Parachorius semsanganus sp. n. (Coleoptera, Scarabaeidae, Scarabaeinae) from Laos and its significance in the phylogeny of Oriental Deltochilini

Abstract The new species Parachorius semsanganus sp. n. is described from Laos. This enigmatic Oriental deltochiline represents a “morphological link” between Parachorius and Cassolus by sharing characters of the two genera. The fact that Parachorius semsanganus cannot be unequivocally placed in either of these two genera stresses some more general problems of the current classification of Parachorius and Cassolus. Such problems can be solved only in the course of phylogenetic analysis, the need of which is briefly outlined.


introduction
The dung beetle tribe Deltochilini Lacordaire, 1856 (= Canthonini Lansberge, 1874, synonymy according to Bouchard et al. (2011)), displays a Gondwanian distribution and is the most genus-rich tribe of the Scarabaeinae. It comprises 873 species grouped into 91 genera that constitute 40% of the entire generic diversity of the subfamily Scarabaeinae (Davis et al. 2008). However, the monophyly of the tribe is doubtful according to a revision of African genera (Scholtz and Howden 1987), and it appears polyphyletic in the morphology-based and molecular phylogenies (Philips et al. 2004;Ocampo and Hawks 2006;Monaghan et al. 2007;Sole and Scholtz 2010). Such ambiguity highly complicates the diagnosis of the tribe and thus makes a consensus about its generic composition impossible at the moment.
The Oriental genus Parachorius Harold, 1873 comprises six species and, according to the last monographic study (Balthasar 1963), belongs to the tribe Pinotini Kolbe, 1905, which is a synonym of the Ateuchini Laporte, 1840 (Smith 2006;Bouchard et al. 2011). Vaz-de-Mello (20072008) places Parachorius within the tribe Coprini Leach, 1815 based on morphological phylogenetic analysis of Ateuchini and related taxa. By contrast, another preliminary morphology-based phylogeny of Oriental Deltochilini using aedeagal and somatic characters (Tarasov, unpublished) strongly suggests that Canthon Hoffmannsegg, 1817 (the most speciose genus of the Deltochilini), Parachorius, and another Oriental deltochiline genus Cassolus Sharp, 1875, form a monophyletic group. Therefore, here, we treat Parachorius as a deltochiline. Based on study of external morphological characters within the tribe Deltochilini, Parachorius seems to be most closely related to the genus Cassolus. The genus Cassolus includes nine species that are morphologically very heterogeneous. Such morphological variation, especially when compared with the morphology of the known species of Parachorius, may indicate a nested position of the latter genus within Cassolus (Tarasov, unpublished).
Whilst surveying recent scarab collections from Laos deposited at the Naturhistorisches Museum in Basel, Switzerland (NHMB), we discovered a very interesting deltochiline species displaying a mixed character set between Parachorius and Cassolus. This species cannot be unequivocally placed in either genus using current taxonomic concepts of these taxa (Balthasar 1963). However, we tentatively place this new species in the genus Parachorius.
Discovery of this species supports the above mentioned evidence for the close relationship between Cassolus and Parachorius as well as our provisory placement of Parachorius within the Deltochilini. Its description, provided here, enables its incorporation in the upcoming phylogenetic analysis of the entire generic complex.

Material and methods
All photos were taken with a digital camera attached to a dissecting microscope (Leica MZ16A). Male aedeagi in Figs 1-3 were photographed in glycerin. First, the dissected aedeagus was macerated in 10% solution of KOH for several hours and then rinsed with distilled water. Finally, the aedeagus was placed in glycerin for taking pictures and subsequent storage.
All the material used in this study is housed in the NHMB.

Species description
Parachorius semsanganus Tarasov  Description. Oval, convex, black, entirely shiny; mouthparts, antennae and legs red-brown. Dorsal body side covered with two types of punctures: larger (normal) punctures and very tiny punctures (which can be observed only under higher magnification of 40x or more) Dorsal and ventral body sides glabrous. Length 8.2-10.6 Male (Fig. 4). Head flat, punctation fine; anterior margin notched medially; notch delimited by 2 prominent triangular obtuse teeth; clypeus laterad of each tooth very slightly notched; eyes completely divided by canthus into lower and upper lobes; lower lobes significantly larger than upper ones; genae and clypeus not distinctly separated from frons; genae rounded and protruding; antennae with 9 segments, antennal club with 3 segments.
Protibiae with three outer teeth; 1st tooth slightly thicker than two others; inner margin with two vertical teeth underneath, located approximately opposite to 2nd and 3rd outer teeth; protibial apical spur acute, long, reaching middle or apical portion of 3rd tarsal segment; sometimes protibial teeth and apical spur abraded.
Female. Similar to male but with the 1st protibial outer tooth slightly thinner than in males; metafemoral posterior margin not serrate; metatibial inner margin not denticulate.
Variation. All specimens of the type series look very similar to each other. Some variation may be observed in the shape of teeth on the metatibial inner margin, which are less expressed in some males due to abrasion.
Holotype (Fig. 4). The holotype specimen lacks the tarsus of the right middle leg. Differential diagnosis. The new species is quite distinct among all other known species of Parachorius and Cassolus. It can be easily separated from them by the following unique set of character states: clypeus near outer side of each clypeal tooth very slightly notched, metatibial inner margin with large teeth (Fig. 5, arrowed), and aedeagus with spatulate apices which are largely bent inward (Figs 1-3).
Distribution and ecology. The species is known from only 16 specimens of the type series collected across a range of altitudes between 1300-1500 m on Phou Sane Mt. of Xieng Khouang province in Laos.
Etymology. The name of the new species is derived from the Latinized Lao words "syam" -link and "sanga" -spectacular. Its meaning "spectacular link" refers to the fact that this species represents a "morphological link" between the genera Parachorius and Cassolus.
Taxonomic notes. Based on taxonomic concepts of the most recent monographic study dealing with Parachorius and Cassolus (Balthasar 1963), the morphological differences between these two taxa can be summarized as follows: Cassolus are normally smaller than Parachorius; the clypeus near the outer side of each clypeal tooth is usually deeply notched in Cassolus and not notched in Parachorius (very slightly notched in P. semsanganus sp. n.); the metatibiae are curved in Cassolus and more or less straight in Parachorius (slightly curved in P. semsanganus sp. n.); some Cassolus species have denticles on the inner metatibial margin, whereas the metatibial margin of Parachorius is not at all denticulate (distinctly denticulate in P. semsanganus sp.n.). As can be seen from this combination of characters, P. semsanganus sp. n. is similar, on the one hand, to Parachorius and on the other hand to Cassolus (in particular to C. gotoi Masumoto, 1986). A robust justification of the taxonomic placement of P. semsanganus sp. n. requires an extensive phylogenetic analysis embracing both Parachorius and Cassolus. Such an analysis is currently in preparation and it may, in particular, result in the synonymy of Parachorius and Cassolus. Therefore to avoid potential nomenclatural changes in the future, we place the new species in the earlier described genus Parachorius.