Taxonomic revision of the genus Oplognathus MacLeay, 1819 (Coleoptera: Scarabaeidae: Rutelinae: Rutelini)

The genus Oplognathus MacLeay, 1819 is revised based on type material of two of the three described species and scattered additional material from several collections around the world. The diagnostic characters of the genus are confi rmed, distinguishing it from other Brazilian Areodina mainly by: quadrangular clypeus with trilobate apex in males, rounded in females, extending beyond labrum in both sexes; mandibles with three distinct teeth; maxillae with six teeth; antenna with 10 antennomeres; 10 elytral striae; mesoventral process present; and asymmetrical parameres. The genus and all three species are redescribed, and the female of Oplognathus bahianus Ohaus, 1912 is described for the fi rst time. We consider Oplognathus helmenreichi var. maculicollis Ohaus, 1914 an unavailable infrasubspecifi c taxon that is conspecifi c with Oplognathus helmenreichi Ohaus, 1905; its distribution is updated, and the different spelling of the specifi c epithet is discussed. A neotype is designated for Oplognathus kirbii MacLeay, 1819 since the holotype is currently considered lost. Additionally, an identifi cation key and a distribution map are included.

Oplognathus is considered a rare genus with few specimens represented in collections, and as other areodines, represented by few species: Oplognathus bahianus Ohaus, 1912, O. helmenreichi Ohaus, 1905and O. kirbii MacLeay, 1819(MacLeay 1819Ohaus 1934;Blackwelder 1944;Machatschke 1972;Krajcik 2007). Species of Oplognathus are distributed in the Brazilian Atlantic Forest, occurring from southern Bahia to northern Paraná states (Ratcliffe & Jameson 1989). Most of the known specimens were collected in the 19 th and 20 th centuries, and there are very few recently collected specimens. In species of Oplognathus, the most peculiar diagnostic character of adults is the trilobed clypeus of males. In contrast, females can be easily confused with small females of Areoda. When describing Oplognathus for the first time, MacLeay (1819) pointed out the following characteristics: mandible with tridentate apex in the inner margin, maxillae with six teeth, labial palpi dorsally inserted on mentum, apex of mentum rounded, clypeus subquadrangular, short and trilobed. The biology of the genus is unknown, except for the report by Grossi & Vaz-de-Mello (2015) of collecting of O. bahianus in light traps, indicating nocturnal habits. Jameson (1990) presented the only up to date morphological phylogenetic analysis for Areodina. In her analysis the monophyly of the subtribe was confirmed and Oplognathus, Areoda and Byrsopolis formed a clade, sister group to the Central and North American genera clade. According to Carvalho & Grossi (2018), Oplognathus and Areoda are differentiated by the presence of a forward-projecting mesoventral process, which is absent in both Byrsopolis and Moronius (hypothesizing that Moronius also belongs to this clade). According to Jameson (1990), Oplognathus differs from other Areodina because of three diagnostic characteristics: 1) clypeus ventrally produced beyond labrum, and with weakly trilobed apex in males; 2) presence of mesoventral process; and 3) asymmetrical parameres. However, the latter two characteristics are also observed in Areoda, but with a hook-like projection in parameres, the mesoventral process is relatively longer and the asymmetry of the parameres much more evident in Areoda. To a much lesser degree, such paramere asymmetry is also observed in Byrsopolis. The clypeus projecting beyond the labrum may be the best feature to distinguish among the three genera, a character present in both sexes.
In this present contribution we revise the genus Oplognathus based on external morphology. All species are included, and illustrations of the external morphology, the mouth parts, and the male genitalia are presented. A distribution map of the species is given for the first time, as well as an identification key for the three species of the genus.

Taxonomic material
A total of 37 adult specimens from 12 collections were studied, including type material found. The material examined in the present study is housed in the following collections:

