Largusoperla arcus, Chen & Wang & Du, 2018

Chen, Zhi-Teng, Wang, Bo & Du, Yu-Zhou, 2018, Discovery of a new stonefly genus with three new species from mid-Cretaceous Burmese amber (Plecoptera: Perlidae), Zootaxa 4378 (4), pp. 573-580 : 577-579

Largusoperla arcus sp. nov.

( Figs. 14–19 )

Diagnosis. As for the genus, except for the apically sharp, sickle-shaped paraprocts.

Description. Macropterous; body length (excluding antennae and cerci) ca. 7.5 mm, arched in the amber; generally brown ( Fig. 14 ).

Head ( Figs. 14, 15 ): Head rounded and mostly brown, with paired bulging eyes and three ocelli, a dark stigma covering the three ocelli. Antennae brown, hairy and filiform, with up to 41 segments and apical segments thinner and longer than basal ones. The maxillary palps slender and much longer than the labial palps.

Pronotum ( Figs. 14–16 ). Pronotum slightly narrower than head, mostly brown except for the pale median band, near reverse trapezoidal in shape with obtuse corners, width longer than length. Mesothorax and metathorax sclerotized, length similar to prothorax; meso- and metathoracic gill remnants indistinguishable. Forelegs shortest, hindlegs longest; femur and tibia mostly brown except for the pale joints; tibia longer than femur, ventroapically with two slightly enlarged spurs; tarsi three-segmented, first two segments shortest, equal in size and with conspicuous euplantulae; claws simple, with sharp and dark apex.

Forewings ( Fig. 17 ). Wings length 7.9 mm, width 2.8 mm. ScP about three-fourth of total wing length, reaching ScP+RA beyond ra-rp; area between anterior margin and RA with one crossvein; 12–13 crossveins present between ScP and the anterior margin. RP originated near mid-RA and forked with two branches. M forked at apical one-third of the wing, with two branches in left forewing and three branches in right forewing. Right forewing with only one crossvein, but left forewing with two crossveins between RP and M. Cu forked to CuA and CuP, CuA forked basal to the fork of M and with three branches; CuP simple and near straight; area between M and CuA with five crossveins and about 1.5X wider than area between CuA and CuP, which also with five crossveins. AA1 simple, AA2 forked with two branches.

Hind wings ( Fig. 18 ). Left hind wing length 6.5 mm, width 2.6 mm. ScP reaches RA before ra-rp; area between anterior margin and ScP with two crossveins; fewer crossveins present between ScP+RA and the anterior margin. RP with an extra small apical branch; M with four branches; CuA with at least one branch; median and cubital crossveins much fewer than forewings; part of CuA, CuP and AA veins invisible.

Abdomen ( Fig. 19 ). Abdomen near half the length of the body, each segment with dark lateral marks and slightly extended posterolateral margins. Sternum 9 with a slightly elevated lobe. Tergum 10 seems cleft or with median membranous area, without projected hemiterga. Paraproct large, darkly sclerotized and upcurved, claw-like and out-curved from ventral view, gradually tapered to an unmodified, relatively sharp apex. Abdominal tip with a subuliform membranous structure beyond paraprocts. Cerci hairy and short gradually elongated and narrowed from base to apex, with 9 to 11 segments and each segment with clustered long setae.

Type material. Holotype male, NIGP167160. Right hind wing of this specimen is fused with the dorsal abdomen, and basal half of left hind wing is folded, so the hind wing veins are described based on apical half of left hind wing.

Etymology. The specific epithet means “arch” in Latin, which refers to the preserved arched body of the holotype.

Syninclusions. Plant fragments and a claw remnant of a bird or other animals.

Figures

FIGURES14–19. Largusoperlaarcus sp. nov., holotype male.14. HabituS, ventrolateral view; 15.ReconStruction ofhead and pronotum, dorSal view; 16. TarSal SegmentS; 17. ForewingS; 18. Right hind wing; 19. Terminalia and itS reconStruction, ventral view.