Rovnoscydmus Jałoszyński & Perkovsky, 2016, gen. n.
Creators: name: Jałoszyński, Paweł
name: Perkovsky, Evgeny
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Rovnoscydmus

description: † Rovnoscydmus gen. n.
Type species: Rovnoscydmus frontalis (here designated).
Diagnosis. A genus of Glandulariini with loosely assembled antennae gradually thickening distally or with very indistinctly demarcated club composed of antennomeres IX–XI; basisternal part of prosternum about as long as coxal part and not demarcated posteriorly by carina; notosternal sutures complete; hypomeral ridges present; prosternal intercoxal region lacking process or carina; mesoventrite lacking median carina between mesocoxae but indistinctly carinate in front of mesocoxae; metaventral intercoxal process narrow and notched at middle; lateral margins of metacoxae distant from lateral margins of metaventrite; pronotum lacking lateral edges or carinae, with short median transverse antebasal groove, lacking pits; each elytron with one small and asetose basal fovea; prothorax and possibly also tempora with thick bristles (not visible in some specimens).
Description. Body (108–164) elongate, relatively slender and strongly convex, with distinctly marked constriction between head and pronotum and between pronotum and elytra, BL 0.64–1.10 mm.
Head capsule (Figs 112–114, 118–119, 123–124, 129, 134, 137–138, 142–144, 148–150, 153–154, 159, 163– 164) with anterior part (in front of occipital constriction) subtrapezoidal and short, eyes located anteriorly, large, strongly convex and coarsely faceted; tempora (Figs 112, 124, 138, 149; tm) about as long as eyes or slightly longer or shorter; occipital constriction (Figs 112, 159; occ) about as broad as frons between eyes or slightly narrower; frons (Figs 112, 118, 123, 149, 159; fr) subtrapezoidal, posteriorly confluent with strongly transverse vertex (Figs 112, 118, 123, 149, 159; vt); clypeus (Fig. 113) not demarcated from frons by groove. Tempora in most specimens lack thick bristles, but in K-7350 (Fig. 149) several short bristles can be seen.
Antennae (Figs 112–114, 118–119, 123–124, 133–134, 137–138, 142–143, 148–150, 153–154, 159, 163–164) relatively long, loosely assembled, gradually thickened distally or with very indistinctly demarcated club composed of antennomeres IX–XI.
Pronotum (Figs 112, 118, 123, 128, 133, 138, 142, 148–150, 153, 163–164) in dorsal view oval with weakly arcuate or nearly straight anterior and posterior margins, sides strongly rounded, anterior and posterior pronotal corners weakly marked, obtuse-angled and blunt; pronotum broadest in anterior half or near middle; pronotal base with short transverse antebasal groove (Fig. 112; abp) slightly deepened at each end. Sides of pronotum lacking edges or carinae; in some specimens (Figs 123, 128–129, 143, 148, 153) variously developed thick bristles can be seen on lateral pronotal margins and/or prothoracic hypomera.
Prosternum with basisternal part (Figs 114, 119, 124–125, 129, 134, 143, 154; bst) long, as long or nearly as long as coxal part, notosternal sutures (Figs 114, 119, 129, 143; nss) complete; interprocoxal region lacking carina or process; prothoracic hypomera (Figs 114, 119, 124, 129; hy) with hypomeral ridges (Figs 114, 129, 138, 143; hyr; but visible only in some specimens, probably because of very small size and a film of air coating the prothorax). It is unknown whether the procoxal sockets are closed or open.
Mesoscutellum (Figs 112, 118, 123, 128, 133, 138, 142, 149, 153) well-visible between elytral bases, small, subtriangular.
Mesoventrite (Figs 114, 119; v2; 125, 160) best exposed in specimens K-347 (Fig. 119), K-25702 (Fig. 125) and K-8972 (Fig. 160), lacking mesoventral intercoxal process between mesocoxae, in front of mesocoxal cavities with pair of impressions functioning as procoxal rests (Figs 119, 125, 160; pcr) separated at middle by carinate but weakly elevated projection of anterior ridge, in specimens K-25702 (Fig. 125) and K-8972 (Fig. 160) setae surrounding each lateral impression are well visible.
Metaventrite (Figs 114, 119, 125, 129, 134, 137, 143, 160; v3) subquadrate or subrectangular and slightly shorter than broad, with slightly rounded sides, posterior margin deeply bisinuate in front of metacoxae but weakly convex laterally, each metacoxa separated from lateral margin of metaventrite by 1/4–1/5 width of ventrite; metaventral intercoxal process (Figs 114, 119, 125, 129, 137, 143, 160; mtvp) narrowly but distinctly separating metacoxae, with distinct median notch. Anterior margin of metaventrite with dense 'wooly' setae forming bisinuate fringe behind posterior margins of mesocoxal cavities (well-visible only in specimens K-25702 (Fig. 125) and K- 8972 (Fig. 160)).
Elytra (Figs 112, 118, 123, 128, 133, 138, 142, 148–149, 153, 158, 163–164) elongate and oval, each with one small but distinct and asetose basal elytral fovea (Figs 112, 118, 123, 128, 133, 138, 142, 149; bef), humeral calli well-marked.
Hind wings in some specimens (e.g., Figs 115, 118) protruding from under elytra, long.
Legs (Figs 112, 114, 118–119, 123–125, 128–129, 133–134, 137–138, 142–144, 148–149, 153–154, 160, 163– 164) moderately long, slender; pro- and mesocoxae suboval, metacoxae strongly transverse; all trochanters small and subtriangular; femora moderately and gradually clavate; tibiae slender, straight or nearly straight; tarsi moderately long and slender, tarsomeres slightly flattened.
