Taxonomic revision of the Canthidium Erichson, 1847 species of the gigas group (Coleoptera, Scarabaeidae, Scarabaeinae)

. The gigas species group of the subgenus Canthidium ( Neocanthidium ) is de ﬁ ned and described. This species group is composed of three described species [ C. gigas Balthasar, 1939, Brazilian Atlantic Forest, including intrusions into Cerrado, C. bokermanni (Martínez et al. , 1964), Chaco and western Cerrado in Brazil, Bolivia, Paraguay, and Argentina, and C. kelleri (Martínez et al. , 1964), Brazilian Cerrado and neighbouring open areas] and three new species: Canthidium stofeli sp. nov. from the western and southern regions of the Brazilian Amazon, Canthidium feeri sp. nov. from French Guiana, and Canthidium ayri sp. nov. from the Brazilian Atlantic Forest. We present descriptions and redescriptions, illustrations, an identi ﬁ cation key and comments on the distributions of the species of the gigas group.


Introduction
The genus Canthidium Erichson, 1847 is diagnosed by the presence of nine-articulated antennae with a pubescent club; cylindrical labial palpi; ventral clypeal process usually absent, if present in the form of one longitudinal carina; mesoventrite very short; metaventrite usually simply convex; and dilation of meso and metatibia with a curved inner margin and an more or less straight outer margin in ventral view (Vaz-de-Mello et al. 2011).Canthidium is currently subdivided into two subgenera, Canthidium s. str.and Neocanthidium Martínez & Halffter, 1986, with some species not presently assigned to any subgenus (see Cupello 2018).

Institutional abbreviations
A total of 129 specimens were examined from the following collections: Pictures were taken using a Leica M205C stereo microscope and the images were stacked with the manufacturer's software.Maps were generated with Diva-Gis (ver.7.5.0),using the shapefi le of Löwenberg-Neto (2014) of the biogeographical regionalization of Morrone (2014).Holotype label data were transcribed verbatim in quotation marks; text lines are separated by a slash mark.The nomenclature used for the geographical distributions is based on the biogeographical regionalization scheme of Morrone (2014) .The nomenclature used for the microsculpture is based on Harris (1979).
Specimen lengths were measured from the mid-anterior part of the pronotum to the elytral apex to eliminate potential errors caused by various inclinations of the head; therefore, the length provided here is just a 'partial length', not the total length of the specimens.

Diagnosis
Species of the gigas group are readily recognizable from other members of the genus by their large (8 to 15 mm), globose black body, which contrasts with the light-coloured antennae.In addition, the group shows coarse punctation on head and anterior surface of the pronotum; dorsal surface of the eyes posteriorly narrowed; interocular distance approximately seven times wider than the maximum dorsal eye width, and clypeus with two well-defi ned rounded teeth separated by an acute angle.

Description
Clypeal margin well defi ned internally, with two more or less rounded teeth medially, separated by an acute angle.Clypeogenal suture distinct.Hypomeron with coarse longitudinal microsculpture between punctuation and obliquely-oriented setae.Prosternum with few long setae, with greater concentration at central region, the apex of each setae reaches mesoventrite.Profemora with ventral surface with a longitudinal carina along posterior margin and with a distinct row of punctures along anterior margin, each puncture with a golden seta; surface with microstriae; tibiofemoral joint with a tuft of golden setae.Protibiae widening towards apex, external edge with three teeth, external edge serrate between proximal tooth and base, dorsal surface with punctation along the central axis, anteriorly with long setae; venter with longitudinal carina and a single row of punctures parallel to lateral edge.Protibial spur tapering towards apex and more or less angulate at apical third in females or wider apically and bent ventrally at median half in males.Tarsi with fi ve tarsomeres; claws simple, strongly curved.Mesofemora with a carina along posterior edge, ventral surface with some setae anteroapically, centre and apex with minute punctation.Mesotibiae with narrow basal half, apical half abruptly dilated, with carina and punctation along anterior margin, near the carina with punctation; external edge with small teeth, internal edge smooth.First mesotarsomere as long as next two mesotarsomeres combined; second to fourth mesotarsomeres decreasing gradually in length and fi fth mesotarsomere longer than the fourth; claws simple and strongly curved; two apical spurs, one as long as the fi rst mesotarsomere and the other as long as the fi rst and second mesotarsomeres combined.Elytral striae wide and distinct, with circular punctures slightly wider than the striae.Interstriae with small, scattered punctures.Pseudepipleuron narrowing gradually towards the apex, where it dilates slightly at the end of the fi fth striae; surface with sparse fi ne punctation.Abdomen glabrous, fi nely punctate.Pygidium convex, margined along posterior edge, distinctly punctate.

