Stenichnus proavus, Jałoszyński, Paweł & Perkovsky, Evgeny, 2016

Jałoszyński, Paweł & Perkovsky, Evgeny, 2016, Diversity of Scydmaeninae (Coleoptera: Staphylinidae) in Upper Eocene Rovno amber, Zootaxa 4157 (1), pp. 1-85 : 63-66

† Stenichnus (s. str.) proavus sp. n.

( Figs 28 , 193–198 )

Type material. Holotype: Late Eocene of Europe , Rovno amber: sex unknown; inclusion in elongate, subtriangular piece of amber 9 mm long with truncated corners ( Fig. 28 ), collection number K-24302 ( SIZK).

Diagnosis. Stenichnus s. str. with pronotal base bearing indistinct median transverse groove or impression flanked at each side by three or four small pits; BL about 1.45 mm; EI 1.48..

Description. Body ( Figs 193–198 ) elongate, relatively stout and strongly convex, nearly black; BL about 1.45 mm.

Head ( Figs 193–198 ) broadest at eyes, HL about 0.25 mm, HW about 0.25 mm; vertex and frons confluent but poorly visible; compound eyes large, strongly convex, oval; tempora seem very short. Punctures and setae on frons and vertex poorly visible. Antennae ( Figs 193–198 ) nearly as short as 1/3 BL, gradually thickened distally, AnL about 0.56 mm, five proximal antennomeres elongate, distal flagellomeres poorly visible, but most likely not elongate, antennomere XI about as long as IX–X together or slightly shorter, about twice as long as broad, with rounded apex.

Pronotum ( Figs 193–194 , 197 ) broadest in anterior half; PL 0.35 mm, PW 0.38 mm; anterior and posterior margins arcuate, lateral margins sinuate, anterior and posterior pronotal corners blunt; base with shallow and diffused transverse antebasal groove ( Fig. 197 ; abg) and lateral groups of 3–4 small and shallow antebasal pits ( Fig. 197 ; abp). Punctures on pronotal disc small but distinct ( Fig. 197 ), separated by spaces 2–3 × as wide as diameters of punctures; setae ( Fig. 197 ) short, sparse, suberect.

Elytra ( Figs 193–194 , 197 ) elongate oval, strongly convex, broadest most likely in front of middle, EL 0.85 mm, EW 0.58 mm, EI 1.48; punctures ( Fig. 197 ) slightly larger but otherwise similar to those on pronotum; setae ( Fig. 197 ) similar to those on pronotum. Scutellum large, subtriangular and well visible between elytral bases.

Legs ( Figs 193–198 ) moderately long, slender, unmodified.

Etymology. The name proavus (a noun in apposition) means "great grandfather, forefather, ancestor" in Latin.

Remarks. Placement of this species in the extant genus Stenichnus is not strongly supported, as some morphological characters in the studied specimen are obscured by turbid amber or hidden under declined head. However, the general body form, the shape and antebasal structures of the pronotum, absent lateral pronotal carinae and sublateral pronotal carinae, the gradually thickened antennae, the 'wooly' setae forming a fringe along posterior margins of the mesocoxal cavities and the large scutellum exposed between elytral bases in combination with the metacoxae touching the lateral margins of metaventrite and the narrow metaventral intercoxal process indicate that this is either a Stenichnus or a genus very close to Stenichnus . The arrangement of the antebasal groove and pits make this species easily identifiable, and its generic placement will be possible to verify if new specimens become available in future. If the placement in Stenichnus is accepted, then the presence of one well-visible and large basal elytral fovea adjacent to the scutellum indicates that this is the nominotypical subgenus; Stenichnus ( Scydmaenichnus Reitter, 1905 ) has two rudimentary foveae ( Jałoszyński 2013b).

Most extant species of Stenichnus have the pronotal base with a transverse row of four or six pits, also a row of large, numerous and irregularly distributed punctures (larger than those on disc) can be found in some representatives of this genus. A transverse impression in addition to pits is unique for St. proavus . However, recently a species with the pronotal base with one lateral pair of shallow pits and a pair of short longitudinal grooves near middle composed of diffused and connected punctures was redescribed ( Jałoszyński 2015i). This demonstrated that the spectrum of antebasal structures in Stenichnus is greater than previously thought, and St. proavus is not as unusual with its antebasal groove as it may seem.

Figures

FIGURES 21 – 34. Specimens of Rovno amber with inclusions of Scydmaeninae. K- 8972, Rovnoscydmus sp. specimen 8 (21); K- 3322, Rovnoscydmus sp. specimen 9 (22); K- 15548,? Rovnoscydmus sp. specimen 10 (23); K- 8971,? Rovnoscydmus sp. specimen 11 (24); K- 6045, Euconnus palaeogenus sp. n. (25); K- 9126, Euconnus sp. 1 (26); K- 24859,? Euconnus sp. 2 (27); K- 24302, Stenichnus proavus sp. n. (28); UA- 2216, Microscydmus sp. 1 (29); K- 6943,? Microscydmus sp. 2 (30); K- 3657 a,? Microscydmus sp. 3 (31); K- 6764,? Scydmoraphes sp. 1 (32); K- 6274, Glandulariini gen. & sp. indet. 1 (33); K- 7089, Glandulariini gen. & sp. indet. 2 (34).

FIGURES 193 – 196. Holotype of Stenichnus proavus sp. n. (K- 24302). Dorsolateral (193), right lateral (194), left lateroventral (195) and nearly anterior (196) views.

FIGURES 197 – 198. Holotype of Stenichnus proavus sp. n. (K- 24302). Dorsolateral (197) and ventrolateral (198) views. Abbreviations: abg, antebasal groove; abp, antebasal pit; bef, basal elytral fovea; lbr, labrum; mtvp, metaventral intercoxal process; mxp 2 – 4, maxillary palpomere II – IV; pg, pygidium; v 3, metaventrite.