by Short et al., who described one new species and examined new material that greatly expanded the range of the previously known species.

There are two described species of Globulosis. One female specimen from Colombia has been left unidentified as it could not be reliably assigned to any species. Because of the extremely uniform external morphology in the genus, the male genitalia is the most reliable feature for species recognition. Based on additional material we have examined the genus appears to be more broadly distributed in the Amazon region than as currently published.

The holotype, along with several additional specimens of Globulosis hemisphericus García, and the holotype and paratypes of G. flavus Short, García & Girón were examined in this study.

García 2001: genus description, monotypic; Short et al. 2017: description of one new species from Venezuela, range expansion for type species; Short et al. 2021: phylogenetic placement.

Feminine.

Helopeltis larvalis Horn, 1873: 137; by monotypy.

Medium sized beetles, body length 4–7 mm. Body shape oval in dorsal view, dorsoventrally flattened, with dorsal outline nearly straight along medial third in lateral view (Fig. 33); surface even and granulate. From yellowish, orange brown to dark brown in coloration, usually with patterns along elytra, with different areas of head and pronotum darkened. Shape of head somewhat trapezoid (Fig. 11L). Anterior corners of frons extended laterally and posteriorly, emarginating anterior margin of eyes. Eyes of moderate size, somewhat oval, anteriorly deeply emarginated, not projected from outline of head. Clypeus somewhat pentagonal, laterally explanate, with anterior margin usually straight (Fig. 11L). Labrum concealed by clypeus (Fig. 11L). Mentum with surface variably sculptured, usually with oblique and transverse striae (Fig. 33C). Antennae with eight antennomeres, with cupule strongly asymmetric and oval in outline. Maxillary palps slender, slightly longer than greatest width of head; inner margin of maxillary palpomere 2 weakly and evenly curved, and outer margin weakly curved along apical third (Fig. 33C). Pronotum with surface of lateral areas flat. Elytra without sutural striae, with outer margins laterally explanate; serial punctures clearly aligned in longitudinal rows (Fig. 33A). Scutellar shield U-shaped. Surface of prosternum flat, to medially bulging, smooth to irregularly sculptured. Posterior elevation of mesoventrite only weakly bulging, with pair of lateral, longitudinal, low ridges; anapleural sutures nearly parallel along anterior section, separated anteriorly by distance slightly shorter than anterior margin of mesepisternum. Metaventrite uniformly covered by hydrofuge pubescence, with medial, narrow, and slightly carinate glabrous patch; posterolateral glabrous patches reduced. Protibiae with spines of anterior row short and semi erect; apical spurs of protibiae reduced, much shorter than protarsomere 1. Metafemora with tibial grooves moderately developed; hydrofuge pubescence covering 5/6 of anterior surface (Fig. 33C). Tarsomeres 1–4 ventrally densely covered by setae; metatarsomere 2 longer than 3 and 4 combined, 1 nearly as long as 3, and 5 nearly as long as 2–4 combined. Fifth abdominal ventrite apically emarginate, with fringe of flat and stout setae. Aedeagus divided (Fig. 34), parameres separated from each other for most of their lengths; median lobe divided in dorsal and ventral plates; dorsal plate usually strongly sclerotized; ventral plate bilaterally bifurcated, forming thick lateral lobes along apical region; basal piece nearly 0.2 × the length of parameres, always noticeable; gonopore not clearly visible.

FIgure 33. 

Habitus of Helobata spp. A–C H. larvalis: A dorsal habitus B lateral habitus C ventral habitus D H. quatipuru (from Clarkson and Almeida 2018) E H. amazonensis (from Clarkson and Almeida 2018) F H. pantaneira (from Clarkson et al. 2016). Scale bars: 1 mm.

Figure 34. 

Aedeagi of Helobata spp. A, B H. pantaneira (from Clarkson et al. 2016): A dorsal view B lateral view C, D H. quatipuru (Clarkson and Almeida 2018) A dorsal view D lateral view E H. sp. (Ecuador), dorsal view. Scale bars: 0.5 mm.

Helobata is one of the most conspicuous genera of acidocerines, especially in the New World. The flattened and broadly explanate body shape and concealed labrum, accompanied by granulose surface, long and slender maxillary palps and well-defined elytral serial punctures, are quite unique in the subfamily. The only genus that shares some of these features is Helopeltarium, except that the latter has short maxillary palps, smooth surface and lacks serial punctures along the elytra. The configuration of the aedeagus (Fig. 34), in particular the thickness of the lateral lobes of the ventral plate of the median lobe, is also unique among acidocerines.

Nearctic: United States (California, Florida, Louisiana, Mississippi, North Carolina, South Carolina, Texas, Virginia). Neotropical: Argentina, Bolivia, Brazil (Amazonas, Ceará, Mato Grosso, Mato Grosso do Sul, Pará, Rio de Janeiro, Roraima), Cuba, Guatemala, Mexico, Paraguay, Suriname, Venezuela; Fig. 5.

Species of Helobata occur primarily in open habitats with abundant vegetation. According to Clarkson et al. (2016), specimens of Helobata are uncommonly encountered and occur in marshes, swamps, and ponds, most often in small numbers, although they are rarely found in modest amounts (dozens of individuals; Short, pers. obs.). According to Archangelsky (1997), they can be found in slow moving creeks or rivers, living among the littoral vegetation or on floating plants. They are attracted to lights. Females have been observed carrying their egg cases attached to the ventral side of their abdominal ventrites (Archangelsky 1997).

The larva (first instar) and egg case are only known for Helobata larvalis; these immature stages were described by Spangler and Cross (1972). A differential diagnosis of the first instar larva was provided by Fikáček (2003).

This genus was described by Horn (1873) under the name Helopeltis, which was preoccupied by Helopeltis Signoret, 1858 (Hemiptera). Bergroth (1888) proposed the name Helobata as a replacement name for Helopeltis Horn, whereas Cockerell (1906a) proposed the name Helopeltina. Helobata has priority, so it is the currently valid name for the genus, which was revised by Fernández and Bachmann (1987).

There are 13 species of Helobata described to date. The type species, Helobata larvalis (Horn), has generally been known under the name Helobata striata (originally published as Hydrophilus striatus Brullé, 1841: 58, which is a primary homonym of Hydrophilus striatus Say, 1825 [now Berosus striatus (Say)]; therefore unavailable. The name Helobata larvalis (Horn) was then reinstated by Hansen (1991: 293). Photos of a syntype of Helopeltis larvalis (Horn) are available at https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:101 (accessed 9 January 2021). The external morphology of members of Helobata is very homogeneous. Some variation can be observed in the shape of the clypeus (e.g., Fernández 1987; Clarkson et al. 2016). Helobata is the only Neotropical genus truly widespread in the New World, as it ranges from southeastern North America, all the way to Argentina and Southern Brazil.

Helobata cuivaum García (paratype), H. larvalis (Horn), and H. lilianae García (paratype).

Horn 1873: original description of the genus and the type species; Spangler and Cross 1972: description of egg case and first instar larva; Fernández and Bachmann 1987: review of the genus, description of four new species from Argentina, Brazil and Paraguay; García 2000: three new species from Venezuela; Makhan 2007: two new species from Suriname; Clarkson et al. 2016: two new species from Brazil, review and new country records of Brazilian species; Clarkson and Almeida 2018: new records from Brazil; Short et al. 2021: phylogenetic placement.