MIDDLE JURASSIC NANNOCHORISTIDAE FOSSILS FROM DAOHUGOU,INNER MONGOLIA IN CHINA(INSECTA,MECOPTERA)

Abstract

In this article,one new genus and two new species were described.All of them were collected from the Middle Jurassic Jiulongshan Formation of Inner Mongolia in China and deposited in the Capital Normal University.The origin and evolution of Nannochoristidae are discussed briefly.Protochoristella gen.nov.Type species.Protochoristella polyneura sp.nov.Diagnosis.Small insect,rostrum short and slender.The forewing pterostigma clearly present.Sc long,2-branched,reaching the pterostigmal region.R_1 not branched,Rs 4-branched,forking earlier than M.M 4-branched,CuA and M fused for a long distance,cubito-median Y-vein existent.2 cross-veins between CuA and CuP present.The hindwing Sc a little shorter.CuA coalesced with M basally for a short distance.Comparison.At present,two extant and six extinct genera have been reported(Novkoshonov,1997).In the general venation scheme the Protochoristella gen.nov.somewhat resembles Itaphlebia(Sukatcheva,1985),but the new genus differs from the latter by R_1 not branched,both Rs and M forking early,the cross-vein between 1A and CuP absent.The new genus also may be distinguished from other seven known genera by Rs 4-banched.Etymology.The genus name is a combination of proto-(Greek,meaning original)and choristella(one recent genus of this family).Protochoristella polyneura sp.nov.Etymology.Polyneura from Latin,means complex veins in the wing.Holotype.A well preserved female insect.Registration No:CNU-M-NN-2006049.Locality and horizon.Daohugou Village,Ningcheng County,Inner Mongolia,China;Jiulongshan Formation,Middle Jurassic.Description.Small insect, 6.5?mm long.Wings almost symmetrically arranged,with a pair on each side.Both the fore and hind wings are clear.The rostrum short and slender,maxillary palp 4-segmented.Antennae filiform,incomplete,visible more than 30 segments. Pro-and metathorax small,mesothorax well developed.Legs slender,covered with dense and tiny setae,irregular arrangement.Tarsi longer than others,5-segmented,basitarsus longer than the sum of others,the pretarsus with 2 terminal claws.Abdomen with 10 visible segments,basitergum fused to metathorax,shorted.At the apex of the abdomen is a pair of 2-segmented cerci.Forewing slender, 7.5?mm long, 2?mm wide,the base much narrower,apical margin rounded.Pterostigma clearly present.Sc long,2-branched,reaching the pterostigmal region.R_1 simple,not branched,reaching the wing margin,curving posteriorly near its termination.Rs arising from the base,4-branched,dividing into its two main branches nearly midwing,R_ 4+5 forking early,R_ 2+3 simple.M 4-branched,M_ 3+4 forking before M_ 1+2 ,which forks after the forking of R_ 4+5 .CuA coalesced with M for a long distance basally,M+CuA fused to R for a short distance before the forking.CuP simple,2 cross-veins between CuA and CuP exist.1A and 2A simple,but 2 cross-veins between them present.The hindwing smaller than forewing,but slightly broader and Sc a little shorter.CuA coalesced with M basally for a short distance.The cross-veins between CuA and M_ 3+4 ,CuP and CuA absent.2A not preserved.Other veins are similar to the forewing.Protochoristella formosa sp.nov.Etymology.Formosa from Latin,means beautiful.Holotype.A well preserved female insect,part and counterpart.Registration No:CNU-M-NN-2006006.Locality and horizon.Daohugou Village,Ningcheng County,Inner Mongolia,China,Jiulongshan Formation.Middle Jurassic.Description.Small insect, 7?mm long.Wings almost symmetrically arranged,with a pair on each side slightly overlapped,the veins of fore wings are clear,but hindwings not discernible.Vertex of the head not raised,the rostrum incomplete,maxillary palp 4-segmented,eyes distinct.Antennae filiform,incomplete,visible about 30 segments.Pro-and metathorax small,mesothorax well developed.Legs slender,covered with dense and tiny setae,irregular arrangement.Tibiae long,visible 1 terminal calcar.Tarsi 5-segmented,basitarsus longest,the pretarsus with 2 terminal claws.Abdomen with 10 visible segments,basitergum fused to metathorax,shorted,9 and 10 segments abruptly more slender than 2-8,at the apex of the abdomen is a pair of 2-segmented cerci.Fore wing 8?mm long, 3?mm wide,basal space shrinked slightly,apical margin rounded.Pterostigma clearly present.Sc long,2-branched,reaching pterostigmal region.R_1 reaching the wing margin,curving posteriorly near its termination.Rs arising from the base,4-branched,forking before midwing,R_ 4+5 forking early,R_ 2+3 simple.M arising close to the base,4-branched,M_ 3+4 forking before M_ 1+2 ,which forks after the forking of R_ 4+5 .CuA coalesced with M for a long distance basally,with a slight bend after the cross-vein to M_ 3+4 .CuP clearly,separated from CuA,but joined to it by 2 short cross-veins.1A and 2A simple,cross-veins between them absent.The hindwing smaller than forewing,but slightly broader,veins not discernible.Comparison.The new species different from Protochoristella polyneura sp.nov.in the following features on the forewing:M+CuA not fused to R basally for a short distance,the cross-veins between 1A and 2A absent.