Fossils from the Middle Jurassic of China shed light on morphology of Choristopsychidae (Insecta, Mecoptera)

Abstract Choristopsychidae, established by Martynov in 1937 with a single isolated forewing, is a little known extinct family in Mecoptera. Since then, no new members of this enigmatic family have been described. Based on 23 well-preserved specimens with complete body and wings from the Middle Jurassic of northeastern China, we report one new genus and three new species of Choristopsychidae, two new species of the genus Choristopsyche Martynov, 1937: Choristopsyche perfecta sp. n. and Choristopsyche asticta sp. n.; one new species of Paristopsyche gen. n.: Paristopsyche angelineae sp. n.; and re-describe Choristopsyche tenuinervis Martynov, 1937. In addition, we emend the diagnoses of Choristopsychidae and Choristopsyche. Analyzing the forewing length/width ratios of representative species in Mecoptera, we confirm that choristopsychids have the lowest ratio of forewing length/width, meaning broadest forewings. These findings, the first fossil choristopsychids with well-preserved body structure and the first record of Choristopsychidae in China, shed light on the morphology of these taxa and broaden their distribution from Tajikistan to China, while increasing the diversity of Mesozoic Mecoptera in China.


Introduction
Choristopsychidae is a rather obscure extinct family in the Order Mecoptera. The family, erected by Martynov in 1937 with an isolated forewing fossil, contains only one species up to date, Choristopsyche tenuinervis. Its locality is Shurab II Ditch 63(8), which is in a Pliensbachian terrestrial horizon in the Sulyukta Formation of Tajikistan (Lower Jurassic) (Martynov 1937, Aristov et al. 2009). The family is recognized by a combination of the following characters: forewing broad, ScP long with two long anterior branches; RP and MA with two branches each; MP with five branches; and CuA coalesced with MP basally, strongly bent at about its midpoint (Martynov 1937).
Recently, we collected 23 well-preserved fossils from the Daohugou Village, Ningcheng County, Inner Mongolia, China; Jiulongshan Formation, Middle Jurassic. Herein, based on their different morphological characters, we erect one new genus with one new species and two new species of Choristopsyche Martynov, 1937, and re-describe C. tenuinervis Martynov, 1937, while emending diagnoses of Choristopsychidae Martynov, 1937 andChoristopsyche Martynov, 1937. There are abundant well-preserved fossil insects from Daohugou, including 19 reported orders so far (Ren et al. 2010b). The age of the Daohugou fossil-bearing beds is ca. 164-165 million years ago (Ma) (Bathonian-Callovian boundary interval, the late Middle Jurassic) (Chen et al. 2004).

Material and methods
This study is based on 23 fossil specimens housed in the fossil insect collection of the Key Laboratory of Insect Evolution & Environmental Changes, College of Life Sciences, Capital Normal University, Beijing, China (CNUB; Dong Ren, Curator).
Photographs of whole specimens were taken with a Nikon D100 digital camera coupled to a Nikkor 105 mm macro lens. The specimens were examined using a Leica MZ12.5 dissecting microscope, and illustrated with the aid of a drawing tube attached to the microscope. Line drawings were made with CoreDRAW X4 graphic software.
The wing venation nomenclature used in this paper is based on the interpretations and system proposed by Novokshonov (2002) with some revisions, Corresponding abbreviations are: ScP, posterior Subcosta; RA, anterior Radius; RP, posterior Radius; MA, anterior Media; MP, posterior Media; CuA, anterior Cubitus; CuP, posterior Cubitus; 1A, the first anal vein; 2A, the second anal vein (Fig. 1E). The length of the wing is measured by the straight-line distance from the wing base to apex, and the width of the wing, the straightline distance from the wing anterior margin to posterior margin at its broadest point.
wings, but partially preserved hind wings and body, and forewings overlapping hind wings. The terminus of abdomen is missing, sex unknown. Wings: Left forewing, length 11.0 mm, width 6.7 mm, broadly oval, RP forking distal to MA forking; MP 2+3 forking basal to the forking of MA, and the stem of MP 3 about twice as long as the stem of MP 2+3 ; with one crossvein between RA and RP, and between MP 2+3 and MP 4 ; CuP, 1A, 2A single. Right forewing is similar to left forewing, but parts missing. Hind wings, smaller than forewings, overlapped by forewings, the venation visible but unclear. There are many spots on all four wings, symmetric between left and right wings.
In addition, there are nine new materials with analogous wing venation to that of specimen CNU-MEC-NN2011075p/c. They are listed as follows.
