﻿Revision of the genus Atholus Thomson, 1859 (Coleoptera, Histeridae, Histerinae) from the Philippines with additional records

﻿Abstract The Philippine species of the genus Atholus Thomson, 1859 are revised and re-examined based on museum as well as freshly collected specimens. Atholustorquatus (Marseul, 1854) is re-described, and SEM micrographs and illustrations of both male and female genitalia are provided. Atholusbakeri (Bickhardt, 1914) and Atholusnitidissimus Desbordes, 1925 are also re-described based on images of syntypes. Atholuspirithous (Marseul, 1873) and A.torquatus (Marseul, 1854) are new to the Philippine archipelago. Atholuscoelestis (Marseul, 1857) and A.philippinensis (Marseul, 1854) are provided with diagnostic descriptions and images. A key to the Philippine species is provided.


Introduction
Atholus Thomson, 1859 is a cosmopolitan genus of Histerinae: Histerini (Coleoptera: Histeridae) spread across the world, with the exception of the Continental Australia and Antarctica. The genus contains 77 described species hitherto; almost half of them occur in the Oriental Region (Mazur 2011).
Philippine Atholus have received only limited attention, and in the recent worldwide catalogue of Histeridae (Mazur 2011), only two species -A. nitidissimus Desbordes, 1925 and A. bakeri (Bickhardt, 1914) from the archipelago were reported as Philippine endemics. Few species were indicated generally in the catalogue to occur in the Oriental region, such as Atholus coelestis (Marseul, 1857); Mazur et al. (2015), however, reported this species from Luzon Island.

Materials and methods
Fresh specimens were collected by the senior author under ruminant dung and decaying banana stumps. All museum specimens were loaned from the following institutes: the Hokkaido University Museum, Sapporo (SEHU; M. Ôhara), except the syntypes from Muséum National d'Histoire Naturelle, Paris, France (MNHN; A. Mantilleri) and Naturhistorisches Museum Berlin, Germany (MNHUB; B. Jäger). General observations and dissections were carried out under stereomicroscopes Nikon SMZ745T and Nikon SMZ800. Detailed observations of several structures were performed using SEM (JEOL JSM-6510). Genitalia were dissected and treated according to methods of Ôhara (1994). In this paper, we treat the number of denticles of both apical and outer lateral margins of protibia combined as the 'outer margin', and denticles along the outer lateral margin as the denticles on 'outer sublateral margin', and compare it with the result of Ôhara (1992, 1993). Body measurements are as follows: PEL (length between anterior angles of pronotum and apices of elytra), APW (width between anterior angles of pronotum), PPW (width between posterior angles of pronotum), EL (length of elytron along sutural line), and EW (maximal width between outer margins of elytra). General morphological terminology follows Ôhara (1994) and Lackner (2010). Regarding syntypes of A. nitidissimus Desbordes, 1925 and A. bakeri (Bickhardt, 1914), only images of syntypes were available. Hister sectator Lewis, 1901: 375, synonymized by Bickhardt, 1917 Atholus sectator : Lewis 1906: 402. Atholus philippinensis: Lewis 19061915: 55;Mazur 1984: 215;1997: 132;2011: 106 [catalogued] (Marseul, 1854) (Fig. 1) is easily distinguished from other Philippine congeners by entire dorsal elytral striae 1-3 (fourth stria is incomplete), and dense punctation of propygidium and pygidium. Among Philippine species, it is the largest one in size, with its markedly wider elytra and posterior angles of pronotum. The number of denticles of the outer sublateral margin of protibia is four.
Additional description. Female genitalia: anterior portion of valvifers (Figs 35, 36) paddle-shaped; gonocoxite ( Fig. 37) slightly elongate, almost twice as long as broad, shovel-like; inner and outer surfaces differentiated; inner face moderately separated from outer face by elevated lateral ridge; sclerotized setae on apical half of outer face short and somewhat dense; inner face with short and sparse setae; apex of gonocoxite with two teeth; gonostyli present, freely articulated; spermathecae multiple, consisting of four sacs; sacs gradually enlarged and elongate, not sclerotized.
Biology. This species occurs in decaying banana stumps and are often found along with some species of Platylister (Platysomatini, Histerinae, Histeridae).