Measurements
Measurements were obtained with a pachymeter. The body length was measured from the apex of the head to end of the elytra. The body width was measured at the middle of the pronotum. The puncture size, and the density of punctures follow Jameson (1990Jameson ( , 1997
THorax. Pronotum convex, transverse, about 1.8 times wider than longer, beaded; pronotal bead incomplete posteriorly at middle; surface varying from sparse to densely punctate; punctures small to moderate; maculae varying from two distinct anterolateral spots to two complete elongated maculae; some specimens with spots and maculae obsolete or absent. Each elytron with 10 distinctly punctate striae, punctures fine to moderate, interstriae almost smooth, punctures visible from 10× of magnification; humeri rounded, smooth; elytral apex straight. Hind wings full developed with a group of setae at AA 1+2, setae long and fine, longer than width of first axillar sclerite; AP 3+4 softly setose at base, with fine and minute setae; R 3+4 sclerotized, disc with a distinct row of short setae. Mesoventral process acute, elongated, but never extended beyond anterior procoxal base (Fig. 8). Metafemur with anterior and posterior margins rounded, distinctly developed that other femora, with at least twice the mesofemoral width. Protibia tridentate, teeth reducing in size from apex to base, proximal tooth sometimes obsolete; inner apex with one tiny spur; ventral surface distinctly dilated, convex. Mesotibia with surface rugose, and two oblique carinae: proximal carina with 2-7 spinules, and distal carina with 4-9 spinules, distal carina longer; mesotibial apex truncate with 7-13 spinules and two spurs, inner spur slightly longer. Metatibia wider than mesotibia, with inner margin distinctly rounded, apical spinules varying from 14-22; spurs distinctly short, and flattened, apex less acute than spinules; proximal carina with 2-8 spinules and distal carina with 6-11 spinules. Protarsomere V thickened; inner claw stronger with a basal obtuse tooth. Meso-and metatarsomere ornamented with lateral setae, and inner apical spinules. Meso-and metatarsal claws curved, simple, unequal in thickness; unguitractor plate present with two apical setae.
Head. Apex rounded, never with projections; antennal club distinctly smaller.

Nomenclatural history
Oplognathus was described by MacLeay (1819) without 'H' at the beginning of the name, but later Burmeister (1844) redescribed the genus as "Hoplognathus", justifying that it would be the correct spelling for the name. Lacordaire (1856) also pointed the "error" of MacLeay, and uses Hoplognathus as a valid name, indicating "Aplognathus" as original wrong spelling, but not specifying the cause of the error. Since then, the name Hoplognathus has been widely used, including the description of the new species, generating more synonyms, such as Hoplognathus bahianus and Hoplognathus helmenreichi. Only Machatschke (1970) comments that Hoplognathus is a synonym, but when using Oplognathus, the spelling appears as "Oplongnathus". Already in his catalogue, Machatschke (1972) cites "Oplognathus" using the original spelling, which proves to be a typing error in the previous publications. Ratcliffe & Jameson (1989) note this fact and show the correct use "Oplognathus MacLeay (not Hoplognathus as in Burmeister 1844; Ohaus 1918Ohaus , 1934Blackwelder 1944)", because according to Article 23 (ICZN 1999), the Principle of Priority, the oldest name should be used. In the original description, MacLeay (1819) does not detail the etymology of Oplognathus, but the Hoplo prefix, from the Greek Hoplon, means 'any tool or implement of armour and shield' while Gnathus, from the Greek, means 'mandible, mouth', possibly due to the distinct shape of the clypeus of the males. Perhaps, this explains the insistence of later authors (Burmeister 1844;Lacordaire 1856) to use the spelling Hoplognathus, instead of Oplognathus, as correct. However, as there is no written indication of this, and the addition of 'H' is not a clear, obvious and necessary correction of the name, Oplognathus must be maintained, following the original description and not its subsequent spelling (ICZN 1999, Art. 33).
Although Burmeister corrected the name of the genus, this does not mean that Ohaus intended to describe Oplognathus bahianus and Oplognathus helmenreichi in a genus other than Oplognathus. Thus, the author's name is written here without brackets, since the species is basically in its original combination.
Oplognathus kirbii was cited by Laporte (1840) as Oplognathus kirbyi and since then, both spellings were widely used, in addition to Hoplognathus kirbii and Hoplognathus kirbyi, it is common to find four spellings for this species throughout the literature. There are no details for replacing 'i' with 'y', but we can suppose Laporte (1840) to make this change on the assumption that MacLeay intended to honour the naturalist William Kirby. ICZN (1999, Article 58.2) states that the use of 'i' and 'y' are 'variant spellings' deemed to be identical. However, as MacLeay (1819) makes the description with no detail about etymology, it is prudent to keep the original spelling Oplognathus kirbii and not to use the subsequent spellings (ICZN 1999, Art. 33).
Oplognathus helmenreichi was described for the first time based on a single specimen in the collection of W.J.C. Weber by Ohaus (1905) with this spelling (for the specific epithet) and the locality Buenos Aires, Argentina. Later, Ohaus wrote that he found (Ohaus 1914a: 22) several specimens of this species in the Museum of Vienna, but he described them as a variety "var. maculicollis". These specimens were labelled "Helmr.", realizing that the name of the collector was Helmreichen and not Helmenreich, as published in Ohaus (1905). Although Ohaus (1914a) has described the variety as "Hoplognathus helmreicheni var. maculicollis" in the original publication, the correct name is Hoplognathus helmenreichi var. maculicollis (as written on the original label). In this case, Ohaus (1914a) made an unjustified emendation almost 10 years after the original publication of the species, not being recognized by the Code to validate a name (ICZN 1999, Art. 19.1, 33.2). Still, the latter spelling is used as valid, violating the Principle of Priority (ICZN 1999, Art. 23.9).
abdomen. Pygidium transverse, subtrapezoidal, surface sparsely setose, setae fine, and medial-posteriorly disposed. Ventrites in general aspect convex, ventrites II-IV with a slight central concavity, and with sparse setae and sparse punctures posteriorly. Parameres transverse, broader, apex V-shaped, left side slightly shorter, base rounded; left side of parameres expanded in lateral view, expansion parabolic, and with two apical lobes, almost with same length; right side of parameres sinuous, with two apical lobes, outer lobe shorter; paramere base almost straight, with discrete sinuosity (Figs 5a-c, 7a-d).

