Groehnaltica Bukejs, Reid and Biondi, 2020

Bukejs, Andris, Reid, Chris A. M. & Biondi, Maurizio, 2020, Groehnaltica batophiloides, a new genus and species of flea-beetles (Coleoptera Chrysomelidae) from Baltic amber, described using X-ray microtomography, Zootaxa 4859 (3), pp. 397-408 : 398-403

Groehnaltica Bukejs, Reid and Biondi , gen. nov.

( Figs 1–17 ; Appendices 1–4) http://zoobank.org/ urn:lsid:zoobank.org:act:5EC16C11-6DAF-4D53-8EA0-D8832F51940F

Type species: Groehnaltica batophiloides Bukejs, Reid and Biondi , sp. nov. by present designation

Description. Small, elongate-ovate, length 2× greatest width; elytra slightly rounded at sides, widest at middle, width at humeri about 1.3× width pronotum and about 1.6× width head. Dorsal punctures generally large but sparse and shallow. Dorsum mostly glabrous, except patches of short setae at sides and anterior of head, a pair of trichobothria at anterior of vertex, a trichobothrium at each corner of pronotum and about 3 distinct setae on lateral pronotal margins between trichobothria; elytra without discal setae. Thoracic and abdominal venter mostly impunctate and apparently mostly glabrous.

Head. Face with strongly convex profile, abruptly excavated before anterior edge of clypeus; eyes large, later- ally prominent, with straight or feebly concave inner margins, separated by less than eye length but more than eye width; ommatidia convex with minute setae between; vertex medially smooth, without median groove, laterally bounded by deep supraorbital (ocular) sulci which arise at posterior margins of antennal sockets and curve obliquely to posterior of eyes; orbit flat between eye and frontal calli, less than half as wide as antennal socket; frons with pair of lanceolate frontal calli, defined by laterocallar (ocular) sulcus anteriorly, feebly defined posteriorly, widely separated by a median depression; frontoclypeal median ridge prominent, narrow-linear, from middle of antennal sockets almost to anterior edge of clypeus; lateral margins of frontoclypeal area, anterior to antennal sockets, not elevated; interantennal space 0.8–1× socket diameter (sockets asymmetric), sockets approximately level with middle of eyes and separated from them by 0.3–0.5× socket diameters, antennal socket entirely defined by a raised ridge; antenna 11-segmented, length about 0.7× body length; all antennomeres elongate, scape ≤1.5× length pedicel, pedicel slightly longer and much wider than antennomere 3, antennomere 3 shortest, antennomere 11 longest, not apically expanded; labrum with 3 pairs of discal setae, apical margin truncate; apical maxillary palpomere elongate-conical, longer than and as wide as preapical; gena 0.2× or less eye length (eyes asymmetric in size), without transverse setose ridge between eye and buccal cavity.

Thorax. Prothorax distinctly broader than head and narrower than elytra (about 0.8× width elytra at humeri), widest at middle, sides of pronotum convex; pronotal disc evenly convex; with two large, probably glandular, punctures at lateral margins; pronotum feebly transversely depressed anterior to basal margin, depression not defined laterally, without two short longitudinal grooves; anterior and posterior angles each with trichobothrium, anterior angles rounded, with distinctly swollen pronotal callus, anterior trichobothria inserted on posterior of callus, posterior angles slightly projecting laterally; pronotum with thick raised border present laterally, raised border absent or thin and feebly developed at base (not clear), absent anteriorly; hypomeron without groove near lateral margins; prosternal process slightly convex, elongate, slightly expanded beyond procoxae, transversely grooved at base; procoxal cavities broadly open, gap greater than length of hypomeral process; scutellum semi-ovate; elytra strongly convex in cross-section, covering abdomen, subparallel-sided in basal half, rounded in apical half, with distinct humeri, and nine distinct regularly punctured striae on disc, tenth stria along upper margin of epipleuron and distinct punctate striole about one third of elytral length, without transverse posthumeral depression; epipleuron distinct, entirely laterally visible, gradually narrowed from base to apex, with upper margin open, not fusing with lower margin at elytral apex; fully winged; mesoventrite not covered by metaventrite, with single arcuate cavity at anterior edge (procoxal rest); mesoventrite process exposed, approximately quadrate, apex truncate with narrow projecting lobes at lateral angles; mesocoxae separated by about half width of mesocoxa; middle of metaventrite slightly swollen posteriorly; pro- and mesofemora narrowly fusiform, metafemur much larger, greatest width in basal half, more than twice width mesofemur, dorsal margin strongly convex, ventral margin weakly convex, without distinct keel; tibiae without apical excavation on outer edge; protibia not expanded to apex; metatibia not prolonged beyond tarsal insertion (insertion apical), curved in lateral view with ventral face convex, apically expanded and flattened dorsally, with row of spines on outer edge and possibly thickened spiniform setae on either side of apex; pro- and mesotibiae without apical spurs, metatibia with small conical apical spur, inserted on outer side of apex, about half apical tibial width or less; length metatarsus about 0.8× length metatibia; metatarsomere 1 long, about 0.4× metatibia, longer than metatarsomeres 2–5 combined; tarsomere 3 deeply bilobed; apical metatarsomere not arched or inflated; tarsal claws appendiculate, appendage slightly less than right-angled, more than half claw length.

Abdomen. Pygidium rounded at apex, without longitudinal median sharp edged groove; abdominal ventrites free, not fused; surface ventrite 1 evenly convex, without median ridges, intercoxal process broadly triangular; ventrites 1–5 laterally bordered; male ventrite 5 with median flat lobe, apex convex; median lobe of aedeagus symmetrical, apex entire, base without recurved lobes, dorsum with small transverse foramen, venter probably mostly membranous (cuticle absent); tegmen unknown; female genitalia unknown.

