Revised concept of the fossil genus Oviparosiphum Shaposhnikov, 1979 with the description of a new genus (Hemiptera, Sternorrhyncha, Aphidomorpha)

Abstract This paper presents a revision of the aphid genus Oviparosiphum, which is known from the Cretaceous period. Redescriptions of two species: Oviparosiphum jakovlevi Shaposhnikov, 1979 and Oviparosiphum baissense Shaposhnikov & Wegierek, 1989 are made, and an updated diagnosis of this genus is provided. Oviparosiphum baissense is the type species of a newly described genus Archeoviparosiphum gen. n. Five other species of Oviparosiphum are also transferred to the new genus. The basis for their separation from Oviparosiphum is the structure of the siphunculi and ovipositor. A key is provided to the genera of Oviparosiphidae.


Introduction
One aphid family known only from fossils is Oviparosiphidae. Representatives of this family are known from several localities (China, Germany, Mongolia, Russia) but originated within a relatively short time span, from the Early/Middle Jurassic to the end of the Early Cretaceous. The oldest genus is Grimmenaphis Ansorge, 1996, described from the Lower Jurassic deposit of Grimmen (Germany). However, it is known only from an isolated wing (Ansorge 1996). The oldest undoubted representative is Khotontaphis Shaposhnikov & Wegierek, 1989 from the Upper Jurassic/Lower Cretaceous Khotont deposit (Mongolia). More Oviparosiphidae are known from the Early Cretaceous: Acanthotrichaphis Shaposhnikov & Wegierek, 1989, Dinaphis Shaposhnikov & Wegierek, 1989, Expansaphis Hong & Wang, 1990, Oviparosiphum, Sinoviparosiphum Ren, 1995and Vitimaphis Shaposhnikov & Wegierek, 1989, but they are absent from Upper Cretaceous sediments (Heie and Wegierek 2011).
This family is highly diverse morphologically, but the simultaneous occurrence of the ovipositor and siphunculi constitutes its most characteristic feature (Shaposhnikov 1979). The first described aphid with both these structures visible was Oviparosiphum jakovlevi from the Lower Cretaceous Bon-Tsagan deposit (Mongolia), which is the type species of the genus Oviparosiphum (Shaposhnikov 1979). To date, the genus includes seven species. The present paper revises the species originally placed in Oviparosiphum. It also emends its diagnosis and describes a new genus.

Material and methods
The material consisted of 44 aphid fossil specimens borrowed from the collection of the Institute of Palaeontology, Russian Academy of Sciences in Moscow. The fossils were preserved in the form of two imprints -"obverse" and "reverse", marked as ±. The material was analyzed using standard palaeoentomological research methods (Rasnitsyn 2002). Specimens were photographed using a Nikon SMZ1500 stereoscopic microscope and a Nikon Eclipse E600 polarized light microscope. Selected body parts were photographed using Philips XL 30 TMP ESEM and Tescan Vega scanning electron microscopes (with the backscattered electron detector (BSE) in the low-vacuum mode) for better analysis of their morphology. Photographs and measurements were made in the NIS-Elements program. The figures are based on the combined drawings of reverse and obverse imprints, while the photographs represent only one imprint. All measurements are given in mm.
The imprints were collected from two localities: Baissa, Russia and Bon-Tsagaan, Mongolia. Both of them are Lower Cretaceous deposits.

Geological settings
Baissa is one of the richest deposits and most important localities of fossil insects from the Early Cretaceous. More than 10 000 specimens of insects have been collected from there (Rasnitsyn and Zherikhin 2002). It is located in the Asian part of Russia, in Transbaikalia, in the Buryat Republic, on the left bank of the Vitim River (Kania and Wegierek 2008). The Baissa deposit belongs to the Zaza Formation of approximately Berriasian age (Rasnitsyn et al. 1998). This lithostratigraphic unit is characteristic of the Lower Cretaceous sediments throughout western Transbaikalia. It is built mainly of sandstone, limestone, marl and bituminous shale (Zherikhin et al. 1999).
Bon-Tsagan (= Bon-Tsagaan) is one of the richest Mesozoic insect remains deposits in Mongolia, and one of the best known and richest in the world. Numerous outcrops of mudstone and marls are widely distributed in Central Mongolia, south of the recent Lake Bon-Tsagaan-Nur (Rasnitsyn and Zherikhin 2002). The exact age of the lacustrine sediments of Bon-Tsagaan is estimated at the Early Cretaceous, probably the Aptian. Fossils are well preserved in lacustrine sediments of the lake, which was situated in a mountain valley (Ponomarenko 2013).