Sexual dimorphism
Males and females can be differentiated by the protibial spur, which has a narrow apex in females and is fl attened in males.-Frontoclypeal carina with length greater than four-fi fths of interocular width.Pronotum with both anterior carina and two lobes sharply evident, separated from border by a distance equal or greater than the latter's width; disc with surface completely punctate (Fig. 1C).Amazon rainforest south of the Amazon River in Brazil and Peru ..  (Martínez et al., 1964)

Diagnosis
Canthidium ayri sp.nov. is differentiated from the other species in the group by the unarmed head and pronotum, lacking projections.

Etymology
Named for Ayr de Moura Bello, great collector and enthusiast of Brazilian beetles, directly or indirectly responsible for the present increase of studies on Brazilian Coleoptera.HIND LEG.Metafemora with a carina along posterior edge, anterior edge with setal fringe, surface with fi ne punctation.Metatibiae elongated and gradually dilated towards the apex; external margin serrated.

Holotype
AEDEAGUS.In dorsal view, parameres with median angulation nearly absent and with a shallow apical cavity; in lateral view, with dorsal angulation at the basal one-third.

Variation and sexual dimorphism
Length ranging from 8.00 to 8.31 mm.Males with ventrite VI wider medially, female ventrite VI with the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Diagnosis
Canthidium kelleri differs from other species of the gigas group by the presence of a conical projection on the head which varies in development according to the size of the specimen.HIND LEG.Metafemora with a carina along posterior edge, anterior edge with setal fringe, surface with fi ne punctuation.Metatibiae elongated and gradually dilated towards the apex; external margin serrated.

Variation and sexual dimorphism
Length ranging from 8.95 to 11.54 mm.Smaller specimens have the frontal horn reduced in size, appearing as a transverse gibbosity.Pronotum with the anteromedial depression less visible and shallower in some specimens.Pygidium slightly less convex if compared with C. bokermanni.Males present a small tooth in the upper ventral part of their metatibiae.Males with ventrite VI wider medially, female ventrite VI with the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Geographical distribution
The specimens examined were collected in Paraguay (Cordillera) and Brazil (Mato Grosso, Mato Grosso do Sul, Goiás, Distrito Federal and Minas Gerais).It is present in the Cerrado and the Chaco biomes, which lie in the Chacoan dominion.

Comments
The holotype and one paratype originally identifi ed as male of D. paraguayanus were examined by us and were shown to be C. kelleri, thus confi rming the name's synonymy with C. kelleri as fi rstly proposed by Nunes & Vaz-de-Mello (2013).However, two paratypes originally said to be females by Gandini & Aguilar (2009)

Description (holotype)
MEASUREMENTS.Length: 9 mm.HEAD.Surface dense and distinctly punctated.Frontoclypeal carina rectangular and with length less than three-fourths of interocular distance.
PRONOTUM.With anterior carina and lobes not evident, positioned just behind anterior border and separated from border by distance less than the border width; anterior region of disc punctated, posterior region with indefi nite punctation.
METAVENTRITE.With simple and shallow punctation, laterobasal and lateral region with microsculpture fi nely strigulate.MESEPIMERON AND MESEPISTERNUM.With shallow punctation and microsculpture fi nely strigulate.HIND LEG.Metafemora with a carina along posterior edge, anterior edge with setal fringe, surface with fi ne punctation.Metatibiae elongated and gradually dilated towards the apex; external margin serrated.

Variation and sexual dimorphism
Total length ranging from 9.00 to 10.67 mm.Some males present a small tooth in the upper ventral part of their metatibiae and some have a protuberance on their basal half.Males with ventrite VI wider medially, female ventrite VI with the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Geographical distribution
All the specimens examined for this work were collected in French Guiana, which is located in the Boreal Brazilian dominion.

Description (holotype)
MEASUREMENTS.Length: 10 mm.HIND LEG.Metafemora with a carina along posterior edge, anterior edge with setal fringe, surface with fi ne punctation.Metatibiae elongated and gradually dilated towards the apex; external margin serrated.
AEDEAGUS.In dorsal view, parameres with a strong concave angulation and abruptly curved apex.

Variation and sexual dimorphism
Length ranging from 8.87 to 11.11 mm.The projections on the pronotal disc vary according to the size of the specimen, being allometrically developed as the size of the body increases.Males with ventrite VI wider medially, female ventrite VI with the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Geographic distribution
The specimens examined came from Brazil (Mato Grosso, Rondônia, Pará) and Peru (Madre de Dios).The species occurs in the southern region of the Amazon biome, corresponding to the Southeastern Amazonian dominion and Boreal Brazilian dominion.Balthasar, 1939  of 120°.In C. bokermanni, in dorsal view, the apical angulation is almost absent and there is a shallow medial excavation at the apex; in lateral view, the parameres have a dorsal internal angulation of 160°.

Type locality
Brazilian Atlantic Forest.Originally said to be Cayenne, French Guiana, but this is an error.See geographic distribution below.