Type locality
Brazil.

Remarks
The holotype of Oplognathus kirbii MacLeay, 1819 is currently considered lost, and could not be traced in any of the likely collections. A neotype is designated to stabilize the nomenclature. We selected the oldest historical specimen, one that was received by NHMUK with Bowring's collection in 1863 [accession number 47]. The neotype fits the drawing of Guérin-Meneville (1844), the earliest illustration of the species (25 years after the description) which helps ensure that we selected the correct taxon. MacLeay (1819) provided only "Brazil" as the type locality. Since O. kirbii is a Brazilian endemic it is not a problem that the collecting data of the neotype are illegible.
Oplognathus kirbii can be found in the mountainous regions of the states of Rio de Janeiro, São Paulo, Espírito Santo and Minas Gerais, besides being recorded in literature for the state of Paraná (specimens from Paraná have not been confirmed here), inhabiting humid areas of the Atlantic Forest, unlike the other species of the genus, found in areas of Mata Seca in the north of Minas Gerais. Ohaus, 1905 Figs 1c-e, 2b-d, 3c-d, 4i-m, 6, 7e-h, 8c, f, 9 Hoplognathus helmenreichi Ohaus, 1905
Colour. General aspect metallic dark green and reddish brown; head, pronotum, legs and venter metallic green, elytra reddish brown.

Male variation
Size: total length: 17.2-19.0 mm; width across prothorax: 7.5-9.1 mm. General aspect orange-brown; head, pronotum and scutellar plate may have yellowish maculae (Fig. 1d-e). Suture frontoclypeal vary in the degree of sinuosity. Pronotum can be more or less truncate at sides. Surface of mesofemur varies from moderately to densely punctate. Mesotibia with proximal and distal carina marked by 4-7 spinules; apex truncate with 7-13 spinules. Metatibia with 14-22 spinules in the apex, distal carina with 5-11 spinules, and proximal carina with 5-8. Parameres vary from parabolic curvature of the aedeagus to the truncate curvature, as well as, in the degree and shape of lateral expansion, it can be longer and more parabolic (Figs 6d-f, 7e-h).
Female (Fig. 1e) Similar to males in general aspects, differentiating in the following aspects: pronotal maculae more elongate; clypeus rounded; frontoclypeal suture distinct, with central curvature; antennal club 0.7× smaller than in males, 1.5× longer than antennomeres 2-7 combined. Pronotum with parallel sides and anterior angles more rounded. Elytral epipleuron slightly rounded, distinct depression above epipleuron. Protarsomere I as long as protarsomeres II-IV combined.

