Orussus juttagroehnae Vilhelmsen and Perrichot, Vilhelmsen and Perrichot, 2024

† Orussus juttagroehnae Vilhelmsen and Perrichot , sp. nov.

( Figs 6–9 View Figure 6 View Figure 7 View Figure 8 View Figure 9 )

ZooBank registration: urn:lsid:zoobank.org:act: 2195267A- 2F76-4A67-A2BD-893D44C90CD2.

Material examined: Holotype GPIH 5081 View Materials (CCGG no. 1288), a complete female preserved in a piece of Baltic amber dated as Late Eocene ( Priabonian ).

Diagnosis: Ventral coronal teeth present, connected by faint U-shaped carina (Fig. 8A). Ventral transverse longitudinal carina fully developed, with median notch ( Figs 7A View Figure 7 , 8A View Figure 8 ). Antennomeres 4 and 5 combined approximately the same length as antennomere 6, maxillary palp elongate, five-segmented (Fig. 8B). Fore coxa expanded medially. Median mesoscutal sulcus and notauli at most weakly developed, mesoscutellum triangular, acute, raised compared to surrounding sclerites (Fig. 6A, B). Forewing vein 1r arises from approximately middle of pterostigma; vein 1r-Rs well developed, elongate, discal cell trapezoid, proximal part broader than distal part (Fig. 6A).

Description: Female ( Figs 6 View Figure 6 , 7 View Figure 7 ). Body length 3. 8 mm. Original body coloration not observable. Specimen very well preserved and well observable from most angles except for distal margin of right forewing, which is obscured by narrow cracks extending from the wings. Forewings folded above abdomen, obscuring it and the hindwings in dorsal view.

Head: Ocellar corona narrow, distance between median ocellus and lateral coronal tooth less than ocellar width; ventral coronal teeth present, situated slightly medial to median coronal teeth; faint median frontal carinae extend ventrally from ventral coronal teeth and converge medially, forming U-shaped loop (Fig. 8A). Dorsal transverse and longitudinal frontal carinae absent. Ventral transverse frontal carina continuous medially and with slight incision, covering toruli in anterior view (Fig. 8A); carina laterally continuous with lateral carina of subantennal groove (Fig. 7). Frons and vertex areolate (Fig. 8A), genae with scattered punctures; frons, vertex, and genae without conspicuous pilosity. Postocular carina well developed for most of height of eye, occipital carinae present (Fig. 8B), continuous with distinct lateral carina of subantennal groove ventrally. Tentorium with median lamellae on anterior arm broadening posteriorly (Fig. 8E, F), lateral lamellae hardly developed; tentorial bridge narrow, arched, with distinct anterior process (Fig. 8F); dorsal tentorial arms arise posteriorly on anterior arms, short, apparently do not reach head capsule (Fig. 8C, D). Antennae with 10 antennomeres, covered with short hairs; scapus short, subcylindrical (Fig. 8A); combined length of antennomeres 4 and 5 approximately equal to antennomere 6; antennomere 9 longer than antennomeres 7 and 8 combined, swollen subapically, without carina laterally; antennomere 10 short, cylindrical, inserted subapically on antennomere 9 (Fig. 7). Labrum visible between mandibles ( Figs 7A View Figure 7 , 8A View Figure 8 ), small, globose, with distinct ventrally directed hairs. Mandibles chisel-like, no teeth developed, with conspicuous distally pointing hairs laterally. Maxillary palps elongate, five-segmented, labial palps short, three-segmented (Fig. 8B); glossa of labium folded longitudinally, concave in posterior view.

Thorax: Pronotum dorsally short, of equal length throughout, deeply incurved posteriorly (Fig. 6B), laterally evenly punctured. Prosternum mostly concealed by propleura, diamondshaped, lateral margins diverging anteriorly, discrimen and discrimenal lamella distinct; profurcal arms extend obliquely anteriorly from posterior corners of prosternum, profurcal bridge low and straight, with distinct median groove accommodating lower branch of curved ovipositor (Fig. 9B), bridge not bent posteriorly. Fore coxa expanded medially; ventral carina on fore femur not observed; fore tibia swollen distally and subdivided by groove (Fig. 7); fore tarsus with three tarsomeres, basitarsus elongate and terminating in spur overlapping tarsomere 2. Mesoscutum finely punctate, not densely covered with hairs, median mesoscutal sulcus absent, notauli only developed as shallow grooves not reaching transscutal articulation posteriorly, parapsides present laterally and transscutal articulation posteriorly (Fig. 6); axillar flanges well developed; scutoscutellar sulcus well developed; mesoscutellum areolate-punctate, rounded triangular posteriorly (Fig. 6), raised and with smooth carinate lateral margins; mesoscutellar arms curved posteriorly, area anterior to arms raised to same level as arms; mesonotum continuous posterior to mesoscutellum. Mesopleuron areolate–punctate lateroventrally, mesosubalar carina present, mesepisternal carina absent; mid-coxa subdivided, with distinct lateral carina. Metanotum with median and lateral metanotal carinae well developed (Fig. 6B); metapleuron areolate across most of its surface; hind coxae not especially hairy laterally, with angled medioventral margin and well-developed posterolateral carina; ventral part of hind femur concealed; hind tibia with distinct pegs dorsally, longitudinal and ventral carinae not observed; apical hind tibial spurs short, of approximately equal length.

