Three New Stoneflies (Insecta:Plecoptera) from the Yixian Formation of Liaoning,China

Three new genera and species Archaeoperla rarissimus gen.et sp.nov.(Perlidae), Liaotaenionema tenuitibia gen.et sp.nov.(Taeniopterygidae)and Parvinemoura parvus gen.et sp.nov. (?Nemouridae)are described and illustrated.All of them were collected from Yixian Formation of the western Liaoning,China.Hitherto,A.rarissimus is the oldest species possessing typical characters of Perlidae;the finding of L.tenuitibia indicates taeniopterygids once lived in the northeastern China in the late Mesozoic,but frequent volcanic activities,climate changes,or other environmental changes might have resulted in the disappearance of Taeniopterygidae in northern China after Mesozoic. Ancestral groups of Nemouridae have been abundant from Middle Jurassic,and male genitalia of P. parvus gen.et sp.nov.has been developed and similar to extant Nemouridae in the late Mesozoic.The stonefly fossils found from Yixian Formation are not divers at the species level,but rich at the family level.The diversity of stonefly implies different microclimate existed in the northeastern China at that time.A large old lacustrine basin existed in the western Liaoning,surrounded by hygrophilous plants on swampland and lake shore,warm and humid;tall arbor and boscage on the hillside nearby,mild and dry;mountains in the distance,rivulets running among the mountains,cool and wet.Many insects,prefer cool climate(e.g.stonefly,raphidiopterans,et al.),lived in the mountains with rivulets.