Type locality
Oplognathus helmenreichi was originally described from Buenos Aires (Argentina) (Ohaus 1905), and this locality was later contested by the author (Ohaus 1914a) while describing the variety, O. helmenreichi var. macullicolis. This species can actually be found in the north and northeast of Minas Gerais state in the Jequitinhonha River Valley (Ohaus 1914a). Accordingly, after the examination of three more males from the same region, we agree with Ohaus (1914a) and disregard the occurrence of O. helmenreichi in Argentina.

Remarks
We consider the type of Oplognathus helmenreichi a holotype since Ohaus (1905) mentions only a single specimen. For Oplognathus helmreicheni var. maculicollis Ohaus (1914a) had multiple specimens available. ICZN (1999, Article 45.6.1.) states that a name "is infrasubspecific if its author expressly gave it infrasubspecific rank, or if the content of the work unambiguously reveals that the name was proposed for an infrasubspecific entity". Furthermore, the Article 45.6.4. (ICZN 1999) clarifies that a name "is subspecific if first published before 1961 and its author expressly used one of the terms "variety" or "form" (including use of the terms "var.", "forma", "v." and "f."), unless its author also expressly gave it infrasubspecific rank, or the content of the work unambiguously reveals that the name was proposed for an infrasubspecific entity, in which case it is infrasubspecific". In the time Ohaus described Oplognathus helmenreichi var. maculicollis he already clearly separated between species, subspecies and varieties as an article from the same year (see Ohaus 1914b) shows where he described new taxa on the species, subspecies and infrasubspecific levels. Therefore, Oplognathus helmenreichi var. maculicollis is an unavailable name. Although the pair of syntypes of O. helmenreichi var. maculicollis examined have some distinct characteristics of the holotype -such as yellowish colour, smaller size, less dense punctures and the male genitalia almost parallel sided, the other specimens examined show many similarities both with the syntypes and with the holotype. The variation of these characteristics was also observed within the other species of the genus. Despite these variations, mouthpart characters (like mentum shape, maxillary palpus shape) and mesoventral process remained constant in the eight specimens examined. Thus, Oplognathus helmenreichi var. maculicollis does not present a unique combination of character states that justify validating it to species or subspecies status.
No other specimen of O. helmenreichi was subsequently collected in Buenos Aires, or anywhere else in Argentina (Ohaus 1914a). One part of the material of O. helmenreichi var. maculicollis was labelled "Helm., Brasilia, XXII, 1853" and the other part "Serra do Grão Mogor, 1846" [Municipality of Grão Mogol, Minas Gerais]. Ohaus (1914a) then made it clear that the most probable locality of this species would be the north of Minas Gerais State (Grão Mogol) and not Buenos Aires, corresponding to the known distribution of the genus. Thus, we agree with Ohaus (1914a) and disregard Buenos Aires as a locality for this species, as well as for the genus Oplognathus. One male of the examined material is labelled as being from Curitiba, Paraná, South of Brazil, but the origin is doubtful, since this single specimen was found in a didactic collection of the Federal University of Paraná. Ohaus, 1912Figs 1f-g, 2a, 3b, 4e-h, 5d-f, 7i-m, 8b, e, 9 Hoplognathus bahianus Ohaus, 1912: 650. Hoplognathus bahianus -Ohaus 19181934: 42 (catalogue). -Blackwelder 1944. Oplognathus bahianus -Machatschke 1972: 5 (catalogue). -Krajcik 2007: 90 (catalogue).
Colour. General aspect with dorsal surface yellow gold and ventral surface metallic green; head, legs, and pygidium from cooper to reddish brown with metallic green reflections.
abdomen. Pygidium subtrapezoidal, sparse setae disposed in the margins, disc glabrous. Ventrites with surface sparsely setose posteriorly in the ventrites II-IV, and restricted to the lateral of ventrite VI, moderate punctuation. Parameres transverse, apex emarginated like V-shaped, with the left side distinctly shorter and broader, the right side slightly sinuous, base notched, concave; right lateral paramere divergent, straight, toward the apex with a concavity; apex with an only oblique lobe, transverse and anterior face straight; left lateral paramere broadly rounded and expanded ventrally, long expansion,  Ohaus, 1905 (ZMHB). i-m. O. bahianus Ohaus, 1912 (CERPE). Scale bar = 1 mm. apically of two lobes, external lobe projecting outwardly; base of parameres sinuous with median recess in V-shape ( Fig. 5d-f).

