Largusoperla, 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 : 574

Genus Largusoperla gen. nov.

Type species. Largusoperla acus gen. et sp. nov., by monotypy.

Diagnosis. The new genus exhibits typical characters of the family Perlidae , such as the presence of slender palpi, thoracic gill remnants, euplantulae, short first tarsal segment, and the numerous crossveins in basal half of forewing’s costal field. Comparative morphological analysis concerning the terminalia structures and other habitus characters further confirms that no generic definition from extant Perlidae applies to the new genus. It can be distinguished from other genera of Perlidae by having the combination of the following characters: 1) triocellate; 2) head with dark stigma covering ocelli; 3) pronotum brown, rugose but median area pale; 4) abdominal terga with darker lateral markings; 5) abdominal segments posterolaterally extended; 6) paraprocts distinctly enlarged, usually upcurved and with various modifications apically; 7) sternum 9 with a small elevated lobe 8) cerci very short, no more than half-length of abdomen.

Etymology. The genus name is a combination of the words Larguso and perla ; the first Latin word means the specimens’ large paraprocts, while the second word refers to the extant genus Perla Geoffroy, 1762 , which is the type genus of Perlidae .

Remarks. The familial affiliation of the new genus as Perlidae is based on the following characters: slender and filiform of palpi, presence of thoracic gill remnants, short first tarsal segment, presence of euplantulae on first and second tarsal segments, and numerous crossveins in basal half of forewing’s costal field ( Zwick 1980, 2000, Nelson 2009). The family Perlidae contains two subfamiles, Perlinae and Acroneuriinae ( Zwick 1973, Stark & Gaufin 1976). The Perlinae has divided tergum 10 forming projected hemiterga and has reduced paraprocts ( Zwick 1980, 2000, Sivec et al. 1988). While in Acroneuriinae , the hemiterga are absent; the paraprocts are sclerotized and upcurved, usually with sharp apices ( Zwick 2000, Murányi & Li 2016). The absence of projected hemiterga ( Figs. 6 , 13 ), the well-developed paraprocts ( Figs. 5–7 , 12–13 , 19 ), and the hammer of sternum 9 ( Figs. 5 , 12 , 19 ) provide support for the new genus to be a member of the Acroneuriinae .

Three tribes are included in Acroneuriinae : Acroneuriini , which is distinguished by enlarged transverse epiproct and by the sternal hammer forming a low callus or absent; Kiotinini , which usually has one enlarged, valve-shaped proventricular fold in the nymphal gut; and Anacroneuriini , which has paired opposed sclerotized hooks and the hammer is a raised knob or absent ( Zwick 2000, Stark 2001, Murányi & Li 2016). Though the epiproct and aedeagus are invisible in the preserved specimens, the elevated lobe on sternum 9 ( Figs. 5 , 12 , 19 ) may suggest a tribal assignment to Anacroneuriini . The extant genera of Anacroneuriini usually have spinose patches on abdominal terga, with relatively small paraprocts and long cerci, and often with two ocelli (Stark 2001). However, the new genus has distinctly large paraprocts, short cerci, and three ocelli. Notably, most of Acroneuriini have short cerci and three ocelli. The new genus may be a stem group of Anacroneuriini + Acroneuriini .

Figures

FIGURES 1–7. Largusoperla acus sp. nov., holotype male. 1. HabituS, dorSal view; 2. ReconStruction of head and pronotum, dorSal view; 3. TarSal SegmentS of right hind leg; 4. Right forewing; 5. Terminalia and itS reconStruction, lateral view; 6. Terminalia and itS reconStruction, dorSal view; 7. Terminalia, dorSolateral view.

FIGURES 8–13. Largusoperla flata sp. nov., holotype male. 8. HabituS, dorSal view; 9. Head and pronotum, dorSal view; 10. TarSal SegmentS; 11. Right forewing; 12. Terminalia and itS reconStruction, ventral view; 13. Terminalia and itS reconStruction, dorSal view.

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.