Abdomen with six visible sternites (Figs 114, 119, 125, 137, 143, 160; st3–8) subequal in length or with sternite III longer than IV and sternite VIII longest (depends on the position of abdomen and post mortem shrinkage of abdominal segments). Tip of pygidium exposed in some specimens (e.g., Fig. 118; pg).
Distribution and composition. Rovnoscydmus includes two nominal species and nine specimens representing an unspecified number of undescribed species from the Eocene of Europe (Fig. 38), area currently within northwestern Ukraine.
Etymology. The name Rovnoscydmus is derived from the locality name Rovno and the stem - scydmus commonly used in generic names of Scydmaeninae. Gender masculine.
Remarks. This is another genus of Glandulariini with the metacoxae broadly separated from the lateral metaventral margins, similarly as in Glaesoconnus, Amimoscydmus Leptocharis, Parapseudoconnus (Neuraphomimus), some species of Sciacharis and Scydmaenozila. Rovnoscydmus differs from all the extant genera with similar metacoxae in the same way as Glaesoconnus, i.e., in having the mesocoxae contiguous, not separated by carinate and elevated mesoventral intercoxal process. Differences between Rovnoscydmus and Glaesoconnus are numerous and include: the antennae slender and loosely assembled in Rovnoscydmus (short and compact in Glaesoconnus); the prothoracic hypomera with hypomeral ridges in Rovnoscydmus (because of very small body this structure is visible only in some studied specimens; Glaesoconnus lacks hypomeral ridges); the pronotal base bearing short median transverse groove in Rovnoscydmus (four pits in Glaesoconnus); and each elytron with one basal fovea in Rovnoscydmus (two distinct foveae in Glaesoconnus).
Rovnoscydmus resembles Stenichnus to a lesser extent than Glaesoconnus; it is rather more similar, at least in its general body form, to Microscydmus Saulcy & Croissandeau, 1893. Morphological structures of the latter genus were illustrated in detail in Jałoszyński (2014d). Rovnoscydmus and Microscydmus share similarly slender and very small body (BL about 1 mm and less) and several morphological details, but clearly differ in the elytral bases (in Microscydmus with a large and deep basal impression, missing in Rovnoscydmus), the length of the basisternal part of prosternum (much shorter than coxal part in Microscydmus vs. about as long as coxal part in Rovnoscydmus), the intermesocoxal region (bearing carinate mesoventral process in Microscydmus vs. lacking process in Rovnoscydmus), the metacoxae (laterally adjacent to metanepisternum and lateral metaventral margin in Microscydmus vs. distant from sides of metaventrite in Rovnoscydmus), and in the pronotal base (with two pairs of antebasal foveae, of which the inner pair is usually connected by groove in Microscydmus vs. transverse groove or impression with slightly deepened ends in Rovnoscydmus).
There are also several other extant genera of Glandulariini superficially similar to Rovnoscydmus in the general body form and small size, as the Neotropical Heteroscydmus Franz, 1980 and Amimoscydmus, or Afrotropical Oreoeudesis Franz, 1985. These genera were revised and their morphological structures illustrated in Jałoszyński (2013a, 2015g). All of them have a robust, carinate and elevated mesoventral intercoxal process, a structure missing in Rovnoscydmus.
Among specimens identified as belonging in Rovnoscydmus, some characters are not present, or rather not visible, in all inclusions. The hypomeral ridges can be seen (at least as faint lines) in specimens K-9579, K-26348, K-8970 and K-8968, but not in K-347, K-25702, UA-1556, K-7350, K-3037, K-8972 and K-3322; the lateral pronotal bristles are discernible in specimens K-25702, K-26348, K-8968, K-7350, K-3037 and K-8972 but not in K-9579, K347, UA-1556, K-8970 and K-3322. It seems, however, that the very small and slender body makes these structures difficult to observe, and the silver film of air covering the prothorax obscures some details. All these specimens are interpreted as congeneric, but only two of them can be identified as two distinctly different species, on the basis of a unique modification of the frons (K-9579.) and exceptionally small body, much smaller than all remaining specimens (K-347). It is unclear whether some of the remaining specimens, similar in size to K- 9579, are conspecific with the latter specimen or not, or how many species they represent. For this reason, they are treated below not as sp. 1, sp. 2 and so on, but rather as specimen 1, specimen 2 and so on. Their morphological structures were compiled in the generic diagnosis, so it is important to describe them in as much detail as possible. Further study (based on additional specimens or using high-resolution imaging methods, e.g., the synchrotron tomography) is necessary to verify the hypothesis that these specimens all belong in one genus. Characters seen under light microscopes, although leading to such preliminary conclusions as presented here, do not provide a deciding answer. It is noteworthy that specimens K-8968, K-8970, K-8971 and K-8972 (described below as specimen 4, 5, 8 and? Rovnoscydmus specimen 9) were found in one piece of amber. This suggests that they all not only belong to the same genus, but also may be conspecific. However, it was not possible to find convincing morphological evidence to support or reject such a hypothesis.
description: Published as part of Jałoszyński, Paweł & Perkovsky, Evgeny, 2016, Diversity of Scydmaeninae (Coleoptera: Staphylinidae) in Upper Eocene Rovno amber, pp. 1-85 in Zootaxa 4157 (1) on pages 36-38, DOI: 10.11646/zootaxa.4157.1.1, http://zenodo.org/record/262413