Wings: Forewing apparently without marked bands of infuscation; vein 2r-rs arise from approximately middle of pterostigma; vein 1-Rs well developed, elongate, discal cell trapezoid, proximal part higher than distal part (Fig. 6A); vein cu-a inserts on Cu1 only slightly distally to vein M. Hindwing venation cannot be observed.

Abdomen: Dorsally covered by wings, hence obscuring structural detail; laterally not particularly hairy, sculpture finely imbricate. Tergum 1 with weakly developed postspiracular carina, subspiracular carinae absent. Tergum 2 without median carina (Fig. 6B), with rectangular smooth area laterally abutting antecosta. Median apodemes observed on several abdominal sterna; sternum 7 externally with narrow median part delimited laterally and projecting posteriorly (Fig. 7A). Tergum 9 punctate, with low, longitudinal carinae delimiting concave depression medially, smooth areas and depressions absent. Tip of ovipositor slightly protruding from tip of abdomen, third valvulae exposed ventrally (Fig. 7A). Internally, complete ovipositor loop can be traced (Fig. 9D), loop simple, hairpin-like, anterior part of ventral branch runs through dorsal longitudinal groove of profurcal bridge (Fig. 9C); traces of ovipositor sack containing loop observed. Composite tergum 10/cercus triangular, not continuous medially.

Etymology: The species epithet honours Mrs Jutta Gröhn, wife of Carsten Gröhn and longterm supporter of his passion for amber insects.

Comments: † Orussus juttagroehnae displays a character combination that unequivocally places it in Orussus Latreille 1796 (see Diagnosis); this is corroborated by the phylogentic analyses (Fig. 10), which places the new species nested well inside Orussus , as sister to Orussus hanumanus Vilhelmsen and Blank 2014 . The RoguePlots (Supporting Information, Fig. S8) in a single instance places † O. juttagroehnae outside Orussus , but with low probability. A putative autapomorphy of Orussus that could not be confirmed in † O. juttagroehnae is the presence of white spots on at least some legs (Vilhelmsen 2003) and also on other body parts (e.g. face, antennae, pronotum, abdominal tip) in some species; given that the natural colour of the fossil specimen is not observable, white spots might well be present. † Orussus juttagroehnae can be separated from all other Orussus spp . by the unique U-shaped configuration of the short median frontal carinae and the comparatively well-developed vein 1-Rs in the forewing. † Orussus juttagroehnae is the first fossil species described from the genus, and the oldest member of an extant orussid genus recorded so far; † Ophrynopus peritus Engel 2008 is from the much younger Dominican amber.

The holotype of † O. juttagroehnae is also among the smallest specimens of Orussus spp . recorded; its body length of 3. 8 mm ties with Orussus minutus Middlekauff 1983 at the lower end of the size range for this genus; the upper limit observed by Vilhelmsen (2004: table 2) being 16.0 mm (e.g. Orussus abietinus Scopoli 1763 ). This is the more remarkable as the † O. juttagroehnae specimen is a female and females tend to be significantly larger than males; the smallest specimen of Orussus minutus measured by Vilhelmsen (2004) was a male. There is, of course, preservational bias favouring smaller insect fossils in amber, but † O. juttagroehnae is not the smallest orussid recorded. Among extant taxa, a female Orussobaius minutissimus Schmidt and Vilhelmsen 2002 is the smallest with a body length of 2.0 mm (see: Blank and Vilhelmsen 2016: fig. 11); among fossils, † Minyorussus luzzi Basibuyuk et al. 2000 (male, 2. 2 mm) and possibly † Mesorussus taimyrensis Rasnitsyn 1977 [female, possibly 1.75 mm—body length of incomplete fossil estimated by Vilhelmsen (2004)] are the smallest recorded.