CNU-MEC-NN2011080 (Figs 2A, C), a well preserved specimen with clear wings, but parts of body, and the right forewing overlapping the right hind wing. Sex unknown. Wing: Right forewing, length 11.8 mm, width 6.7 mm, RP forking distal to the forking of MA; MP 2+3 forking at about the same level as the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 ; with one crossvein between MP 2+3 and MP 4 ; CuP, 1A, 2A single. Left forewing is similar to right forewing, but the apex of the wing absent. Hind wings, length at about 10.1 mm, width 6.2 mm, similar to forewings but smaller. CNU-MEC-NN2009317 (Figs 2B, D), an almost complete specimen, female, with forewings overlapping hind wings, and nearly complete body, but legs absent in dorsal view. Wings: right forewing, length at about 9.5 mm, width 4.9 mm; RP forking distal to the forking of MA; MP 2+3 forking at about the same level to the forking of MA; the stem of MP 3 as long as the stem of MP 2+3 ; CuP, 1A, 2A single. Left forewing is similar to right forewing. Hind wings, similar to forewings, but smaller; CuA almost straight. CNU-MEC-NN2009414 (Figs 2E, F), an almost complete preserved specimen in lateral view, female, with complete body and forewings, and right forewing overlapped with body and parts of left forewing, and right hind wing overlapped with left hind wing. The mouthparts are missing, the maxillary palpus with five segments visible. Abdomen: tapering apically, with eleven segments, and a pair of cercus can be visible, female. Wings: Left forewing, length at about 10.1 mm, width 6.4 mm, broadly oval, RP forking basal to the forking of MA; MP 2+3 forking significantly basal to the forking of MA; the stem of MP 3 about three times as long as the stem of MP 2+3 ; with one crossvein between RA and RP, and between MA and MP 1 ; CuP, 1A, 2A single. Right forewing is similar to left forewing, but there are crossveins between ScP and RA, RA and RP, MA and MP 1 . Hind wing: similar to forewing but smaller, RA straight, with one crossvein to RP. CNU-MEC-NN2009318 (Fig. 2G), a partially preserved specimen in dorsal view, with parts of forewings, hind wings and body, but the filiform antennae and venation visible, and the forewings overlapping the hind wings. CNU-MEC-NN2011070 (Fig. 2H), an almost completely preserved specimen in ventral view, with almost complete body and four wings, and hind wings overlapped with forewings. CNU-MEC-NN2011071 (Fig. 2I), a partially preserved specimen in dorsal view, with parts of body and forewings, but left hind wing is missing, and right hind wing is obscure. CNU-MEC-NN2009383 (Fig. 2J), a partially preserved specimen with four outspread wings and parts of body. CNU-MEC-NN2011083 (Fig. 2K), a specimen in dorsal view, female, with almost complete body but some legs not visible due to coverage by wings, and forewings overlapping hind wings. CNU-MEC-NN2011085 (Fig. 2L), a comparatively complete specimen in lat- eral view, male, and forewings overlapping hind wings; chewing mouthparts visible; Abdomen almost completely-preserved, the posterior six segments can be seen clearly, and abdomen bent at six and seven segment, but the posterior segments faint below the left forewing, the scorpion-like terminal visible.
New material.
Remarks. These ten specimens exhibit differences in the characters of "RP forking vs. MA forking", "MP 2+3 forking vs. MA forking" and "Length ratio of the stem of MP 3 and the stem of MP 2+3 " , which are considered as intraspecific variations.
Description. Holotype CNU-MEC-NN2011082 (Figs 3A, B), an almost complete preserved specimen, maybe male, with four outspread wings, but with partially preserved body. Head is partially preserved, only with one compound eye visible. Thorax: prothorax smaller than mesothorax and metathorax in ventral view. Legs: some parts of fore legs and left hind leg visible. Abdomen: tapering apically, with six segments visible, but the terminal visible, maybe male. Wings: Right forewing, length 22.2 mm, width at about 11.4 mm, RP forking distal to the forking of MA; MP 2+3 forking distal to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 ; with one crossvein between CuP and 1A; CuP, 1A single. Left forewing is partially preserved, similar to right forewing. Hind wings, length 18.4 mm, width at about 10.3 mm, similar to forewings but smaller than forewings, and left hind wing partially preserved. There are many spots on all four wings, symmetric between left and right wings.
