Triodontus Westwood, 1845

Frolov, Andrey V., Montreuil, Olivier & Akhmetova, Lilia A., 2016, Review of the Madagascan Orphninae (Coleoptera: Scarabaeidae) with a revision of the genus Triodontus Westwood, Zootaxa 4207 (1), pp. 1-93 : 57-58

Genus Triodontus Westwood, 1845

Triodontus Westwood, 1845: 172 ; Paulian 1977: 1208.

Triodentus (lapsus calami): Paulian 1937: 13.

Orphnidius Benderitter, 1914b: 83 ; objective junior synonym. Type species: Orphnus nitidulus Guérin-Méneville, 1844 , by monotypy.

Diagnosis. Triodontus are small to mid-sized (length 6.5–17.0 mm) beetles, with uniform brown to almost black coloration. Labrum bilobate, slightly sinuate in the middle and relatively feebly protruding past frontoclypeus; length in the middle is 1/6 width (in dorsal view). Mandibles subsymmetrical. Frontoclypeus with rounded anterior margin, with tubercle or horn in males; females have frontoclypeus without tubercle or with minute tubercle. Pronotum of larger males of most species with a bulge medially, large excavations aside the bulge, and with 2 ridge-shaped tubercles laterally of each excavation. Females with convex pronotum without excavations or tubercles. Propleurae smoothly convex, without carinae separating anterolateral areas from basal area. Prosternum with a distinct longitudinal ridge in the middle, slightly tapering caudally. Scutellum rounded apically, about 1/15 length of elytra. Elytra convex, smooth except for base, with marked striae in some species, with feebly marked humeral humps. Wings fully developed. Metepisternon triangular, tapering caudally, with slightly widened anterodorsal angle slightly overlapping epipleuron. Protibiae with 3 outer teeth, not crenulated basad of the teeth. Apices with 3 robust, spur-like setae and a few small setae. Protarsi about 3/4 length of protibiae. Claws 1/3 length of apical tarsomere. Apical protarsomere as long as tarsomeres 3 and 4 combined, as thick as other tarsomeres. Ventral surface of protibiae with a longitudinal keel. Mesothoracic and metathoracic legs similar in shape; metafemora and metatibiae slightly longer than mesothoracic legs. Tibiae somewhat triangular, with 2 apical spurs, with inner margin only slightly concave. Longer tibial spur as long as or slightly longer than 2 basal tarsomeres. Claws about 1/3 length of apical tarsomere. Ventral sides of femora almost impunctate, with sparse, long setae. Phallobase strongly sclerotized dorsally and with a thin membrane ventrally. Parameres relatively short, complex, consisting of outer and inner lobes, without setae. Internal sac of aedeagus with 1 characteristic symmetrical sclerite or a group of fused sclerites.

Diagnostic characters. The most reliable character to differentiate Triodontus species is the shape of the parameres. The shape of the prothoracic armature, especially when fully developed, is specific to species groups.

Species composition, distribution, and habitat. Triodontus is endemic to Madagascar. It is the second most speciose orphnine genus of the island with 15 species. The species are distributed throughout the island but mostly in the eastern and northeastern parts. The majority of the localities agree well with the current distribution of the remnants of indigenous rain forests.