Taxonomic revision of the South American subgenus Canthon (Peltecanthon) Pereira, 1953 (Coleoptera: Scarabaeidae: Scarabaeinae: Deltochilini)

Canthon (Peltecanthon) is revised in this work. The subgenus now includes four species: C. (P.) staigi (Pereira, 1953), C. (P.) haroldi nom. nov., C. (P.) splendidus Schmidt, 1922 and C. (P.) terciae sp. nov. All species occur in the Atlantic Forest. Maps, natural history information, specimen data and illustrations are provided.

The subgenus Peltecanthon was fi rst described as a full genus and was later reduced to a subgenus of Canthon by Halffter & Martínez (1977). It included the following three described species: Canthon staigi (Pereira, 1953), which is the type species of the subgenus; the so-called 'Canthon sulcatus Perty, 1830', which was placed in the subgenus by Pereira (1953); and Canthon splendidus Schmidt, 1922, which was transferred under the erroneous name of 'Canthon auricollis' by Halffter & Martínez (1977) and later corrected by Vaz-de-Mello & Cupello (2018a).
The last revisions of Peltecanthon were published in the 1970s. Since then, important updates on the morphological delimitation and distribution of the species of Peltecanthon have provided new insights into the taxonomy of this subgenus (e.g., Ferreira-Neto et al. 2017). Currently, it is necessary to establish in an objective and comparative way the characters that differentiate these species, as well as to update the information about their distributions and to correct possible nomenclatural misunderstandings. With access to a new range of material related to these species, our objective was to conduct a taxonomic review of the subgenus Peltecanthon. Lists of examined material were separated into type material and non type material. For type material, labels are transcribed ipsis litteris (text between double quotation marks) and are separated by '/', with species names in italics. After the information from each type label, label colour or main characteristics are briefl y explained in parentheses. In non type material lists, information from labels was organized as follows: country name, in capital letters (e.g., BRAZIL); department or state name in bold letters (e.g., Rio de Janeiro); the number of males (♂ or ♂♂) and females (♀ or ♀♀); municipality and/or locality (when available); coordinates; date (e.g., 3 Mar. 1986); collector (leg.); collection techniques and environmental/ecological information (when available, collection techniques or other details were transcribed in the original language found on the label; text between double quotation marks); and the repository (e.g., CEMT means deposited in CEMT collection).

Material and methods
Morphological analysis and comparisons were conducted using a Leica stereo microscope model EZ 4. The programs Photo Filter and Combine ZP were used for editing of the images. Maps were constructed using Diva Gis, ver. 7.5, while the endophallus structure was drawn using a stereo microscope with a Nikon SMZ 800 camera lucida.

Diagnosis
Among the Scarabaeinae, the tribe Deltochilini features the following characters: hind wing vein radio posterior 1 (RP1) with a small basal appendix and radio anterior 4 (RA4) clearly thinner than RP1 and basally fused with RP1 (Tarasov & Dimitrov 2016). Among the Deltochilini, Canthon (Peltecanthon) can be differentiated by the following combination of characters: shiny pronotum and elytral disc, without tubercles or lateral carinae; ventral surface of the metafemora without anterior margin; and metafemora with elongated base, giving the femur a claviform shape (Halffter & Martínez 1977;Vazde-Mello et al. 2011).

Diagnosis
In the subgenus, Canthon staigi can be distinguished by the following combination of characters. Dorsally elytra and pronotum with blue or green colouration and blue and green refl ections (Fig. 1A). Metafemora with several punctures at base, with no groove (Fig. 1B). Hypomere with thin transverse carina between the anterior and posterior portions, projecting to the median region, anterior region not excavated (Fig. 1C). Propygidium with strong V-shaped carina between pygidium and propygidium (Fig. 1D). Parameres fl attened in lateral view ( Fig. 2A); truncated apex, sub-straight, never sinuous; slightly rounded upper angle; straight lower angle. In dorsal view (Fig. 2B): membranous portion separates the parameres, wider in the central region and narrower at the base and apex. Internal sac ( Fig. 2C-D) with peripheral fronto-lateral sclerite (FLP) involving axial sclerite (A), both structures forming a complex with a central duct, wider at the base, gradually narrowing toward the apex, which is much fi ner; subaxial sclerite (SA) lateral to the FLP + A complex; peripheral medial sclerite (MP) lateral in relation to FLP + A, this with the sharper part passing within a semiduct formed by MP; MP with a central denticle at the inner margin (Fig. 2C); superior right peripheral sclerite (SRP) circular and with semi-circular lateral prolongation.

Remarks
This species was described by Pereira (1953) in the same publication as the description of the subgenus, for which the author simultaneously designated it as the type species.

