A new species and a revised key of the genus Thoradonta (Orthoptera, Tetrigidae)

Abstract A new species of the genus Thoradonta (Orthoptera, Tetrigidae), Thoradonta varispina Zha & Sheng, sp. n., was found in Lengshuihe Nature Preserve, Jinsha, Guizhou, China. It is introduced with a description and photographs and compared with similar taxa. Ecology, habits, and morphological variation of the new species are discussed and illustrated. Generic characteristics of Thoradonta are updated and an updated key to all known species of Thoradonta is given.


Introduction
The genus Thoradonta Hancock belongs to Scelimeninae, Tetrigidae, type species Thoradonta dentata Hancock. To date it includes 21 known species worldwide, distributed in subtropical and tropical Asia (China, Bengal, Hong Kong, India, Indonesia, Malaysia, Myanmar, Nepal, Singapore, Sri Lanka, the Philippines, and Vietnam) and equinoctial Africa (Zha et al. 2016b).
During investigation of species diversity in Lengshuihe Nature Preserve, Jinsha County, Guizhou Province, China during 3-10 Aug 2015, a new species of the genus Thoradonta was found, Thoradonta varispina Zha & Sheng, sp. n. A description and illustrations introduce the species, and it is compared with similar taxa. Ecology, habits, and morphological variation of body structure of the genus Thoradonta are discussed. Generic characteristics of Thoradonta are updated and an updated key to all known species of the genus is given.

Material and methods
Specimens were photographed using a stereomicroscope (Keyence VHX-1000). Morphological terminology and measurement landmarks follow Shishodia (1991) and Zheng (2005). Measurements are given in millimeters (mm). Type specimens are deposited in the Specimen Room of the School of Life Sciences, Huaibei Normal University, Huaibei, Anhui, China.
Description. Female. Body size small, covered with numerous small granules and many nodules.
Head. Head not protruding over level of pronotal surface; vertex 1.8-2.0 times as wide as one eye, anterior margin straight, protruding but not surpassing anterior margins of eyes, lateral margins folded upwards but not surpassing top of eyes; median carina conspicuous and protruding in anterior half which is visible before eyes in profile, while obscure or absent in posterior half; vertex together with frontal ridge arcuate and protruding, distinctly concave between lateral ocelli, then strongly arched and protruding between antennae, longitudinal furrow between antennae slightly wider than diameter of first segment of antenna, margins of longitudinal furrow finely serrate. Antenna filiform, 17-segmented, inserted slightly below lower margins of eyes, length of longest segment (segment IV, male in VIII) 4.5 times its width. Eyes globose,   protruding but not above level of pronotum; lateral ocellus situated slightly below middle of anterior margin of eye.
Thorax. Pronotum very coarse, covered with numerous small granules and many nodules; middle of anterior margin little concave; lateral keels of prozona erected, distal part higher than basal part, slightly contracted backward, sometimes distal part excessively contracted inward. Midkeel not reaching anterior margin of pronotum, otherwise nearly entire, in profile upper margin of pronotum distinctly undulate with wave peaks becoming lower backward. These sinusoidal waves lamellate and erected, first highest, with intumesced base, both sides of intumescence with a pair of big nodules at margins of pronotum; second lamella longest and undulate, on both sides pronotal disc distinctly concave followed by a pair of long oblique nodules, and lateral margins of pronotum distinctly folded upwards; the latter midkeel with 4-5 lamel-lae of intumesced base. Humeral angle obtusely angled; a pair of abbreviated carinae present between shoulders, slightly contracted forwards; pronotum slightly uplifted between shoulders; hind process of pronotum long cone-shaped, reaching (few specimens) or slightly surpassing (most specimens) apex hind femora, distal part slightly down-curved and apex sharp. Posterior angles of lateral lobes of pronotum laminate and expanded and extending outwards, apex varies distinctly in different individuals: upper lobe not produced, slightly produced or triangularly laterally produced; subtruncate behind which is margined with fine teeth (Fig. 3). Posterior margin of each lateral lobe has two concavities. Visible part of tegmina ovate, 2.7 times as long as wide, apex rounded. Hind wing not reaching top of hind process of pronotum, not reaching or reaching apex of hind femur. Margins of all femora with fine teeth; upper margin of fore femur slightly undulate, lower margin distinctly undulate; upper and lower margins of mid femur distinctly undulate; mid femur slightly wider than fore femur and visible part of tegmen, not narrowed or thicker from basal to distal area. Hind femur about 2.5 times as long as wide, rear of upper margin before antegenicular denticle slightly protruding; antegenicular denticle isolated and long triangular, its apex relatively sharp, genicular denticle fingered extending backward and apex obtuse. Hind tibia distally slightly wider than basally, outer side with 5-7 spines, inner side with 4-6 spines; first segment of hind tarsus 1.3-1.4 times longer than third, third pulvillus longer than first and second, apex of third pulvillus relatively obtuse, apices of first and second sharp.
Abdomen. Ovipositor: upper valvulae 3.3 times as long as wide, outer margins of upper and lower valvulae with saw-like teeth. Posterior margin of subgenital plate: narrowing backward; middle triangularly protruding, sometimes this protrusion folded inward, forming a basal concavity and a protrusion on both sides (Fig. 2d, e).
Coloration. Body dark brown. Antenna brown, distal segments darker than basal segments; hind wings black; for and mid femora and tibiae with 3 yellowish brown bands each, bands of all femora obscure; lower outside of hind femur black, center of inner side of hind femur dark brown; hind tibia with 2 long yellowish brown bands.
Male. Body size slightly smaller than female. Antenna 16-segmented. Fore femur nearly the same as that of female; mid femur distinctly wider than fore femur and visible part of tegmen, narrowing from basal to distal side, and basal part thicker than distal part. Subgenital plate short cone-shaped, apex bifurcate but not bidentate.
Ecology and habits. All specimens of the new species were collected in humid, sandy, and stony environments alongside streams (Fig. 4). Body surfaces of most individuals are covered tightly by numerous sand grains. They move frequently in sunshine, and they feed on mosses, algae, lichens and all sorts of humus. Hind process of pronotum shorter, not reaching or reaching apex of hind femur (Fig. 6a, b)  Hind process of pronotum longer, surpassing apex of hind femur (Fig. 6c-e) ...9 6 Hind process reaching apex of hind femur (Fig. 6b); lower lobe of posterior angle of lateral lobe of pronotum acutely produced (Fig. 5c)

