Tetragus Duarte and Grossi, 2022

Costa, Leidiane O., Duarte, Paulo R. M., Iannuzzi, Luciana & Grossi, Paschoal C., 2022, Taxonomic revision and notes on natural history of the enigmatic beetle genus Gibboryctes Endrödi (Coleoptera: Melolonthidae: Dynastinae), Journal of Natural History 56 (1 - 4), pp. 191-225 : 217-218

Tetragus Duarte and Grossi , gen. nov.

( Figures 5 ; 6 (e); 7(e); 8(e); 9(d); 10(g,h); 11(e); 13(d); 14(a))

Type species

Strategus waldenfelsi Endrödi, 1977 , here designated.

Diagnosis

Tetragus gen. nov. is separated from other Neotropical genera of Oryctini by the following combination of characters: males with nearly subrectangular body in lateral view ( Figure 5 (b)); mandibles bidentate, with apical tooth broadly truncated at apex and larger than subapical tooth ( Figure 7 (e)); maxillary galea wider at middle than basis, provided with strong scythe-shaped teeth on inner margin ( Figure 8 (e)); pronotum bearing a deep and wide concavity in both sexes ( Figures 9 (d) and Figures 11 (e)); elytral surface with deep and ocellate punctures; protibiae with 4 short teeth on outer margin ( Figure 9 (d)); ventrite V about 1.5 times longer than ventrite VI in female ( Figure 13 (d)).

Generic description

Length: 22.6–32.3 mm. Width: 10.8–14.1 mm. Strong sexual dimorphism; body elongate, oval in dorsal view, subrectangular in lateral view; dorsal surface glabrous; ventral surface densely covered with yellow setae. Colour: Nearly completely black; protibiae sometimes dark reddish. Head: Slightly transverse (1.1 times wider than long). Clypeus triangular, acuminate and slightly reflexed anteriorly, surface finely punctate, glabrous. Frontoclypeal suture with a conical, short tubercle at middle. Frons glabrous, finely punctate at disc, smooth on a transverse area posteriorly; sides with large, deep, C-shaped, coalescent punctures. Ocular canthus transverse, subrectangular, rugopunctate. Mouthparts: Labrum transverse (3 times wider than long), parabola-shaped, transversely covered with a fringe of bristles posteriorly ( Figure 6 (e)). Mandibles with 2 teeth on outer margin (1 apical, 1 subapical) separated by a narrow notch; teeth slightly raised above clypeus laterally; apical tooth broadly truncated; subapical tooth rounded, clearly smaller compared to apical tooth ( Figure 7 (e)). Maxillary galea transversely wider at middle than basis; outer margin rounded; inner margin with 6 teeth (3 apical, 2 medial, 1 basal); apical and medial teeth larger, scythe-shaped; basal tooth triangular, smaller than previous ones ( Figure 8 (e)). Maxillary palpomere II subequal in length to palpomere IV. Labium rounded laterally at basal half; apical half convergent towards a wide, truncated apex; surface densely surrounded with large, deep, bristled punctures; disc with scarce bristles. Antennae: 10- segmented; club oval, subequal in length to antenomeres II–VII combined; scape clavate, densely setose. Thorax: Pronotum, in dorsal view, with complete border, anteriorly with a forward produced horn at middle of anterior margin, posteriorly followed by a broad, deep, U-shaped concavity, reaching nearly to posterior margin ( Figure 9 (d)); in lateral view, pronotum strongly convex dorsally, with sinuous lateral margin, horn obliquely produced regarding antero-posterior body axis; discal surface of concavity covered with large, ocellate, irregularly scattered punctures; sides smooth, posterior area finely punctate. Scutellar plate subtriangular, irregularly punctate on anterior area, smooth posteriorly. Elytra with 10 well-marked longitudinal striae (1 sutural, 5 discal, 4 lateral); striae anteriorly covered with large, deep, oval punctures, becoming shallow towards posterior area; first interstria covered with large, ocellate, oval punctures; other interstriae finely punctate. Legs: Protarsi with sickle-shaped claws; protarsomere V subequal in length to tarsomeres II–IV combined; tarsomeres I–IV subequal in length. Protibiae with 4 short, triangular, as wide as long teeth on outer margins ( Figure 9 (d)); teeth decreasing in size from basal to apical; dorsal surface with a longitudinal double row of bristled carinae. Mesofemora transverse, oval, densely setose. Mesotibiae with 2 carinae on outer surface (1 basal, 1 medial); apex truncated; medial carina and apex covered with stout, triangular spinules like setae. Metafemora wide compared to mesofemora; discal area glabrous, from smooth to finely punctate. Metatibiae similar to mesotibiae. Meso- and metatarsi similar in shape; tarsomeres I–IV decreasing in size; tarsomere V subequal in length to tarsomeres II–IV combined. Abdomen: Tergite VII coarsely rugopunctate, with no stridulatory apparatus. Tergite VIII strongly convex, completely, densely setose; sides rugose, disc finely punctate. Ventrites II–V subequal in length, rugopunctate, setose on sides; discal area glabrous, finely punctate; ventrite VI shorter compared to ventrite V, surface finely punctate, broadly emarginate posteriorly, covered with setae on posterior margin. Venter: Prosternal process triangular, densely punctate, setose. Aedeagus: Parameres, in dorsal view, symmetrical, finely punctate, subparallel, wide at basal half, narrow at middle, becoming wide at apical half, with scarce bristles scattered on inner margins ( Figure 10 (g)). Parameres, in lateral view, subequal in length to phallobasis, wide dorsoventrally at basal half, narrow dorsoventrally at apical half, slightly deflexed apically; ventral surface with a basal carina strongly produced downward ( Figure 10 (h)).

