Xestotrogus Reitter 1902
Creators: name: Uliana, Marco
name: Khudhur, Farhad A.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Xestotrogus

description: Genus Xestotrogus Reitter, 1902 status revised
Type species: Rhizotrogus validus Kraatz, 1884, by monotypy
= Cyprotrogus Nikolajev, 2004 new synonym
Diagnosis. Based on characters of males (females are unknown). Integument non-pruinose. Dorsal side subglabrous, with conspicuous setation only on vertex and scutellum. Frons not crested, moderately swollen in the medial area. Clypeus broadly rounded. Labrum transverse, bilobed, densely setose on its whole surface. Dorsal side of pronotum with few minute setae near the anterior angles, some more developed setae may be sparsely present along the anterior margin. Dorsal side of maxillary palps with a flattened area. 10 antennomeres (individual cases of incomplete disjunction observed). Claws toothed at base. Metatibial spurs not significantly dilated, setation of metatarsi not hyper-developed. Phallobase longer than paramera, curved, with a dorsal hump at about mid length and a broad parabolic membranous area anterior to it, connected to paramera. Basal region of paramera fused both dorsally and ventrally. Dorsal portion of paramera short, bearing two well-developed digitiform medial processes, smooth, parted by a deep and narrow cleft. Ventral portion of paramera much longer than dorsal, produced in two long laminar processes parted by a broad gap; such processes laminar, not carinated, sinuous in lateral view. Paramera glabrous on the whole surface.
History and current status. Xestotrogus Reitter, 1902 was introduced as a monotypic subgenus of Rhizotrogus Latreille, 1825, then raised to genus rank by Baraud (1987) and as such accepted by Keith (2002), who added as a second species the Cypriot endemic Ancylonycha nitens Baudi, 1870. The latter had been assigned to the genus Madotrogus since Reitter (1902).
Shortly afterwards, Nikolajev (2004a) downgraded Xestotrogus to subgenus of Xanthotrogus, based on the similarity of paramera, whose peculiar dorsal processes however granted it the preservation of a distinct, subgeneric status. At the same time, he removed A. nitens from it, announcing that it would require a different generic assignment due to the lack of hair on the lower side of paramera, a condition which he considered a diagnostic trait of Xanthotrogus (Nikolajev 2004a, 2004b, 2007) in accordance with the opinion of Medvedev (1966). Thus, to accommodate this species, Nikolajev (2004b) subsequently introduced the monospecific subgenus Cyprotrogus, within the subgenus Dasytrogus (under the name Madotrogus Reitter, 1902, which was in use for the same concept until Branco (2010) evidenced that the nomenclatural rules enforced by ICZN (1999) require the use of its subjective synonym Dasytrogus Reitter, 1902).
In this framework, the placement of Ancylonycha nitens inside Dasytrogus was justified by the absence of setation on the lower side of paramera, while its distinction in a separate subgenus was justified, again, by their peculiar structure. Paramera, exactly as in Xestotrogus, are indeed equipped with two long dorsal processes, a similarity that was interpreted as convergent evolution by Nikolajev (2004b). Such processes are absent in the other species of Dasytrogus, as well as in those of Xanthotrogus, where the corresponding area bears at most two small denticles.
Nikolajev also pursued some preliminary exploration of the endophallic structure of the discussed taxa. His picture was however largely incomplete, also due to the referred difficulty to inflate dry material (Nikolajev 2004b, 2007). He did not publish any information on the species discussed here, although he speculated over the traits expected for Ancylonycha nitens.
New observations and discussion. After direct examination of the taxa involved, it is evident that Nikolajev worked under the wrong assumption that paramera of R. validus (type species of Xestotrogus) are hairy on their lower side, while they are actually glabrous (as are those of A. nitens).
This brings two consequences: first, Xestotrogus fails to fit the current definition of the genus Xanthotrogus, of which it is treated as a subgenus. Second, the only character supporting the placement of R. validus and A. nitens in two distinct genera falls. Pending a sound phylogenetic evaluation, the strong resemblance of their paramera and their evident difference from those of most similar taxa (i.e.: species assigned to Dasytrogus and Xanthotrogus) seem enough to justify a generic treatment on their own for these two species, as proposed by Keith (2002).
The study of their endophalli, formerly unexplored, reveals a common ground plan similar to that observed in some species of Dasytrogus (including the type species D. transcaspicus (Brenske, 1886), see Nikolajev 2004b), and clearly more distinct from the structure observed in Xanthotrogus (see Nikolajev 2007, and M.U., unpublished observations). The endophallites, however, exhibit a remarkable variability in the presence or absence of the same element across the different species (Figs. 31–39). Notably, Nikolajev (2007: 54) even observed an intrapopulational variability in the presence or absence of the same large endophallite, suggesting caution on the taxonomic interpretation of this trait and the need of a better comprehension of its variability at a low taxonomic level.
Concluding, in accordance with the results above, Xestotrogus Reitter, 1902 status revised is removed from subgeneric status under Xanthotrogus Reitter, 1902 and treated as a valid genus, and Cyprotrogus Nikolajev, 2004 is introduced as its new synonym. The genus Xestotrogus contains now three species: X. nitens (habitus in Fig. 1), X. validus (habitus in Fig. 2), and X. sagrmaticus, new species.
description: Published as part of Uliana, Marco & Khudhur, Farhad A., 2025, A revision of the taxonomic status of Xestotrogus Reitter, 1902 and related taxa, with the description of a new species from Iraqi Kurdistan (Coleoptera: Scarabaeidae: Melolonthinae), pp. 477-490 in Zootaxa 5575 (3) on pages 478-480, DOI: 10.11646/zootaxa.5575.3.8, http://zenodo.org/record/14747276