Comparison. This new fossil genus differs from other flea-beetles described from Eocene fossil resins in hav- ing the combination of the following characters: frontal calli lanceolate, rather wide and separated by a broad groove at midline; pronotum without antebasal transverse impression, and without short sublateral longitudinal impressions; elytral punctation large and close, arranged in regular striae; metafemora strongly swollen, about 1.8× as long as wide; metatibiae with small spines dorsolaterally in apical portion; metatarsi attached to apices of metatibiae; metatarsomere 1 moderately long, nearly as long as metatarsomeres 2–4 combined; tarsal claws appendiculate; and small body size (1.7 mm).

Amongst extant European genera, Groehnaltica is similar to Batophila Foudras, 1859 , a flea beetle genus widespread in the Palaearctic. The similarities include: small size, postantennal tubercles weak or not distinguish- able, strongly punctured pronotum, pronotum without either well defined antebasal transverse impression or short longitudinal grooves; strongly punctured elytral striae with convex intervals, procoxal cavities broadly open, metatibia flattened apicodorsally with thickened setae on apex of outer margin, third tarsomere bilobed, and tarsal claws appendiculate. However, Batophila species are flightless and have typical features of loss of flight which are absent from this fossil: scutellum reduced, elytra rounded without humeri, and metaventrite foreshortened. In addition, Groehnaltica is easily distinguishable from Batophila because it possesses the following characters: postocular sulci present (absent in Batophila ); distal antennomeres elongate, at least twice as long as wide and not expanded apically (triangular to subglobose in Batophila ); epipleural upper margin open, not fused with lower margin at or before apex (fused in Batophila ); metatibiae robust, slightly curved and with small spines dorsolaterally in apical portion (slender, straight and without evident spines in Batophila ); male protarsomere 1 distinctly dilated and suboval (not dilated, subtriangular in Batophila ). Furthermore, in Batophila species with distinct postantennal tubercles, these are anteriorly elongately pointed and juxtaposed, reaching between the antennal sockets (e.g. in B. acutangula Heikertinger, 1921 ). The unusual and possibly unique lateral pronotal pits on Groehnaltica may also be a diagnostic generic attibute.

Groehnaltica is also similar to several Asian genera which have been identified as possibly monophyletic ( Ruan et al. 2019), particularly Bikasha Maulik, 1931 (distributed in Asia, Australasia and the Afrotropics) and Lanka Maulik, 1926 (distributed in Asia). With Bikasha and Lanka¸ the new fossil genus shares similar eye shape, postocular grooves, narrow frontoclypeal ridge, elongate antennomeres, thickened pedicel, shape of pronotum and prosternum, punctate elytral striae, open-ended epipleuron, deep punctures on margins of pterothoracic sclerites, swollen posterior of metaventrite, strongly inflated metafemur, elongate metatarsomere 1, and claw shape ( Konstantinov & Prathapan 2008; Ruan et al. 2019). Furthermore, Bikasha has a small body (1.5–2.5 mm), and the outer margin of metatibia with a row of small spinules. However, both Bikasha and Lanka have undivided tarsomere 3, Bikasha has well-defined postantennal calli with the postocular groove poorly developed, and Lanka has paired ridges on the intercoxal process of abdominal ventrite 1 (note that the type species of Bikasha lacks these, despite statements to the contrary). In contrast, the new fossil genus has plesiomorphic attributes of the bilobed tarsomere 3 and simple unridged abdominal ventrite 1, which may indicate its relationship to these extant palaeotropical genera.

Etymology. The name of this new fossil genus consists of two parts: the first is dedicated to Carsten Gröhn (Glinde, Germany), who provided the specimen for examination, and the second - the name of the extant genus Altica Geoffroy, 1762 . Gender feminine.

Figures

FIGURES 1–3. Photomicrographs of Groehnaltica batophiloides holotype, C 7806 [GPIH]: 1—habitus, left lateral view; 2— habitus right lateral view; 3—right metatibia and metatarsus, lateral view. Scale bars represent: 0.4 mm for Figs. 1 and 2; 0.2 mm for Fig. 3.

FIGURES 4–7. X-ray μCT renderings of Groehnaltica batophiloides holotype, C 7806 [GPIH], habitus: 4—right lateral view; 5—dorsal view; 6—left lateral view; 7—caudal view. Scale bar represents 0.4 mm.

FIGURES 8–9. X-ray μCT renderings of Groehnaltica batophiloides holotype, C 7806 [GPIH], habitus: 8—ventral view; 9—ventral view without legs, showing details of thorax and abdomen. Scale bar represents 0.4 mm.

FIGURES 10–13. X-ray μCT renderings of Groehnaltica batophiloides holotype, C 7806 [GPIH], details of head and prothorax: 10—dorsal view; 11—ventral view; 12—frontal view; 13—right lateral view.Abbreviations: as—antennal socket, c—clypeus, fcl—postantennal callus, fcr—frontoclypeal carina, la—labrum, m—mandible, mp3–mp4—maxillary palpomeres 3 and 4 respectively, o—orbit, os—orbital sulcus, p—prosternal intercoxal process, pc—procoxa, scs—supracallar sulcus, sos—supraorbital sulcus. Scale bar represents 0.4 mm.

FIGURES 14–17. X-ray μCT renderings of Groehnaltica batophiloides holotype, C 7806 [GPIH], aedeagus: 14—dorsal view; 15—ventral view; 16—lateral view; 17—ventro-lateral view.