Distribution
Atlantic Forest, from Pernambuco to Paranaguá, southeast of the state of Paraná. In the literature there are records for Argentina and Paraguay (Pereira & Martínez 1956;Martínez 1959;Halffter & Martínez 1967), but we have not examined any specimens from these localities (Fig. 10). (

Diagnosis
In the subgenus, Canthon haroldi can be separated by the following combination of characters. Elytra and pronotum dorsally green with shades of yellow and red (Fig. 3A). Metafemora with sulcus extending from the base and up to ⅓ of the total femur length (Fig. 3B). Hypomere with no carina between the anterior and posterior portion (Fig. 3C). Propygidium with uniform line between pygidium and propygidium, without any central carina (Fig. 3D). Parameres fl attened in lateral view (Fig. 4A); slightly sinuous apex never strongly sinuous or truncated, with a slight depression near the upper angle; rounded upper angle; lower angle slightly less than 90°. In dorsal view (

Diagnosis
Canthon splendidus can be distinguished by the following combination of characters: elytra and pronotum with different colouration, with pronotum bright with golden or red refl ections, and elytra blue-green (Fig. 5A). In the legs the metafemora with no groove at base (Fig. 5B). Hypomere with a strong excavation in the anterior region, with a thick transverse carina between the anterior and posterior portion projecting to near the lateral margin and never only up to the median region (Fig. 5C). Propygidium with a moderate carina near pygidium border (Fig. 5D). In lateral view In lateral view (Fig. 6A) parameres fl attened; a strongly sinuous apex, never slightly sinuous or truncated, with a deep excavation near the upper angle; rounded upper angle; lower angle much less than 90°. In dorsal view (
HEAD. Green with bright yellow. Dorsal surface with small spots equally spaced. Two clypeal teeth triangular, with rounded apex, separated by a V-shaped emargination, with two dorsal tufts of setae and two ventral tufts. Clypeo-genal suture present (Fig. 5A).
HYPOMERON. Dark blue and black, chagrinated microsculpture; sparse setae present on anterior portion and anterolaterally; strong transverse carina along ⅔ of the whole length; anterior portion little excavated, with prominent teeth anterolaterally (Fig. 5C).
PYGIDIUM. As wide as long; blue with bright green and yellow; basal margin little expanded (Fig. 5D).
PARAMERES. Flattened laterally; on lateral view, apical portion with a long sinuosity; on dorsal view, central membranous portion enlarged in the centre (Fig. 6A-B).
INTERNAL SAC. Fronto-lateral peripheral sclerite (FLP) involving axial sclerite (A), forming a central duct with spiniform apex; subaxial sclerite (SA) absent; medial peripheral sclerite (MP) semicircular, widely emarginated, with the internal margin with a lobe on the extremity (without central tooth); external margin sinuous with a lobe on the extremity, lobes separated by a U-shaped margin; apex of FLP + A involved by MP; superior right peripheral sclerite (SRP) circular with lateral prolongation in the dorsoventral direction (Fig. 6C-D). MORPHOLOGICAL VARIATION. Body length (except the head) ranges from 9.5 mm to 12 mm; pronotum width from 6 to 7.5 mm. Pronotum with bright refl ections, according to the viewing angle, between different intensities of green, red and yellow.

Remarks
For a long time, this species was identifi ed as Canthon auricollis Redtenbacher, 1868, but the examination of the type specimens of both nominal species allowed Vaz-de-Mello & Cupello (2018a) to conclude that, in fact, the latter name refers to a another species belonging to Canthon s. str., closely related to C. lividus Blanchard, 1846. It is an insect that can be considered very rare and can only be collected at altitudes usually over 1000 m. The predominance of pronotal sheen varies from golden yellow to red.

Distribution
High altitude in the Atlantic Forest along the coast of Brazil, in the states of Minas Gerais, Espírito Santo and Rio de Janeiro (Fig. 10).  Diagnosis Canthon terciae sp. nov. can be distinguished by the following combination of characters: elytra and pronotum dorsally red or green reddish (Fig. 7A). Legs with fl at metafemur at the base, with no punctures or groove (Fig. 7B). Hypomeron with thin transverse carina between the anterior and posterior portion, projecting to the median region, never near the lateral margin, anterior region without excavation (Fig. 7C). Propygidium with strong carina near pygidium edge (Fig. 7D). Parameres, in lateral view (Fig. 8A): fl attened; truncated apex, sub-straight, never sinuous; slightly rounded upper angle; lower right angle. In dorsal view (Fig. 8B): membranous portion separating the parameres, wider in the central region and narrower at the base and at the apex. Internal sac (Fig. 8C-D). Peripheral fronto-lateral sclerite (FLP) involving the axial sclerite (A), the two structures form a complex with a central duct, wider at the base, which gradually tapers to the apex, which is much thinner; subaxial sclerite (SA), smaller than in C. staigi, lateral to the FLP + A complex; peripheral medial sclerite (MP), without central dentin at the inner margin, distal to A, lateral in relation to FLP + A tapered region, with the sharper part passing within a semiduct formed by MP; superior right peripheral sclerite (SRP) with lateral angular prolongation.