Redescription
HEAD.Surface with dense and distinct punctation, particularly on clypeus.With a transverse raised projection in the front.
PRONOTUM.Without anteromedial depression, disc anteriorly convex, sometimes with an anterior sinuosity forming two broad and shallow depressions (both surrounding the medial line).Surface with dense and distinct punctation, attenuating towards the centre of disc, where punctation is fi ne and sparse.HIND LEG.Metafemora with a carina along posterior edge, anterior edge with setal fringe, surface with fi ne punctation.Metatibiae elongated and gradually dilated towards the apex presenting a sinuosity; external margin serrated.
AEDEAGUS.In dorsal view, parameres with a strong angulation in apical half and with a concave excavation from the middle to the apex; in lateral view, with internal medial angulation of 120° dorsally.

Variations and sexual dimorphism
Length ranging from 9.40 to 12.65 mm.Transverse projection of head sometimes not well defi ned.The males have a tooth in the upper ventral part, more developed in some specimens than in others.Males with ventrite VI wider medially, female ventrite VI of the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Geographical distribution
The specimens examined were mostly collected in the Brazilian states of Minas Gerais, São Paulo, Espírito Santo and Paraná in the Atlantic rainforest biome, located in the Paraná dominion.The record from Distrito Federal is surprising for the species.Judging from the rest of the known distribution, its presence there may be due to gallery forest connecting it to the Atlantic Forest on the coast.Although the holotype is labelled as coming from French Guiana, we believe this represents a mislabelling, since Fig. 10.Geographical distribution of Canthidium gigas Balthasar, 1939 (circles) and Canthidium bokermanni (Martínez et al., 1964) (triangles).. no other specimens have been reported from that region.Furthermore, the German entomologist Carl Felsche (who acquired the specimen) was known for buying insects, and this kind of mislabelling has been seen before with his specimens (FZVM, personal observation).

Variation and sexual dimorphism
Total length ranges from 9 to 13 mm.The transverse carina of the head varies from rectangular to oval, regardless of the size and sex of the specimen.The males have a tooth in the upper ventral part, more developed in some specimens than in others.Males have ventrite VI wider medially, female ventrite VI is of the same length throughout.Males also have protibial spur fl attened, while in females the protibial spur is narrowed and pointed.

Geographical distribution
The specimens examined were collected in Argentina (Chaco), Brazil (Mato Grosso and Mato Grosso do Sul), Bolivia (Santa Cruz), and Paraguay (Concepción and Boquerón).The species occurs in two different biogeographic dominions: the Chacoan dominion and the South Brazilian dominion.

Comments
Two paratypes of Dichotomius paraguayanus, which were incorrectly interpreted as females by Gandini & Aguilar (2009), proved to be males and to belong to C. bokermanni.
In addition to the above described morphological characteristics that separate the species, the group is well established based on its geographical distribution.Endemic to South America, the species occurs in different ecoregions.Canthidium gigas and C. ayri sp.nov.are endemic to the Atlantic Forest, their occurrence being restricted respectively to the north and south of this biome.Canthidium bokermanni and C. kelleri are found in Cerrado vegetation; C. bokermanni in the west region of the biome, and C. kelleri in the east.Finally, C. feeri sp.nov. is restricted to French Guiana, north of the Amazon biome, and C. stofeli sp.nov.occurs in the southern region of this biome.
The group also has unique characteristics regarding feeding.Most species of Scarabaeinae are coprophagous, but there may be variations, such as C. kelleri and C. bokermanni feeding on the mycelia of fungi (Halffter & Matthews 1966).Most recently, Falqueto et al. (2005) reported C. gigas from fungus-baited pitfall traps.The two paratypes of C. ayri sp.nov.were collected with light traps and the other species often appear in fl ight interception traps, in addition to traps baited with fungi.More studies and fi eld observations are needed to confi rm if fungi are indeed a fundamental part of these species' diet.

Conclusions
This work dealt with the taxonomic revision of the Canthidium species of the gigas group.We described three new species for the group, but we fi rmly believe that in order to broaden the distribution data more studies are required, including fi eld collecting and museum studies.
HEAD.Surface densely and distinctly punctated; with rectangular frontoclypeal carina, length greater than four-fi fths of the interocular distance.PRONOTUM.Completely punctate, with dense and distinct punctation, becoming more accentuated towards the centre of the disc, regularly convex with two medial projections anteriorly, one on each side.HYPOMERON.Hypomeral carina slightly curved toward edge.
HYPOMERON.With microstriae and setae in the basal part.Hypomeral carina complete curved throughout its length.METAVENTRITE.With simple and shallow punctation, laterobasal region with stronger punctation, lateral region with microsculpture obscurely variolate, almost semicircular.
DiagnosisCanthidium feeri sp.nov.differsfromother species of the group by the distinct anterior pronotal punctation, apparently lacking punctures on the centre of the disc.EtymologyNamed for François Feer, French scarabaeidologist, working at the Muséum national d'Histoire naturelle (Paris, France) who collected half of the type series.
DiagnosisCanthidium stofeli sp.nov.differs from the other species in the group by having two anterior medial projections, one on each side of the pronotum.
EtymologyNamed after Roberto Stofel, for the fi eld support during collections in Cotriguaçu.