Eoidiocerus, Dietrich, Christopher H. & Thomas, M. Jared, 2018

Dietrich, Christopher H. & Thomas, M. Jared, 2018, New eurymeline leafhoppers (Hemiptera, Cicadellidae, Eurymelinae) from Eocene Baltic amber with notes on other fossil Cicadellidae, ZooKeys 726, pp. 131-143 : 132-134

Eoidiocerus gen. n.

Type species.

Eoidiocerus emarginatus sp. n.; by present designation and monotypy.

Diagnosis.

This genus differs from other described genera of Idiocerini in having the following combination of traits: head with fine arcuate striations above ocelli, ocelli situated above mid-height of eye, gena strongly emarginate below eye; hind femur macrosetal formula 2+1; female abdominal sternite VII strongly emarginate, exposing base of ovipositor; length of ovipositor more than half that of entire abdomen.

Description.

Head in dorsal view with crown slightly shorter medially than next to eyes; face slightly longer than width across eyes, texture shagreen, area of vertex above ocelli with inconspicuous, fine arcuate parallel striations; ocelli approximately equidistant between eyes and midline, situated above mid-height of eyes; lateral frontal suture nearly straight, extended from antennal pit to ocellus; antennal ledge carinate but only weakly produced over antennal base; antenna shorter than head width, arista attenuate, with conspicuous preapical seta extended mesad; gena strongly concave and narrow below eye, partly exposing small proepisternum; lorum convex, extended nearly to lateral margin of face; anteclypeus broadened near apex; rostrum extended slightly past middle coxae, distal segment somewhat expanded toward apex. Pronotum shagreen, with indistinct transverse rugae. Forewing elongate, appendix broad, extended to wing apex, bordering first and second apical cells; vein R with three branches extended to wing margin; crossvein s absent; with two r-m and three m-cu crossveins (two closed subapical cells); vein CuA reaching submarginal vein near midlength of appendix; claval veins distinct. Front femur with AM1 strongly reduced; intercalary row with several long, fine setae; tibia cylindrical, with conspicuous setae only at apex. Middle femur and tibia without macrosetae. Hind femur macrosetal formula 2+1; tibia strongly flattened, distance between dorsal setal rows much less than distance between dorsal and ventral rows, row AD with fewer macrosetae than PD, row AV macrosetae distributed along distal 3/4 of tibia, row PV with alternating short and long tapered setae through most of length, tarsomere I with dorsoapical pair of macrosetae well developed, without plantar setae, pecten with 2 platellae. Female pygofer and ovipositor narrow and elongate, occupying 3/4 total length of abdomen; sternite VII with deep median parabolic emargination, exposing base of ovipositor.

Etymology.

The genus name, a masculine noun, combines the Greek word eos (dawn) with Idiocerus , the name of the type genus of Idiocerini , referring to the status of the fossil as the oldest known representative of Idiocerini ..

Notes.

Placement of Eoidiocerus in Idiocerini is unequivocal and supported by the presence of several synapomorphic features diagnostic for that tribe, including: head broader than pronotum, crown short, ocelli on face distant from dorsal margin and well separated from eyes, lateral frontal sutures present and extended to ocelli; pronotum in dorsal view with anterior margin not extended anteriad of eyes; chaetotaxy of front and middle legs strongly reduced; forewing appendix broad and extended to wing apex. Eoidiocerus resembles several modern idiocerines in most external structural features. Its most distinctive diagnostic traits are the arcuate series of fine striations on the vertex above the ocelli, present in several modern genera (e.g., Idiocerus Lewis, 1834, Idioceroides Matsumura, 1912; see also Webb 1983b), the relatively long and narrow face (occurring also in some Paleotropical genera, e.g., Chunra Distant, 1908), the distinctly emarginate, relatively narrow gena (broad and not, or very weakly, emarginate in most modern idiocerines), and the greatly elongated female pygofer and ovipositor, which occurs also in some modern species of Idiocerus . The forewing venation of the only available specimen is poorly delimited but the visible parts suggest that the venational pattern in this genus is similar to that exhibited by most modern genera of the tribe, i.e., only two closed anteapical cells are present and the appendix borders only two apical cells rather than three as in some genera from South Asia and Madagascar ( Viraktamath 2007, Krishnankutty and Dietrich 2011). In the structure and proportions of the head, pronotum and mes onotum, the new genus is perhaps most similar to Cafixia Webb, 1983b, a genus represented by a single species occurring in South Africa, but Eoidiocerus differs in having the gena distinctly emarginate below the eye and exposing the small, flaplike proepisternum. Modern idiocerine genera known to have the gena distinctly emarginate below the eyes are Idioceroides from East Asia, and Tumocerus Evans, 1941 and Quilopsus Webb, 1983a from western Australia. Idioceroides differs in having the ocelli relatively high and laterad on the face and the lateral frontal sutures reduced. Tumocerus and Quilopsus differ in numerous respects, including having the face much wider than long, the lateral frontal sutures nearly vertical in orientation, and the portion of the vertex dorsad of the ocelli relatively short and lacking arcuate striations ( Webb 1983a: figs 449, 464). The emarginate gena of Eoidiocerus also approaches the condition found in Macropsini , but in that tribe the gena is even more strongly emarginate, the proepisternum is enlarged and the lateral frontal sutures are poorly delimited or absent and not extended to the ocelli.

Previously reported fossil Idiocerini include Oligoidiocerus pronotumnalis Statz, 1950, Idiocerus goeckii Statz, 1950 and an additional unnamed " Idiocerus ?" species from the Oligocene of Germany ( Statz 1950). Oligoidiocerus apparently lacks an appendix in the forewing ( Statz 1950: fig. 17) and, therefore, probably does not belong to this tribe. Its forewing venation is consistent with that of tribe Macropsini but other characters that could confirm its placement in that tribe do not appear to be visible on the fossil ( Statz 1950: fig. 58). Idiocerus goeckii has the forewing venation well preserved and resembling that of modern species of Idiocerus ( Statz 1950: fig. 18), differing from Eoidiocerus in the apparent lack of vein R1 and crossvein m-cu2. According to the photograph provided by Statz (1950: fig. 59) the specimen he identified as " Idiocerus ? sp." is too poorly preserved to confirm its placement in Idiocerini .