Remarks. The protibial teeth of A. philippinensis (Marseul, 1854) are not as prominent as they are in other species. Moreover, in comparison to the description of Ôhara (1999b), the number of denticles may vary, ranging from 9-11 on the outer margin, one on the inner apical angle, and four or five on the outer sublateral margin. This species was already re-described based on specimens of Taiwan and western Kalimantan, Indonesia (Ôhara, 1999b), including the illustrations of male genitalia and spermatheca of female. Ôhara (1999b) also provided a figure of the spermatheca; we add illustrations of the female gonocoxite and valvifers here  Atholus coelestis: Lewis 1906: 402;1915: 55 [Formosa=Taiwan];Mazur 1984: 212;1997: 129;2011: 104 [catalogued]; Mazur et al. 2015: 1454; Ôhara, 1992: 173-176;1994: 137;1999: 110 [Nansei Islands];1999b: 31-32 [Taiwan]. Atholus (Euatholus) coelestis: Hisamatsu and Kusui 1984: 17 [noted, key]. Atholus (Euatholus) coelestes [sic] : Hisamatsu 1985: 228, pl. 41, f. 61 [noted, key, image]. Diagnosis. Atholus coelestis (Marseul, 1857) is best characterized by its third dorsal elytral stria extending inwardly towards the apical end of the fourth and fifth striae. The slight emargination on the anterior margin of the mesoventrite is also a distinct character of this species. The number of denticles of the protibia (Figs 13,14), is 11 on the outer margin, one one the inner apical angle, and eight on the outer sublateral margin. The protibial teeth are slightly prominent only on the outer apical angle, topped with three denticles. The number of denticles on the outer margin may range from 11-13 denticles. The shape of the gonocoxite of A. coelestis (Marseul, 1857) is slenderer, becoming narrower towards the apex compared to A. philippinensis (Marseul, 1854). Moreover, the presence of a single occipital fovea on the posterior portion of the head of A. coelestis (Marseul, 1857) (Fig. 11) is rather a remarkable character differentiating it from other species that has not been previously described.
Additional description. Female genitalia: anterior portion of valvifers (Figs 38, 39) paddle-shaped; gonocoxite ( Fig. 40) elongate, almost 4× as long as broad, not shovel-like, more narrowed on apical end; inner and outer surfaces differentiated; inner face weakly separated from outer face by elevated lateral ridge; sclerotized setae on apical half of outer face short and sparse; inner face with short setae and moderate setae; apex of gonocoxite with two teeth; gonostyli present, freely articulated; spermathecae multiple, consisting of four sacs; sacs gradually enlarged and elongate, not sclerotized.
Distribution. Widely distributed in the Oriental Region including China, Taiwan, Ryukyu Islands (Japan). Also present in the Palearctic Region: Tajikistan and in the Afrotropical Region: Comoros Islands (Mazur 2011).
Biology. All individuals of A. coelestis (Marseul, 1857) were collected from dungs of cows and water buffaloes of lowland farms and pastures across all islands of the archipelago. This species may also seem to be moisture-specific, as they were observed to dwell only on more desiccated dungs during field collection.
Remarks. Atholus coelestis (Marseul, 1857) (Fig. 2) is a widespread species across the Philippine archipelago showing a consistent morphology in all individuals examined. Atholus coelestis (Marseul, 1857) was re-described by Ôhara (1992) (Marseul, 1854) is recognized with a combination of its interrupted lateral pronotal stria in the anterolateral angle, and fine punctations on the apical portion of its pygidium. This species also possesses remarkable teeth of protibia, increasing in size apically. The structure of the female genitalia of this species is described here for the first time, showing its similarity to the shape of the gonocoxite of A. philippinensis (Marseul, 1854), which is broad and shovel-like.
Pronotum: marginal pronotal stria laterally complete, continuous onto apical angle and behind head; lateral pronotal stria (Fig. 19) deeply impressed, slightly crenate and complete; lateral stria rather distant from margin, its basal end abbreviated to basal fourth of pronotal length; apical end bent inwardly behind apical angle; anterior pronotal stria absent; disk with sparse microscopic punctures, wholly covered with alutaceous microsculpture; area behind apical angles bare; posterior margin without row of coarse punctures; ante-scutellar region with a single short longitudinal puncture.
Prosternum: prosternal lobe with anterior margin (Fig. 23) round; medio-apical end of prosternal lobe ascending; marginal prosternal stria deeply impressed, carinate and shortly interrupted medially; short striae present on both baso-lateral corners; lobe with few setiferous coarse punctures inside and outside of marginal stria on both sides,     separated by their 1-2× their diameter; disk covered with sparse, finer punctures on apical half; prosternal suture lightly impressed; prosternal process covered with few, setiferous fine punctures; lateral sides descending; lateral prosternal striae deeply impressed and complete; lateral disk with several coarse setiferous punctures; basal half narrow; posterior margin of basal lobe strongly emarginated.
