Caucanthobium, Assing, 2018

Assing, Volker, 2018, An enigmatic new genus and species of Anthophagini from Georgia (Coleoptera: Staphylinidae: Omaliinae), Linzer biologische Beiträge 50 (2), pp. 969-976 : 970-974

Caucanthobium nov.gen. ( Figs 1-11 )

T y p e s p e c i e s: Caucanthobium mirandum nov.sp.; present designation.

E t y m o l o g y: The name (gender: neuter) is composed of Cauc (from Caucasus) and the generic name Anthobium. It alludes to the external resemblance to Anthobium and the distribution, which is currently confined to the southwestern Caucasus region.

D e s c r i p t i o n: Body depressed ( Fig. 1 ). Head ( Figs 4-6 ) distinctly transverse, broadest across eyes; dorsally with a pronounced impression near dorsal margin of eye on either side; median dorsal portion distinctly elevated; antocular indentation indistinct; postocular ridge reduced, not visible from above; ocelli pronounced, situated at posterior constriction, separated from each other by a distance slightly greater than the distance between ocellus and posterior margin of eye. Mentum and praementum densely punctate; gular sutures contiguous posteriorly; posterior constriction ventrally with distinct microsculpture and with some coarse granules in the middle. Eyes of moderate size and distinctly convex. Antenna ( Fig. 2 ) elongate and slender; antennomeres IV-IX distinctly oblong, X weakly oblong. Maxillary palpus ( Fig. 6 ) slender; maxillary palpomere IV approximately five times as long as broad and slightly more than twice as long as maxillary palpomere III.

Pronotum ( Fig. 4 ) weakly convex in cross-section, moderately transverse (approximately 1.4 times as broad as long), broadest in anterior half; posterior angles marked; lateral margins broadly explanate, weakly (but distinctly) serrulate, weakly sinuate in posterior half in dorsal view; surface of disc uneven, with pronounced impressions and elevations.

Posterior process of prosternum very long and acute ( Fig. 7 ). Elytra ( Fig. 1 ) weakly convex in cross-section; lateral margins broadly explanate and finely serrulate; punctation seriate laterally and posteriorly. Mesoventrite ( Fig. 7 ) with sharp median carina; posterior process very long and acute, reaching half-way between mesocoxae. Legs long; all tibiae thin and straight, without evident modifications. Protarsus with pronounced sexual dimorphism.

Abdomen ( Fig. 8 ) with rather dense and distinct punctation.

♂: protarsomeres I-IV ( Fig. 3 ) strongly dilated; aedeagus ( Figs 9-10 ) highly derived, small in relation to body size, weakly sclerotized, with laterally (not dorso-ventrally) compressed median lobe, with conspicuous long sclerotized internal structure, and with strongly asymmetric parameres of derived shapes.

♀: gonocoxites short and very broad, basally not completely fused ( Fig. 11 ); styli short and with very long terminal seta.

C o m p a r a t i v e n o t e s: Based on the presence of at least a rudimentary postocular ridge, the structure of the mouthparts, and the shapes and punctation of the pronotum and elytra, Caucanthobium is placed in the Anthobium group of genera within the Anthophagini (see SHAVRIN & SMETANA 2016, 2017). In external characters, the genus most resembles Anthobium, to some extent also Deinopteroloma. It is distinguished from both genera by a highly derived morphology of the aedeagus (weakly sclerotized, strongly asymmetric, median lobe laterally compressed; internal sac with sclerotized internal structure), a strongly reduced postocular ridge, and strongly dilated male protarsi. In addition, it is separated from them as follows:

from Anthobium by the presence of pronounced impressions and elevations on the pronotal disc, a mesoventrite with a pronounced median carina, and by the structure of the female genital segment with short and very broad gonocoxites and short styli;

from Deinopteroloma by much flatter elytra, the absence of a distinct antocular indentation (see SMETANA 1985: figure 47), the shape of the pronotum (Deinopteroloma: pronotum broadest approximately in the middle, lateral margins regularly convex, not sinuate, and usually strongly serrulate), thin and straight tibiae (stout and usually more or less distinctly sinuate in Deinopteroloma), the shape of the head (Deinopteroloma: head usually with a more or less pronounced transverse sulcus anterior to ocelli), and a female genital segment with basally not fully fused gonocoxites.

D i s t r i b u t i o n: The monotypical genus is currently known only from Southwest Georgia, Lesser Caucasus.

Figures

Figs 1-3: Caucanthobium mirandum nov.sp.: (1) habitus; (2) antenna; (3) male protarsus. Scale bars: 1-2: 1.0 mm; 3: 0.2 mm.

Figs 4-8: Caucanthobium mirandum nov.sp.: (4) head and pronotum; (5) head in dorso-lateral view; (6) head in ventral view; (7) thorax in ventral view; (8) apical portion of abdomen. Scale bars: 7: 1.0 mm; 4-6, 8: 0.5 mm.

Figs 9-11: Caucanthobium mirandum nov.sp.: (9-10) aedeagus in lateral and in ventral view; (11) female genital segment. Scale bars: 0.2 mm.