Xuedytes Tian & Huang

Tian, Mingyi, Huang, Sunbin & Wang, Dianmei, 2017, Discovery of a most remarkable cave-specialized trechine beetle from southern China (Coleoptera, Carabidae, Trechinae), ZooKeys 725, pp. 37-47 : 37-39

Xuedytes Tian & Huang gen. n.

Type species.

Xuedytes bellus Tian & Huang, sp. n.

Generic characteristics.

Highly modified aphaenopsian trechines, body shape, in particular prothorax, similar to that in Giraffaphaenops , but elytra generally like in Dongodytes (s. str.) (Fig. 1); large-sized, with body (especially prothorax and elytra) and appendages thin and extremely elongated, eyeless and unpigmented; fore body part (head including mandibles, plus prothorax) much longer than, or as long as (excluding mandibles) elytra, respectively; body smooth; three pairs of frontal setiferous pores present on head; mandibles thin and elongated, feebly curved apically, longer than head width, right mandible edentate; labial suture completely missing; mentum bisetose on either side of tooth at base, base broadly concave; mental tooth simple, short and blunt at tip; submentum 8-setose; ligula bisetose at apex (Fig. 2); antennae very long, antennomeres 10 and 11 extending beyond elytral apices. Prothorax similar to that of Giraffaphaenops , wider than head, very strongly elongated, much longer than head including mandibles, propleura distinctly tumid in basal 1/3, visible from above; pronotum barrel-shaped, thin and distinctly elongated, lateral margins visible throughout from above, slightly narrower than head; hind latero-marginal setae absent, but two long latero-marginal setae plus two or three additional short setae present from middle to front. Elytra similar to those in Dongodytes (s. str.), narrow anteriorly and dilated posteriorly, side margins narrowly bordered throughout, shoulders lacking; striae virtually missing, only weakly traceable; two dorsal and the pre-apical setiferous pores present, each with a very long seta; chaetotaxy similar to that in Dongodytes (s. str.). Protibia smooth, without longitudinal sulcus; protarsomeres not modified in male. Ventrites VII bisetose apically in male, but quadrisetose in female. Male genitalia moderately sclerotized, small, strongly curved ventrally in lateral view, with a quite large and thin sagittal aileron; apical lobe wide and broad in dorsal view; parameres much shorter than median lobe, yet well-developed.

Discussion.

Xuedytes Tian & Huang, gen. n. is undoubtedly the most remarkable cavernicolous trechine genera as regards the extremely elongated prothorax and elytra. It may be considered as a lineage intermediate between Giraffaphaenops and Dongodytes (Fig. 3). Superficially it resembles Giraffaphaenops because of the similarly thin and strongly elongated body, especially the prothorax. Its elytra, however, are quite similar to those of Dongodytes (s. str.). The most striking character states of Xuedytes are as follows: (1) Prothorax much longer than head; (2) Elytra very narrow and strongly elongated; (3) Three pairs of frontal pores present on head; and (4) Right mandibular tooth obsolete.

Although Xuedytes is similar to Giraffaphaenops , there are several important differences: (1) Prothorax and elytra much more strongly elongated in Xuedytes than in Giraffaphaenops ; (2) Head subquadrate, slightly convex laterally, not contracted posteriad in Xuedytes (vs. inversed triangular, with a well-marked neck constriction in Giraffaphaenops ); (3) Entire lateral margins of pronotum visible from above in Xuedytes (vs. invisible from above in front half in Giraffaphaenops ); and (4) Two pairs of latero-marginal setae present behind middle of pronotum in Xuedytes (vs. absent in Giraffaphaenops ) (Fig. 3).

Apart from the differences in prothoracic features, Xuedytes is easily distinguished from Dongodytes (s. str.) by the following characteristics: (1) Head thicker and broader, not narrowed posteriad in Xuedytes (vs. thinner and evidently narrowed posteriad, forming a long and distinct neck constriction in Dongodytes ); (2) Three pairs of frontal pores present in Xuedytes , instead of only one pair in Dongodytes ; (3) Elytral striae completely obliterated in Xuedytes (vs. partially visible in Dongodytes ) (Fig. 3).

Furthermore, differences between the new genus and both Giraffaphaenops and Dongodytes are also evident regarding the structure of the male genitalia (Fig. 4). The median lobe of the aedeagus is shorter in Xuedytes , but thicker, especially so at the base, with a thinner, almost transparent sagittal aileron.

Etymology.

"Xue + dytes". “Xue” in Chinese means “cave”, to indicate that the beetles are cavernicolous. Gender masculine.

Generic range.

China (Guangxi Zhuang Autonomous Region).