Paratypes: CNU-MEC-NN2009352 (Figs 3C, E), an almost complete preserved specimen, with clear wing venation and structure of body in side pressure, and forewings partially overlapped with hind wings, sex unknown. Wings: Left forewing, length 18.8 mm, width 10.0 mm, RP forking slightly distal to the forking of MA; MP 2+3 forking at about the same level to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 ; with one crossvein between MP 1 and MA 4 , MP 1 and MP 2 , MP 2+3 and MP 4 ; CuP, 1A, 2A, 3A single, and one crossvein between CuP and 1A. Right forewing is similar to left forewing. Hind wing, similar to forewing, but smaller. CNU-MEC-NN2011079 (Fig. 3D), female, a well-preserved specimen with complete body, and the terminal of abdomen visible, but the end of legs absent, and forewings overlapping hind wings, but parts of wings missing, RP forking distal to the forking of MA; Abdomen: tapering apically, with eleven visible segments, the tenth and eleventh segments smaller, and the eleventh segment with cerci visible. CNU-MEC-NN2011084 (Fig. 3F), a specimen with legs absent, and hind wings overlapped by forewings in dorsal view, sex unknown. Forewing, length 19.4 mm, width 10.0 mm, RP forking at the same level to the forking of MA; MP 2+3 forking basal to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 .
Etymology. The name is derived from the Latin word of perfectus, meaning "complete". Remarks. These four specimens exhibit differences in the character of "RP forking vs. MA forking", "MP 2+3 forking vs. MA forking", which is considered as intraspecific variations.
Description. Holotype, CNU-MEC-NN2009394p/c (Figs 4A-D), an almost complete specimen, female, with well-preserved four outspread wings. Head: compound eyes are big and oval in ventral view, but mouthparts invisible and antenna partially preserved. Thorax: prothorax smaller than mesothorax and metathorax, visible in ventral view. Legs: all legs nearly the same shape and nearly completely preserved, long and slender in ventral view. Abdomen: slender and elongate, tapering apically, with eight visible segments. Wings: four wings are elongated and broad, with rounded apical margin. Forewings: Right forewing, length 20.7 mm, width 10.2 mm, almost triangular, dark color between C and RA; RP forking basal to the forking of MA; MP 2+3 forking at about the same level to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 ; the stem of MA strongly bent posteriorly; and the stem of MP 2+3 strongly bent at its basal one third part; with one crossvein between MA and MP 1 , MP 1 and MP 2 , and between MP 2+3 and MP 4 ; and one oblique crossvein between the base of CuA and CuP, and at the point one oblique crossvein between CuP and 1A, CuP, 1A, 2A single. Left forewing is similar to right forewing. Hind wings: similar to forewing, but slightly smaller, length at about 16.8 mm, width at about 10.0 mm; Right hind wing, with one crossvein between RA and RP+MA. Left hind wing is similar to right hind wing. No spots on entire wings.
Paratypes: CNU-MEC-NN2011081 (Fig. 4E), female, a well-preserved specimen, with complete body and wings; Head, oval with two big compound eyes, filiform antenna and chewing mouthparts; Abdomen, slender and elongate in lateral view, tapering apically and complete preserved, length at about 13.4 mm; Wings, forewings overlapping some parts of hind wings, and with clear venation; Forewing, length 19.8 mm, width 8.4 mm, RP forking basal to the forking of MA; MP 2+3 forking at the same level to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 . Hind wing, length at about 16.6 mm, width 8.1 mm. CNU-MEC-NN2011086 (Fig. 4F) Included species. Type species: Paristopsyche angelineae sp. n.. Etymology. The name is derived from the Greek word of paris-, meaning "equal", and psyche, from the Greek, meaning "soul" or "mind". The gender is feminine.
Description. Holotype, CNU-MEC-NN2011076p/c (Figs 5A-D), a well preserved specimen in dorsal view, with outspread clear wings, but parts of body visible. Some segments of head, thorax, legs visible, but faint. Wings: Right forewing, length 8.4 mm, width 5.5 mm, broadly oval with clear venation, RP forking distal to MA forking; MP 2+3 forking at about the same level of the forking of MA; the stem of MP 3 about three times as long as the stem of MP 2+3 ; with one crossvein between MA and MP 1+2+3 , and between MP 2+3 and MP 4 . Left forewing is similar to right forewing, but the apex of the wing absent. Right hind wing, length at about 7.5 mm, width 4.6 mm, similar to forewing, but smaller, and overlapping with forewing partially. Left hind wing is similar to left hind wing, but partly folded as preserved. There are many spots on all four wings, symmetric between left and right wings.