Meso-and metaventrite: anterior margin of mesoventrite outwardly arcuate (Fig. 24); marginal mesoventral stria complete, carinate, sparsely crenate; stria behind anterolateral angle present; mesoventral disk sparsely clothed with fine punctures separated by 4-5× their diameter; meso-metaventral suture clearly impressed, complete and medially angulate; lateral metaventral stria deeply impressed, carinate, extending obliquely and posteriorly, united with oblique stria which inwardly extends from basal third of metaventro-metepisternal suture; post-mesocoxal stria extending posteriorly and strongly curved along posterior mesocoxal margin, almost attaining metaventro-mesepimeral suture; punctures of metaventral disk similar to those of mesoventrite; a row of coarse punctures present along inside lateral metaventral stria; longitudinal suture of metaventrite lightly impressed; lateral disk of metaventrite moderately covered with setiferous large round and shallow punctures; interspaces with sparse, coarse to fine punctations; mesepimeron, metepimeron and lateral disk of first abdominal ventrite with dense setiferous, large punctures; interspaces with few coarse to fine punctations; metepisternum with sparse punctures on apical half; punctation of intercoxal disk of first abdominal ventrite similar to that of metaventrite; lateral stria deeply impressed, slightly carinate and complete.
Legs: anterior face of protibia (Fig. 27) flattened, dilated and clothed with few, fine ocelloid punctures; basal to median area with weak strigate sculpture; outer lateral margin with four teeth, becoming stronger apically; topped by minute denticles; protarsal groove shallow, with few coarse punctures; anterior protibial stria lightly impressed; inner marginal stria present on basal half, along stria a slightly depressed with row of coarse punctures present; near tarsal insertion with two spine-like tarsal denticles; another one, more distant and longer, located at inner anterior angle; protibial spur moderately long, wider on basal margin, approximately half the length of protarsus; posterior face of protibia ( Fig. 28) with sparse, fine punctures and strigate ground sculpture from basal to median surface; number of denticles on outer margin eight, one on inner apical angle, outer sublateral margin three or four; median posterior stria moderately impressed and abbreviated on apical end; inner posterior stria moderately impressed with row of sclerotized setae, terminating in three inner posterior denticles; inner margin of setae present on apical half, with a row of short setae on basal half; inner margin with strigate ground sculpture; profemur sparsely clothed with fine, ocelloid punctations; surface with lightly strigate ground sculpture; marginal stria complete; anterior stria present on apical half; femoral stria almost complete, shortened on basal end; posterior margin with large punctations; a row of setae present on both basal and apical ends.
Anterior portion of valvifers (Figs 41, 42) paddle-shaped; gonocoxite (Fig 43) slightly elongate, almost as twice as long as broad, shovel-like; inner and outer surfaces differentiated; inner face moderately separated from outer face by elevated lateral ridge; sclerotized setae on apical half of outer face short and slightly dense; inner face with short and sparse setae; apex of gonocoxite with two teeth; gonostyli present, freely articulated; spermathecae multiple, consisting of four sacs; sacs gradually enlarged and elongate, not sclerotized.
Biology. Atholus torquatus (Marseul, 1854) were collected within the dung of cows located in a higher elevation and semi-forested area. The substrate also differs from A. coelestis (Marseul, 1857), as A. torquatus (Marseul, 1854) was typically observed in soggy, moist dung. (Marseul, 1854) is a quite variable species regarding the external subhumeral stria on its elytra, either clearly marked or totally absent. This character is also mentioned by Desbordes (1917) who mentions the stria can be aberrant. Although the type specimen of A. torquatus (Marseul, 1854) according to the original description possesses no external subhumeral stria, we have examined one specimen with the subhumeral stria present. This corresponds to Desbordes' (1917) observation. Our observations confirm the variability of this character among specimens ranging across Continental as well as Insular Southeast Asia. On the other hand, male and female genitalia exhibit little variation. We therefore propose to drop the external subhumeral stria as the primary key character for delimiting this species from others.
Biology. Unknown. Remarks. All seven examined individuals of Atholus pirithous (Marseul, 1873) (Fig.  4) lack internal subhumeral stria, but traces of dots and short lines can be observed in the apical end. The outer apical protibial tooth of this species is moderately prominent, topped by three denticles. The total number of protibial denticles on the outer margin is ten, one on the inner apical angle (Figs 48, 49), compared with the Japanese specimens described that bore only nine denticles (Ôhara, 1993), but the outer sublateral margin of the Philippine species has only four denticles; when compared to Ôhara (1993) who observed five to six denticles. Moreover, all examined specimens lost their genitalia prior to examination. Desbordes, 1925 Figs 5, 50-53 Atholus nitidissimus Desbordes, 1925: 87 [Leyte Island]; Mazur 1984: 215;1997: 131;2011: 105 [catalogued].