Etymology
This species is named in honour of Dr Tercia Vargas dos Santos, who developed phylogeographical studies with the subgenus Peltecanthon and reinforced our taxonomic decision.  COLOUR. Dorsally red with bright green. Ventrally green with bright red (Fig. 7A).

Holotype
HEAD. Red with bright green. Dorsal surface with small spots equally spaced. Two clypeal teeth triangular, with rounded apex, separated by a V-shaped emargination, with two tuft of setae dorsally and two tufts ventrally. Clypeo-genal suture present (Fig. 7A).
HYPOMERON. Green, chagrinated microsculpture. Sparse setae present on anterior portion and anterolaterally. With thin transverse carina between the anterior and posterior portion projecting to the median, region anterior not excavated (Fig. 7C). Anterior portion fl at, with a little tooth anterolaterally (Fig. 7C).
PYGIDIUM. As wide as long. Red with bright green. Basal margin expanded, forming a strong carina in V-form between pygidium and propygidium.
PARAMERES. Flattened laterally. On lateral view, apical portion ventrally truncated, dorsally a little curve. In dorsal view, central membranous portion enlarged in the centre (Fig. 8A-B).
MORPHOLOGICAL VARIATION. Body length (except the head) ranges from 8.5 to 11.5 mm; pronotum width from 6 to 7.5 mm. Colour: dorsally green with bright red. Legs: metafemoral ventral surface not completely smooth, with some punctures.

Remarks
This new species is much more similar to C. staigi than to the other two species of Peltecanthon. The differences between them are very subtle, and there are great morphological similarities between them, in the main characters that differentiate the species of this subgenus; the main differences observed are in the sclerites of the internal sac (exactly in MP). In addition to the sclerite, these species (C. staigi and C. terciae sp. nov.) can be differentiated only by the characters of the dorsal colour and base of the metafemur, without any need for dissection.

Geographic distribution
Northern Brazilian Atlantic Forest, in the states of Rio Grande do Norte, Paraíba, Pernambuco and Sergipe (Fig. 10).

Discussion
Phylogenetic relationships between the groups within Canthon are still poorly understood. Despite the fact that Medina et al. (2003) placed Peltecanthon near Goniocanthon, their analysis does not consider molecular data and lacks some important species. However, there is a close external resemblance between the two subgenera (Peltecanthon and Goniocanthon), but we cannot conclude at this point whether this resemblance is due to morphological convergence or common ancestry.
However, despite their colour and dorsal resemblance, one can readily distinguish the two genera by looking at the pygidium (fl at in Peltecanthon, strongly convex in Goniocanthon) and metafemora (claviform in Peltecanthon, regular in Goniocanthon) (Nunes et al. 2018). Both characters are very useful in avoiding misidentifi cation, especially between C. (Peltecanthon) staigi and C. (Goniocanthon) smaragdulus (Fabricius, 1781), both blue-coloured species from the Brazilian Atlantic Forest.
At fi rst glance, Peltecanthon species diversity is related to historically stable areas in the Atlantic Forest, as defi ned by Carnaval & Moritz (2008). Recent published data on Scarabaeinae (genus Dichotomius Hope, 1837) also reveal that the northern part of the Atlantic Forest harbours several endemic species (Valois et al. 2017). Extra attention is needed to remnants of Atlantic forest: fi rst, because of a considerable number of new endemic species awaiting description around Alagoas, Pernambuco and Sergipe forest remnants. Second, these remnants are in great danger, mainly from anthropogenic activities (Zwiener et al. 2017).
Little information is available on the ecology and behaviour of Peltecanthon from labels and from the published literature. In general, all species seem to be attracted to mammalian faeces and carrion. The occurrence of C. staigi does not seem to depend on well-preserved habitats, and it is sometimes the 'last' Scarabaeinae species in heavily disturbed environments (pers. obs. RVN). Of the other species, C. splendidus is the rarest, C. terciae sp. nov. appears to be quite common in parts of the northeast coast and C. haroldi is very abundant in the region of Linhares in Espírito Santo.
Further descriptive taxonomic work on Canthon and other Deltochilini groups is required. It is imperative to develop morphological and molecular phylogenies to provide better classifi cations, and a better understanding of Neotropical Scarabaeinae systematics and evolution. However, alphataxonomy description works are still essential to elucidate, at least, the diversity of the Atlantic Forest Scarabaeinae.