Sexual dimorphism

The female can be distinguished from the male in the following aspects: Head: Surface coarsely rugopunctate ( Figure 11 (e)); clypeus subtrapezoidal or subtriangular ( Figure 11 (e)). Thorax: Pronotum with no horn, only with 2 transverse, flattened tubercles adjacent to middle of anterior margin; anterior and concavity surfaces densely rugopunctate ( Figure 11 (e)). Legs: Metafemora covered with well-marked, oval punctures. Abdomen: Tergite VIII from flattened to slightly convex in lateral view. Ventrite V about 1.5 times longer than ventrite VI ( Figure 11 (d)); ventrite VI with arched posterior margin.

Specific composition

Tetragus waldenfelsi ( Endrödi, 1977) and Tetragus impunctatus ( Dupuis, 2019) .

Etymology

Tetragus is an anagram originating from the word ‘Strategus’, formed by the exclusion of the first ‘s’ plus an exchange of position between the syllable ‘ra’ and the vowel ‘e’. The name is masculine in gender.

Remarks

Tetragus gen. nov. resembles Strategus in the tuberculate head and pronotum with an anterior horn but is separated by the bidentate mandibles; metatibia truncated at apex; tergite VII without stridulatory apparatus; female pronotum bearing a strong and transverse anterior tubercle, combined with a deep concavity.

Figures

Figure 5. Tetragus waldenfelsi (Endrödi, 1977). (a,b) Male habitus in dorsal and lateral views, respectively; (c,d) female habitus in dorsal and lateral views, respectively.

Figure 6. Labrum in dorsal view. (a) Gibboryctes szelenyii Endrödi; (b) Gibboryctes ebeninus sp. nov.; (c) Gibboryctes endroedii sp. nov.; (d) Heterogomphus gracilicornis Prell; (e) Tetragus waldenfelsi (Endrödi).

Figure 7. Right mandible in dorsal view. (a) Gibboryctes szelenyii Endrödi; (b) Gibboryctes ebeninus sp. nov.; (c) Gibboryctes endroedii sp. nov.; (d) Heterogomphus gracilicornis Prell; (e) Tetragus waldenfelsi (Endrödi). Red arrows indicate the apical tooth in (a–e), striate molar in (d).

Figure 8. Right maxilla in ventral view. (a) Gibboryctes szelenyii Endrödi; (b) Gibboryctes ebeninus sp. nov.; (c) Gibboryctes endroedii sp. nov.; (d) Heterogomphus gracilicornis Prell; (e) Tetragus waldenfelsi (Endrödi). Red arrows indicating triangular galea in (a), elongate maxillary palpomere II in (b), lobed inner margin of galea and stipe with triangular lobe in (c), pointed and triangular teeth on galea in (d), scythe-shape d teeth and rounded inner margin of galea in (e).

Figure 9. Detail of head, pronotum and prothoracic legs of males in dorsal view: (a) Gibboryctes szelenyii (Endrödi); (b) Gibboryctes endroedii sp. nov.; (c) Heterogomphus gracilicornis Prell; (d) Tetragus waldenfelsi (Endrödi).

Figure 10. Aedeagus with parameres in dorsal and lateral views, respectively. (a,b) Gibboryctes szelenyii Endrödi; (c,d) Gibboryctes endroedii sp. nov.; (e,f) Heterogomphus gracilicornis Prell; (g,h) Tetragus waldenfelsi (Endrödi).

Figure 11. Detail of head, pronotum and prothoracic legs of females in dorsal view: (a) Gibboryctes szelenyii Endrödi;(b) Gibboryctes ebeninus sp. nov.; (c) Gibboryctes endroedi sp.nov.; (d) Heterogomphus gracilicornis Prell; (e) Tetragus waldenfelsi (Endrödi). Arrow indicates punctate frons in (b).

Figure 13. Detail of ventrites I–VI of females. (a) Gibboryctes szelenyii Endrödi; (b) Gibboryctes ebeninus sp. nov; (c) Gibboryctes endroedii sp. nov.; (d) Tetragus waldenfelsi (Endrödi). Red arrows indicate the proportions of ventrites V and VI.