Rhytomus Génier & Saxton, 2025

Génier, François, Gunter, Nicole L. & Saxton, Natalie A., 2025, Rhytomus Génier & Saxton: A new dung beetle genus from New Guinea with five new species and phylogenetic insights (Coleoptera: Scarabaeidae: Scarabaeinae), Zootaxa 5575 (1), pp. 87-110 : 93-95

Rhytomus Génier & Saxton , new genus

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Types species. Tesserodon elongatum van Lansberge, 1885 .

Diagnosis. The presence of a trochanterofemoral pit combined with a pseudepipleuron, the presence of a posterior hypomeral carina and well-defined elytral striae 9 and 10 will separate Rhytomus from all the other genera in New Guinea. Within the Australasian endemic clade, Rhytomus can be distinguished from other genera by those previous characters listed in conjunction with having 9 elytral striae, and wide eyes with an interocular space 3–6 times the eye width.

Description. Body. Total length 3.0– 6.3 mm. Tegument hard, brittle. Color dark reddish brown to black (teneral specimens lighter in color), ventral surface and legs usually lighter in color, lacking metallic sheen. Head. Anterior edge of clypeus with two clypeal teeth, with or without emargination on external side of each tooth. Dorsal part of eyes wide ( Fig. 4A,B ), inner edge straight basally, outer edge arcuate, with at least 12 facets along its widest portion. Ocular canthus incomplete. Occiput of head simply rounded ( Fig. 4C,D ). Antennae nine segmented, with 3-antennomere club, club antennomeres approximately equal width. Antennomeres 7 and 8 lacking median cavity.

Pronotum. Basal edge of pronotum broadly arcuate. Posterior hypomeral carina present, almost as long as half lateral pronotal edge. Anterior edge lacking membranous imbrication, anterior marginal bead very narrow. Elytra. Elytra with 9 striae, 7 on disc and 2 on the pseudepipleuron adjacent to the epipleural edge ( Fig. 4D ). Stria 8 missing. Stria 9 effaced anteriorly, fused or very closely set with tenth stria past basal third to posterior declivity where it is distinct again. With a well-defined pseudepipleural fold from base to apical declivity outside stria 7. Laterobasal elytral pit present or absent ( Fig. 4A ). Hind wings. Present, fully developed. Pygidium. Deeply and narrowly sulcate across the base, sulcus usually wider and deeper laterally ( Fig. 8 ). Pterothoracic ventrite. Mesepimera with coarse semicircular ocellate punctures. Abdominal ventrite. Ventrite 6 approximately as long as 1–5 combined along midline. Legs. Protibiae ( Fig. 4E ) of male abruptly internally expanded apically, distal edge of internal angle with a row of contiguous spiniform setae flanked posteriorly by a row of long squamiform setae, with more or less elongated triangular spur. Protibiae distally straight with 3 teeth on outer edge, each tooth with two groups of setae dorsally. Prothoracic legs with trochanterofemoral anterior pit ( Fig. 4C ), trochanter excavated dorsally for reception of inner apical edge of protibia. Protarsi with 5 tarsomeres, tarsomere 1 and 5 longer. Long, setae on all tarsomeres or tarsomere 1 lacking setae. Male mesotibiae with dense setae on ventral edge. Metatibiae of males with well-developed tooth on inner apical angle. Mesotarsi with 5 tarsomeres, tarsomere 2 about same length as tarsomere 5. Metatarsomere 1 widest, metatarsomere 2 equal to metatarsomere 5 in length, all tarsomeres with long setae ventrally. Claws simple or slightly angulate at base. Metacoxal connecting membrane apodeme present, oval (internal). Genitalia. Aedeagus with parameres asymmetrical, right paramere apically bent downwards and expanded, left paramere more or less bent downward apically or simply rounded ( Figs. 9 , 10 ). Spermatheca Vshaped, with or without apodeme distally and basally.

Etymology. Based on the combination of two Greek words. The feminine noun ῥῠτῐ́ς (rhytís) meaning wrinkle, crease and the masculine noun ὦμος (omos) meaning shoulder, the terminal component transliterated in Latin with the masculine ending -us (ICZN art. 30.1.2). The name refers to the presence of a crease on the humeral surface of the elytron.

Distribution. Papua New Guinea and Indonesia (Seram Island, Waigeo Island and Papua). Specimens collected at elevations from 3 m to 2050 m ( Fig. 5 ).

Remarks. Tesserodon seramicum Krikken & Huijbregts, 2009 (described from Seram Island, Indonesia) and Tesserodon waigeoensis Ochi, Kon & Hartini, 2017 (described from Waigeo Island, West Papua) are from outside the study area. However, examination of the illustrations provided in the original descriptions and images of a specimen (RMNH.INS.1488474) substantiate their transfer to the genus Rhytomus and should be combined as follows: Rhytomus seramicus ( Krikken & Huijbregts, 2009) , new combination and Rhytomus waigeoensis ( Ochi, Kon & Hartini, 2017) , new combination. Spermathecal morphology was studied only for species where enough material was available. Males of R. heurni Paulian, 1937 new combination and R. setulosus ( Balthasar, 1965) new combination are unknown; the online identification key will be updated when additional material becomes available.

Species checklist

Rhytomus elongatus ( van Lansberge, 1885) , new combination (type species) Rhytomus fervidus Saxton & Génier , new species

Rhytomus heurni ( Paulian, 1937) , new combination

Rhytomus howdeni ( Paulian, 1985) , new combination

Rhytomus larseni Saxton & Génier , new species

Rhytomus latidentatus Saxton & Génier , new species

Rhytomus papuanus ( Paulian, 1985) , new combination

Rhytomus seramicus ( Krikken & Huijbregts, 2009) , new combination Rhytomus setulosus ( Balthasar, 1965) , new combination

Rhytomus sodalis Saxton & Génier , new species

Rhytomus vanus Saxton & Génier , new species

Rhytomus waigeoensis ( Ochi, Kon & Hartini, 2017) , new combination

Figures

FIGURE 4. Diagnostic characters of Rhytomus. A, dorsal head showing emargination and interocular space (R. howdeni); B, dorsal head showing lack of emargination and interocular space (R. fervidus) C, ventral view of male foreleg (R. latidentatus); D, lateral view of elytra (R. vanus); E, dorsal view of male protibia (R. latidentatus).

FIGURE 5. Distribution of Rhytomus in mainland New Guinea. Note that some distribution points are extrapolated based on best available data, view treatment of each species for more detail.

FIGURE 8. Pygidium of Rhytomus species. A, male R. fervidus; B. female R. heurni; C, male R. howdeni; D, male R. larseni; E, male R. latidentatus; F, male R. papuanus; G, female R. setulosus; H, male R. sodalis; I, male R. vanus. Scale bar = 0.2 mm.

FIGURE 9. Male aedeagus of Rhytomus species, left lateral, dorsal, right lateral.A, R. elongatus; B, R. fervidus; C, R. howdeni; D, R. larseni. Scale bar = 0.5 mm.

FIGURE 10. Male aedeagus of Rhytomus species, left lateral, dorsal, right lateral. A, R. latidentatus; B, R. papuanus; C, R. sodalis; D, R. vanus. Scale bar = 0.5 mm.