Male variation
Size: total length: 20.0-20.8 mm; width across prothorax: 10.0-10.5 mm. Frontoclypeal suture can be slightly sinuous. Mentum can have the anterior margin more or less curved, but all specimens show the notched type; mentum vary from 1.3-1.8× longer than frons. Pronotal and elytral punctation are distinctly marked, but one specimen has them very smooth. Surface on the scutellar plate varies from sparsely to moderately punctate. Mesoventral process is predominantly short with a rounded apex, one specimen has it more acute. Apex of protibia vary from 9-12 setae. Proximal carina of mesotibia varies by 2-3 spinules, and the distal carina varies by 5-9 spinules; apex truncate with 9-13 spinules. Metatibia with 18-20 spinules in the apex, distal carina with 7-11 spinules, and proximal carina with 3-5 spinules. Parameres vary in the degree of lateral inclination, lobes of parameres may be more or less pronounced, the lateral projections vary in length (Fig. 7i-m).

Type locality
Brazil. Bahia: [Santo Antônio da Barra], currently the municipality of Condeúba (Fig. 9).  Ohaus, 1912 (ZMHB). c, f. O. helmenreichi Ohaus, 1905 (CERPE). Scale bar = 1 mm. Ohaus (1912) did not state the number of specimens and therefore, we consider the single type specimen as a syntype. Oplognathus bahianus is the most distinctive species of the genus, with the males presenting a strongly trilobed clypeus. However, this character does not fit the original diagnosis of the genus (based on the type species O. kirbii), where the clypeus was described with this character being less evident. Although being a secondary sexual character, the clypeus has been used as the main diagnostic character of the genus. After this study, despite concerning only one sex, the trilobed cypleus is the best character to distinguish O. bahianus. Another relevant character to distinguish this species is the mesoventral process, which is not salient and simply rounded, vs acute and salient in the two other species.
Oplognathus bahianus was described by Ohaus (1912) from Santo Antônio da Barra in Bahia. This locality received the denomination of Condeúba in 1889, and is located in the south-central region of the state in the Bahia Semiarid Region, near the north of Jequitinhonha Valley. This species has the northernmost distribution in Brazil, being also found in the north of Minas Gerais in the Jequitinhonha Fig. 9. Geographic distribution of Oplognathus MacLeay, 1819.

Discussion
The genus Oplognathus is revised in this paper, with a redescription of the three species. The female of Oplognathus bahianus is described for the first time. The diagnostic characters of the genus are confirmed, distinguishing it from other Brazilian Areodina. Oplognathus is recovered as sister group of Areoda (Jameson 1990), sharing as common characters the presence of the mesoventral process and asymmetrical parameres, and the same geographic distribution (MacLeay 1819; Ratcliffe & Jameson 1989). They differ in colour, size, clypeal shape (Ratcliffe & Jameson 1989), and in paramere shape: in Areoda, the lateral processes are hooks, whereas they are lobes in Oplognathus. Oplognathus bears three distinct teeth on the mandibles; Areoda bears two teeth.
Characters such as the shape of the last labial palpomere, the depth of elytral striae, and the shape of parameres (commonly used as diagnostic characters in other genera within Scarabaeoidea Latreille, 1802, including Areoda) are not useful to separate species of Oplognathus, where these structures often vary within species. On the other hand, the characteristics of the mouthparts (such as mandible shape, the last maxillary palpomere, and mentum shape) are important for the species identification.
Despite being a genus with few species, many nomenclatural problems were encountered (detailed in the section 'nomenclatural history'), in addition to the lost type of Oplognathus kirbii. The type specimen of O. kirbii was not found in the MacLeay Museum (MMUS), nor in the Natural History Museum London (NHMUK), where the MacLeay collection is housed. Ratcliffe & Jameson (1989) reported that George Masters, curator of the MacLeay Museum collection from 1872 to 1912, relabelled many specimens and destroyed the original labels. However, all the examined specimens identified as O. kirbii were conspecific, in addition to an illustration of Guérin-Méneville (1844: pl. 24 bis fig. 10). Therefore, we designate a neotype to stabilize the classification of the genus and species. This genus can be considered rare, due to the few specimens in collections. In most cases, the specimens are very old, with no precise data and there are almost no recent records. Oplognathus kirbii is the most present species in collections, quite possibly because the localities where it occurs were more sampled in the past.