Systematic palaeontology
Key to the genera of the family Oviparosiphidae:  4A), connected in the middle of the epicranium with lateral sutures. On head, narrow oblique slats running from front and lateral edges to the posterior part of the head. Diameter of ocelli 0.05; distance between ocelli 0.24. Segment I of antennae (0.05) shorter than segment II (0.08) (Fig. 4B). Secondary rhinaria arranged in transverse rows ( Fig. 2A) (1.67) slightly curved, leaving proximal part of pterostigma at an angle of 25° and running close to it. Pterostigma pointed, short and wide; 3 times longer (0.93) than wide (0.31). Hind wing with two cubital vein. Apical part of abdomen slightly sclerotized (Figs 2C,4C). Basal diameter of siphunculus 0.13 (Fig. 4D). Diameter of siphunculus aperture 0.10. Ovipositor with valvae I and III well preserved (Fig. 4E). Tergite IX of abdomen clearly visible. Subgenital plate wider than base of ovipositor, 5 times wider than long. In the middle part, its anterior edge forms an indentation reaching half of the length of the plate.
Diagnosis. Seven antennal segments. Secondary rhinaria slightly ellipsoidal, smaller than secondary rhinaria of Oviparosiphum. Vein CuA 1 connected with the main vein Sc + R + M. Pterostigma short, at most 5 times longer than wide. Abdomen without setae. Siphunculi in form of pores. Ovipositor small and rudimentary. Etymology. The name is a combination of the Greek word archaios (meaning 'ancient') and the genus Oviparosiphum.

Discussion
The first species of the genus Oviparosiphum, O. jakovlevi was described in 1979 by Shaposhnikov and assigned to a new family Oviparosiphidae. The diagnostic features were the following: antennae with annular secondary rhinaria, siphunculi in the form of truncated cones with a height less than the diameter of the wide aperture, and a large conical ovipositor, most likely composed of four valvae (Shaposhnikov 1979). New techniques made a detailed study possible, confirming the presence of these features and allowing to redescribe the type species of the genus Oviparosiphum. Additionally, analysis of the antennal morphology showed that the secondary rhinaria of Oviparosiphum jakovlevi are slightly ellipsoidal and occur in dense, transverse rows. The second species assigned to this genus was O. baissense from the Baissa deposit (Lower Cretaceous, Russia), described on the basis of a single imprint (Shaposhnikov and Wegierek 1989). The large number of specimens available for the present study permitted a very accurate redescription of the species. The presence of pore-shaped siphunculi has been clearly demonstrated, in contrast to the original description, which highlighted the short cone-shaped siphunculi. The characteristics that distinguish these two species of the genus Oviparosiphum from other genera in the family are similar length of both cubital veins and vein Rs leaving proximal part of the pterostigma. These features remain valid but more attention is paid to the abdomen structure. Only one other genus -Khotonaphis -has clearly truncate conical siphunculi, but its ovipositor is not as well developed as in Oviparosiphum jakovlevi (Shaposhnikov and Wegierek 1989). The species Oviparosiphum latum, described from the Early Cretaceous of China, is more problematic because vein Rs leaves the distal part of the pterostigma, and the fact that the exact structure of the secondary rhinaria is unknown (Hong and Wang 1990). However, the drawings suggest that the siphunculi are pore-shaped, which enables it to be reclassified as a member of the new genus.
In the original description of Paroviparosiphum syn. n. and Mesoviparosiphum syn. n. the authors indicated 5-segmented antennae, annular secondary rhinaria and poreshaped siphunculi as being diagnostic features of both genera (Zhang et al. 1989). However, on the basis of drawings, it could be stated that the antennae are 7-segmented, typical of the Oviparosiphidae, and that the secondary rhinaria are most likely ellipsoidal. Nevertheless the siphunculi seem to be pore-shaped, which makes it possible to include these genera also in Archeoviparosiphum.

Conclusion
Previously the genus Oviparosiphum consisted of seven species. It is now limited to a single species, O. jakovlevi, with clearly truncate conical siphunculi and a well-developed ovipositor. The other species have been transferred to a new genus Archeoviparosiphum gen. n.; all these species have pore-shaped siphunculi and a rudimentary ovipositor.