7
Wings shorter, not reaching apex of hind process; third pulvillus of first segment of hind tarsus longer than second (Fig. 5b) Upper lobe of posterior angle of lateral lobe of pronotum obliquely dentate (Fig. 5b) Body size stout; hind process of pronotum surpassing slightly beyond apex of hind femur (Fig. 6c)   Spine of upper lobe of posterior angle of lateral lobe of pronotum pointing laterally (Fig. 5a, c)  Vertex wider, 1.5-2.0 times as wide as one eye (Fig. 6d)

Discussion
Species of the genus Thoradonta generally live in humid and sandy places near streams, rivers, or ponds. They move frequently in sunshine, and they generally feed on mosses, algae, lichens and all sorts of humus. Though provided with developed hind wings they seldom really fly, instead their hind femora are well-developed, suitable for jumping when disturbed. Colors of their bodies are generally adapted to the soil of their habitats. Apart from generally coarse an uneven, body surfaces of most individuals were often tightly covered by numerous sand grains. We infer that they lay eggs in sandy soil, and most of their life time they may conceal their body in sandy soil (Zha et al. 2016a) to avoid bad environments such as low temperature, being preyed, rain, drought etc.; when temperature is high and light is good, they may crawl out from sandy soil for feeding and mating. Their small size and long-term living in sandy soil made them easily be preserved during evolution. Additionally, based on collecting times of all known adults (from beginning of April to end of November), we infer part or all species of the genus living outside the tropics may overwinter as adults (the genus from tropical countries do not hibernate at all). According to T. varispina sp. n., and comparing with descriptions of 21 known species of the genus Thoradonta (Hancock 1909, 1915, Günther 1938, Zheng 1983, 1996, 2005, Blackith and Blackith 1987, Shishodia 1991, Zheng and Liang 1991, Podgornaya 1994, Ingrisch 2001, Deng et al. 2006, Zha et al. 2016b, generic characteristics of Thoradonta should be updated as follows. Body size small. Vertex equal to or wider than one eye, frontal ridge distinctly protruding forward between antennae. Antenna filiform, inserted between or below lower anterior margins of eyes. Eyes globular and prominent, lateral ocellus situated in or slightly below middle of anterior margin of eye. Distal segments of maxillary palpus slightly compressed. Pronotal disc generally covered with many nodules; midkeel undulate, partially lamellate and erected before shoulders; pronotum slightly uplifted between shoulders; a pair of abbreviated carinae present between shoulders; lateral margins of pronotum behind humeral angles folded upwards; hind process of pronotum wedge-shaped, not reaching, reaching or surpassing apex of hind femur; posterior angle of lateral lobe of pronotum laminate and expanded and extending outwards, apex varies conspicuously: 1) upper lobe generally produced, spinose or acutely angled, extending laterally or obliquely backward; 2) lower lobe generally truncate, sometimes also produced and obtusely angled or acutely angled; 3) both upper and lower lobes not produced or produced inconspicuously, and apex truncate or subtruncate. Visible part of tegmina ovate, hind wing normal but invisible in T. butlini. First segment of hind tarsus generally longer than third. Podgornaya (1994) indicated two forms of wings and pronotum (brachypterous and macropterous) as occurring in T. spiculoba specimens collected from Vietnam, as well as T. apiculata from Thailand reported by Storozhenko and Dawwrueng (2015) recently, while in T. varispina sp. n., though varying more or less it is indistinct. So we think the view that similar specimens with different lengths of both wings and pronotum in Tetrigidae are two different species is debatable, at least not so in T. varispina sp. n.. Notably for T. varispina sp. n., the apex of the posterior angle of the lateral lobe of pronotum varies conspicuously between individuals, but never forms into a spine, which is easily distinguished from other spinose species of the genus. The morphological variation of apex of lateral lobe of pronotum from spinose to truncate indicates that Scelimeninae is very close to Metrodorinae in phylogeny, and this finding would help studying taxonomy and evolution of these Tetrigidae insects.