Taenionemasinensis sp. n., the first endemic species of Taenionema Banks, 1905 (Plecoptera, Taeniopterygidae) from China

Abstract Background The taeniopterygid genus Taenionema Banks, 1905 currently contains 14 species distributed in the Nearctic and the eastern Palearctic Regions. Taenionemajaponicum (Okamoto, 1922) is the only species known from the Eastern Hemisphere, specifically in Japan, Korea, Mongolia, Russia and north-eastern China. The authors recently described the larvae of an undetermined Taenionema species, which was supposed to represent a second Palaearctic species. New information This paper reports the first endemic species of Taenionema Banks, 1905, Taenionemasinensis sp. n. from China, which also represents the second species of Taenionema from the Eastern Hemisphere. Description and illustrations based on male and female adults are provided. The new species is easily distinguished from all congeners by the bilobed abdominal sternum 9 of the male adult. The female adult is characterised by the posteriorly truncate postgenital plate. The male larva is distinguished by the emarginate subgenital plate and hook-shaped paraprocts.


Introduction
The genus Taenionema Banks, 1905 was described as an independent genus, with Taenionema analis Banks, 1905 as the type species (Banks 1905). Taeniopterygidae has been used as a family since Klapálek (1905). Needham and Claassen (1925) later synonymised T. analis with Taenionema pacificum (Banks 1900). Illies (1966) confirmed the familial and generic status of Taeniopterygidae and Taenionema, respectively. Stanger and Baumann (1993) conducted a comprehensive revision of Taenionema focusing on the morphology of adult males and females.
Taenionema currently contains 14 species distributed in the Nearctic and the eastern Palearctic Regions, 13 of which are known from North America (Stanger andBaumann 1993, DeWalt et al. 2023). Taenionema japonicum (Okamoto, 1922) is the only species known from the Eastern Hemisphere, specifically in Japan, Korea, Mongolia, Russia and north-eastern China (Okamoto 1922, Stanger and Baumann 1993, Teslenko 2006, Stewart 2009, Chen 2020. Teslenko (2006) reported the occurrence of T. japonicum in Jilin Province of north-eastern China. Chen (2020) provided new images of T. japonicum adults based on material from Jilin Province.
Chen and Ye (2020) described and provided illustrations of an undetermined Taenionema species based on larvae collected from coastal south-eastern China. The discovery of Taenionema larvae in a low-elevation coastal area is unusual as the genus is typically found in creeks and small rivers at higher elevations (Stanger and Baumann 1993). The morphology of the larvae described in Chen and Ye (2020) was also unique, but the adult morphology remained unknown due to the low population density of adults and the difficulty of rearing larvae indoors. However, the second author of the paper recently revisited the locality documented in Chen and Ye (2020) and collected both adults and larvae of the undescribed Taenionema species. The adult morphology allows for the proposal of a new species based on these specimens.

Materials and methods
The adults were collected by sweep-net and light trap in Zhejiang and Fujian Provinces (Fig. 1). The larvae were obtained by dip-net. All specimens used in this study were preserved in 95% ethanol. Observation of external morphology and measurements were performed with an SDPTOP SZM45 stereomicroscope. Photographs were taken with a Canon EOS 6D digital camera, equipped with a Canon MP-E 65 mm 5X macro lens. All images were optimised and assembled in Adobe Photoshop CS6. Type specimens were deposited in the Insect Collection of Jiangsu University of Science and Technology (ICJUST), Jiangsu Province, China. Terminology follows that of Stanger and Baumann (1993).

Diagnosis
Taenionema sinensis sp. n. can be distinguished from all congeners by the following characters: adult males with deeply notched, bilobed sternum 9; adult females with a posteriorly truncate postgenital plate; male larvae with a notched subgenital plate and hook-shaped paraprocts.

Etymology
The specific epithet refers to the first new species of Taenionema known from China, treated as an adjective.

Biology
Taenionema sinensis sp. n. has been observed to inhabit moderately-sized creeks (to 10 m wide) characterised by fast-flowing, clear water and boulder and cobble substrates ( Fig. 1B and C). Adults of T. sinensis sp. n. were primarily found on streamside plants, with one male adult being captured by a light trap, suggesting a possible positive phototactic response. Adult emergence for T. sinensis sp. nov. occurs in early March. Despite the suitable habitat, the population density of T. sinensis sp. n. is low in both Zhejiang and Fujian Provinces. The habitat was found to be populated with numerous other stoneflies, including species of Leuctridae, Nemouridae, Peltoperlidae, Perlidae, Perlodidae and Styloperlidae.

Discussion
Confirmation of conspecificity between adult females and larvae from Fujian Province and those from Zhejiang Province was based on identical female terminalia and especially the larval morphology. This was further supported by the relatively short distance of approximately 170 km between Mt. Yaowangshan in Zhejiang and Mt. Wuyishan in Fujian. The similarity in the unique larval morphology and geographic proximity provides strong evidence for the conspecificity of these specimens.
The classification of the new species within the genus Taenionema is supported by several distinguishing characteristics, including forked RP and CuA veins in forewings, a medially depressed and laterally elevated hind margin of male sternum 9, distinct lobes on male tergum 10 and eight-segmented cerci (Ricker andRoss 1975, Teslenko andZhiltzova 2009 ). Additionally, the absence of silky cercal fringe hairs in the larvae of T. sinensis sp. n., as described in Chen and Ye (2020), is consistent with other species within the Taenionema genus (Stewart and Stark 2002, Stewart 2009, Teslenko and Zhiltzova 2009). These morphological features provide strong evidence for the placement of the new species within Taenionema.
The newly-discovered species is distinguishable from all of its congeners, including its eastern Palearctic relative, T. japonicum, due to several unique features. These include the deeply notched, bilobed sternum 9 in males, posteriorly truncate postgenital plate in females, as well as emarginate subgenital plate and hook-shaped paraprocts in male larvae (Stanger and Baumann 1993, Chen and Ye 2020). These characteristics make the species remarkable and easily identifiable. Stanger and Baumann (1993) have provided a comprehensive key to males and females of Taenionema, thus there is no need to provide another key to include the remarkable new species.
Taenionema japonicum is a congeneric species that has been previously known to be widespread in the eastern Palearctic Region, including the Jilin Province of north-eastern China (Stanger and Baumann 1993, Chen 2020). However, the discovery of T. sinensis sp. n. in the low-elevation coastal area of south-eastern China has expanded the generic distribution of Taenionema in the Eastern Hemisphere in an unexpected way. With this discovery, it is likely that more reports of the genus will surface in the area between Jilin and Zhejiang Provinces.