Paratypes: CNU-MEC-NN2009319 (Fig. 5E), a partially preserved specimen with forewings and one hind wing, but body absent; forewing, length 9.0 mm, width 5.4 mm, RP forking distal to MA forking; MP 2+3 forking at about the same level of  (Fig. 5F), a specimen with one complete and clear forewing, length 7.4 mm, width 5.2 mm, RP forking distal to MA forking; MP 2+3 forking at about the same level of the forking of MA; the stem of MP 3 about three times as long as the stem of MP 2+3 . CNU-MEC-NN2011069 (Figs 6A, B), a partially preserved specimen, with complete left wings and most of body except for the terminalia, but incomplete right wings in dorsal view. Wings: right forewing, length 11.2 mm, width 7.5 mm, broadly oval, field between C and RA wide; RP forking distal to MA forking; MP 2+3 forking distal to the forking of MA; the stem of MP 3 about twice as long as the stem of MP 2+3 ; CuP, 1A, 2A, single. Right hind wing is similar to forewing, but slightly smaller. Left wings partially preserved. CNU-MEC-NN2011078 (Figs 6C,  D), an almost preserved specimen in dorsal view, with outspread clear wings, but parts of body absent. Wings: Left forewing, length 10.7 mm, width 6.4 mm, RP forking at the same level of the forking of MA; MP 2+3 forking basal to the forking of MA; the stem of MP 3 about four times as long as the stem of MP 2+3 ; with one crossvein between MP 3 and MP 4 , and between 1A and 2A; CuP, 1A, 2A single. Right forewing, similar to left forewing, but individual asymmetry is shown by right wing having MP 3 with two branches, not the typical one branch in the left wing. Hind wings, length 8.2 mm, width 6.2 mm, similar to forewings but smaller, and partially preserved. CNU-MEC-NN2011077 (Fig. 6E), a partially preserved specimen with complete hind wings but parts of forewings and body; Forewing, length at about 10.3 mm, RP forking at the same level of the forking of MA; MP 2+3 forking basal to the forking of MA; the stem of MP 3 about three times as long as the stem of MP 2+3 ; Hind wing, length at about 7.9 mm, width 5.0 mm.
Material Etymology. The specific name is dedicated to Ms. Janet Angeline for her professionalism, dedication and accomplishments in her field and providing inspiration and support to CKS's palaeontology studies.
Remarks. These six specimens exhibit differences in the characters of "RP forking vs. MA forking", "MP 2+3 forking vs. MA forking" and "Length ratio of the stem of MP 3 and the stem of MP 2+3 " , which are considered as intraspecific variations. Willmann (1989) synonymized Choristopsychidae with Agetoparnopidae Carpenter, 1930 because of forewing venation. Novokshonov (2002) synonymized Choristopsychidae and Agetoparnopidae with Permochoristidae Tillyard, 1917 also because of wing venation of the forewing. Based on our new findings about the characters of Choristopsychidae and the reported family of Agetoparnopidae by Carpenter (1930) and Permochoristidae by Tillyard (1917), there are significant differences between Choristopsychidae, Agetopanorpidae and Permochoristidae. For example, the former has broad oval wings (vs. long and narrow), MA vein with 2 branches (vs. 3 branches), MP vein with 5 branches (vs. 6 branches), CuA strongly bent at its mid point (vs. CuA without bending) etc. Therefore, we consider that it is justifiable for Martynov in setting up the family of Choristopsychidae.

Discussion
Based on studies of our specimens and the reported species of Choristopsychidae, we found the wing venation of this family is comparatively stable, that is, the numbers of branches of ScP, RP, MA, MP have almost no changes in these specimens. However we observed significant differences regarding the relative positions between bifurcation points of two different veins, especially the origination locations of the main veins. In the literature of Mecoptera taxonomy, these characters have been used as diagnostic characters for genera or species, such as in Orthophlebiidae, Aneuretopsychidae and so on (Hong and Zhang 2007, Qiao et al. 2012a. Therefore, we contend the character of "the separation of RP+MA from RA distal, basal or at the same level to the separation of MP from CuA" is the generic diagnostic character for Choristopsychidae; and the character of "the relative positions (basal or distal) between the forking of RP+MA and the forking of MP" is the specific diagnostic character. On the other hand, to avoid over classification of species, we also consider the characters of "RP forking vs. MA forking", "MP 2+3 forking vs. MA forking" and "Length ratio of the stem of MP 3 and the stem of MP 2+3 " are intraspecific variations.