Atholus nitidissimus
Specimens examined. Two syntypes of undetermined sex housed in MNHN have been examined by N. Dégallier. The following re-description is based on images provided by him.
Diagnosis. This species is easily distinguished by its almost circular body and absence of sutural elytral striae. Judging by the images of two examined syntypes, this species is clearly distinct in its pattern of dorsal elytral striation, differing from other species by the absence of the fifth or sutural elytral striae. Atholus nitidissimus Desbordes, 1925 (Fig. 5) is similar to A. coelestis (Fig. 2), albeit it is comparatively smaller in size than other species examined.
Pronotum: marginal pronotal stria (Fig. 50) laterally complete, continuous onto the apical angle and behind head; lateral pronotal stria moderately impressed; apical end shortened and bent inwardly; lateral portion rather distant from margin; its basal end obsolete on basal sixth of pronotal length.
Pronotum: marginal pronotal stria (Figs 54, 55) laterally complete, continuous onto apical angle and crenate behind head; lateral pronotal stria moderately impressed, slightly crenate; apical end shortened and bent inwardly in a curved hook; lateral portion rather distant from margin; its basal end abbreviated from basal fifth of pronotal length.
Legs: posterior surface of protibia (Fig. 57) flattened and strongly dilated; outer lateral margin with four weak, almost inconspicuous teeth, topped by minute denticles.

Biology. Unknown.
Remarks. The examined syntype of A. bakeri (Bickhardt, 1914) exhibits characters similar to a typical A. torquatus (Marseul, 1854). According to Desbordes (1917), A. torquatus (Marseul, 1854) and A. bakeri (Bickhardt, 1914) are very similar, being set apart by the pygidial punctation (strong in A. bakeri and apically finer in A. torquatus). Although the only examined specimen of A. bakeri (Bickhardt, 1914) possesses similar pygidial punctations to A. torquatus (Bickhardt, 1914), this character remains the primary distinction until further examinations of other types is established. The authors would also encourage a comprehensive observation of both male and female genitalia for future works.

Discussion
Structures of the protibia in almost all Oriental species of Atholus were not described in detail in the original descriptions, particularly regarding the number and localization of denticles of protibia. In the previous works of Ôhara (1992, 1993, 1999b), the occurrence of denticles on designated margins such as lateral outer margin, anterior margin, and apical angle were described. However, since the protibial teeth of some Atholus species are not as strong as in others, it seems that the denticles on the apical angle may be ambiguously considered as denticles of either the apical margin, or of the outer lateral margin.
The gonocoxites of A. philippinensis (Marseul, 1854) and A. torquatus (Marseul, 1854) are relatively similar in their forms, appearing to be shovel-like in shape. We have observed this similarity with the gonocoxite of Atholus bifrons (Marseul, 1854) (dela Cruz and Ôhara 2022) from Ryukyus (Japan) and Borneo (Indonesia). On the other hand, the shape of the gonocoxite of A. coelestis (Marseul, 1857) is narrow and cone-like and becoming slenderer apically. Nevertheless, the number of spermathecal sacs (four) of A. philippinensis (Marseul, 1854), A. coelestis (Marseul, 1857), A. torquatus (Marseul, 1854), and even A. bifrons (Marseul, 1854) (dela Cruz and Ôhara 2022) is consistent among these species. Although we have not included this structure in the taxonomic key, since the female genitalia of other species examined were not available, the gonocoxite of Atholus might also become a useful tool for morphological diagnosis in the future.
Atholus species are generally widespread throughout the Oriental Region. A few species appear to be endemic to some regions such as A. nitidissimus Desbordes, 1925, only recorded so far from the island of Leyte in the Philippines, and A. bakeri (Bickhardt, 1914), reported only from Luzon Island hitherto. In this study, A. coelestis (Marseul, 1857) is revealed to be a ubiquitous species, spread across the islands of the Philippine archipelago. Atholus pirithous (Marseul, 1873) and A. torquatus (Marseul, 1854) are new records for Philippines. We examined six species of Philippine Atholus in this work; yet, we expect the number to rise in the future since the archipelago is situated in the vicinity of the Greater Sunda Islands in the Indonesian archipelago. It is therefore plausible that other species occurring there might also occur in the Philippines.