Choristopsychids have relatively broad wings, either oval or subtriangular-shaped, with length/width ratio from 1.5 to 2.0, in contrast to long and narrow wings of most mecopterans. To compare relative forewing broadness for representative mecopterans, we summarize the data of forewing length, width and ratio of wing length/width in Table 1 and plot the ratio of wing length/width vs. wing length (in mm) in Fig. 7. The data and Fig. 7 indicate the family of Choristopsychidae has the lowest ratio, meaning broadest forewings among mecopterans. In addition, the data and Fig. 7 seem to show a general trend that for representative specimens of these families, the larger the body size, the narrower the forewings (comparatively higher ratio). The linear regression trend line is represented by Y1 = 0.036*X + 2.620. For example, the family of Cimbrophlebiidae have large body size, with forewing length from 25 mm to 30 mm, and high ratio, with L/W ratio from 3.5 to 4.4 (Bruce 2009, Yang et al. 2012b. It is also noted that Panorpidae have unusually high ratio (more slender), with L/W ratio from 4 to 5, for their relatively small body size, with forewing length from 10 mm to 14 mm (Fu andHua 2009, Zhou et al. 1993). If we exclude the data of Panorpidae, the linear regression trend line is Y2 = 0.056*X + 1.977. The higher value of slope indicates clearer trend that the larger the body size, the narrower the forewings for all these families of Mecoptera excluding Panorpidae.
The oval-shape forewings for choristopsychids are rather unique for mecopterans. Broad subtriangular (Choristopsyche asticta sp. n.) forewings can be found in Pseudopolycentopus (e.g. P. janeannae Ren, Shih & Labandeira, 2010, P. novokshonovi Ren, Shih & Labandeira, 2010, and Sinopolycentropus rasnitsyni Shih, Yang, Ren & Labandeira, 2011 with length/width ratio 2.1, 2.2 and 2.5 respectively (Ren et al. 2010c, slightly narrower than that of C. asticta sp. n. with a subtriangular forewing and a ratio of 2.0. Spots and bands of dark and light color are rather common for many mecopteran fossils from the Middle Jurassic of northeastern China. However, the patterns and many dark and light spots on all four wings, symmetric between left and right wings, are unique for choristopsychids (except for C. asticta sp. n. without dots). It is likely that these spots and patterns on forewings might have served potential functions of mimicry, disruptive camouflage, or mate identification. The symmetric pattern between the left and right wings suggests that these dots may have been genetically controlled for an individual. We do not use the spots and bands as a diagnostic character.
The paratype of Paristopsyche angelineae sp. n. (CNU-MEC-NN2011078) exhibits individual asymmetry by having vein MP 3 with two branches on the right wing, not the typical one branch on the left wing. Numerous cases of asymmetric variations within individual fossil insects have been reported from the Mesozoic of northeastern China. In the paratype of Synapocossus sciacchitanoae Wang, Shih &  Ren, 2012 from Daohugou, China, the left and right forewings of CNU-HEM-NN2007008p/c show some individual variation, i.e., 1 mm of coalescence within the left wing and only a point contact on the right wing (Wang et al. 2012). An odonatan species, belonging to Campterophlebiidae Handlirsch, 1920, has veins MA and MP fusing before the nodus in the left wing whereas the right wing has normal venation (Zhang et al. 2008, Fig. 6). For Plecoptera, the variability of wing venation and the difference between the left and right wings of the same individual have been described in Sinosharaperla zhaoi Liu, Sinitshenkova & Ren, 2007(Liu et al. 2007. Exilibittacus lii Yang, Ren & Shih, 2012 of Bittacidae (Mecoptera) has interesting asymmetric venational characters that RP+MA and MP of its left hind wing having only three branches and RP1+2 and MP3+MP4+CuA1+2 not forking, even though RP+MA and MP of its left and right forewings with typical four branches as those of most hangingflies (Yang et al. 2012a). Also the bittacid Mongolbitacus daohugoensis Petrulevičius, Huang and Ren, 2007 shows asymmetry in the anal veins of the forewings (Petrulevičius et al. 2007).
These new Chinese Choristopsychids, the first record in China, show many venational differences from the previously reported Choristopsyche tenuinervis Martynov, 1937. In addition, these new fossils with well preserved body structure and wings enhance our understanding of the morphological characters of this family, and provide a basis for future phylogenetic studies. Furthermore, these new species from China reveal that the early diversification of Choristopsychidae was well underway by the Middle Jurassic, while broadening the diversity of Mesozoic Mecoptera in China.