On the genus Flexicrurum Tong & Li, 2007 (Araneae, Psilodercidae) from Hainan Island, China

Abstract Three new species of the genus Flexicrurum Tong & Li, 2007, from Hainan Island, China are described: F.wuzhishanensesp. nov. (♂♀), F.yangjiaosp. nov. (♂♀), and F.qishisp. nov. (♂♀). A key to males of species of Flexicrurum is provided. Additionally, the female of F.minutum Tong & Li, 2007, is described for the first time. To date, the genus is endemic to Hainan Island, China. Types are deposited in the Institute of Zoology, Chinese Academy of Sciences (IZCAS) in Beijing.

Prior to this study, only three species from the genus Flexicrurum Tong & Li, 2007, have been described (Tong and Li 2007): F. flexicrurum, F. longispina, and F. minutum. These species are confined to Hainan Island, China, and have been the only representatives of the genus (World Spider Catalog 2019).
While studying new material collected in Hainan Island, we recognized the matched pairs of three new species of Flexicrurum, and a hitherto unknown female of F. minutum, one of the three species described by Tong and Li (2007). This paper describes all of these new discoveries by providing images of their genital organs and close-up photos of their chelicerae.

Materials and methods
Types are deposited in the Institute of Zoology, Chinese Academy of Sciences (IZCAS) in Beijing. All specimens collected were observed and preserved in 95% ethanol. The specimens were measured and examined under a Leica M205 C stereomicroscope, and further morphological details were observed with an Olympus BX41 compound microscope. The left male palp was detached for closer examination. Carapace measurements include the clypeus. The internal genitalia and male bulb were dissected and immersed in lactic acid. An Olympus C7070 wide zoom digital camera (7.1 megapixels) mounted on an Olympus SZX12 stereomicroscope was used to take photos. Photos were stacked with Helicon Focus 6.7.1 to generate images with extended depth of field. The images were post-processed with Adobe Photoshop. Leg measurements are shown as total length (femur, patella, tibia, metatarsus, and tarsus). Leg segments were measured from the retrolateral side. All measurements are given in millimetres (mm). Terminology follows that of Li et al. (2014), Tong and Li (2007) and Deeleman-Reinhold (1995). Coordinates of collecting locations were recorded in Microsoft Excel and imported into ArcGIS 10.2 to generate a map which was subsequently exported to Adobe Photoshop CC 2014 for further editing. The following abbreviations are used in text: ALE anterior lateral eye, ME median eye, PLE posterior lateral eye.  Tong & Li, 2007, resembles Althepus Thorell, 1898, and Leclercera Deeleman-Reinhold, 1995. However, Flexicrurum can be differentiated by the combination of the following characteristics: 1) the tibia of the male palp is strongly rotated inward (vs absence of rotated male palpal tibia in Althepus and Leclercera); 2) presence of a slender bulbal apophysis (vs absence of slender bulbal apophysis in Althepus and Leclercera); 3) cymbium with a strong lateral protrusion (vs cymbium with slightly tilted protrusion in Althepus and Leclercera); 4) cymbium bearing a one-or two-bulge posterolateral cymbial apophysis (vs cymbium with lateral lanceolate or hook-shaped, spine like apophysis in Althepus; cymbium with retrolateral apophysis in Leclercera); 5) absence of promarginal cheliceral teeth (vs 1-2 promarginal cheliceral teeth in Althepus and Leclercera); 6) embolus distinctly short (vs embolus long and slender in Althepus and Leclercera); 7) internal endogyne with the presence of a distinct vertical duct medially bearing different structures of spermathecae (vs absence of the vertical duct in Althepus and Leclercera).

Key to species of Flexicrurum (males only)
1 Cymbium with posterolateral apophysis with a divided tip, i.e., with two bulges or protuberances .. Etymology. The species name is an adjective referring to the type locality; the Chinese pinyin "wǔ zhǐ" means five fingers, and "shān" means mountain. The name is a graphic interpretation of contour of the mountain ranges with a striking resemblance to five fingers.
Distribution. Known only from the type locality (Fig. 9).  Etymology. The species name is a noun in apposition derived from the word for "goat horn" in Chinese pinyin "yángjiǎo". It refers to the shape of the conductor which curves strongly inwards, like a goat horn.
Diagnosis. Flexicrurum yangjiao sp. nov. can be distinguished from F. wuzhishanense sp. nov. and F. qishi sp. nov. by a posterolateral cymbial apophysis with a single tip or bulge (Fig. 4D) (vs a posterolateral cymbial apophysis with two bulges or protuberances (i.e., a divided tip) in F. wuzhishanense sp. nov. and F. qishi sp. nov.), a pointed embolic end (vs hook-liked embolic end in F. wuzhishanense sp. nov. and F. qishi sp. nov.), a shorter laminar apophysis (vs longer in F. wuzhishanense sp. nov. and F. qishi sp. nov.), and the position of the entire bulb is opposite that of the other two species-the laminar apophysis is parallel to the tip of cymbial protrusion (vs laminar apophysis and tip of cymbial protrusion not parallel in F. wuzhishanense sp. nov. and F. qishi sp. nov.).
Distribution. Known only from the type locality (Fig. 9). Etymology. The species name is a noun in apposition derived from the Chinese pinyin "qíshì" (knight) and refers to the ventral view of the bulb which resembles a piece in international chess game representing a knight (Fig. 6A).
Diagnosis. The species is similar to Flexicrurum wuzhishanense sp. nov. Diagnostic features are discussed under F. wuzhishanense sp. nov.
Description. Male (Holotype). Total length 2.45; carapace 1.25 long, 0.75 wide; abdomen 1.20 long, 0.68 wide. Carapace round and brown, with three longitudinal dark brown bands, the middle band is 2 times wider than the lateral bands (Fig. 5C). Fovea shallow and dark brown. Anterior part of thoracic region distinctly elevated. Eye sizes and interdistances: ALE 0.08, ME 0.06, PLE 0.05; ALE-ALE 0.28, ME-ME 0.15, PLE-PLE 0.30, ALE-ME 0.16, PLE-ME 0.18, ALE-PLE 0.13. Chelicerae brown. Cheliceral promargin with lamina of three triangular extensions and no teeth, retromargin with two small teeth (Fig. 8C). Clypeus slanting 0.20 high, medially dark brown and two pale areas laterally. Endites dark brown. Labium slanting and dark brown. Sternum circular with brown complex pattern delimiting a 1/3 medial small pale spot anteriorly and bottom margin. Abdomen elongated, dorsum anterior 2/3 with random dark brown spots, posterior 1/3 with horizontal dark brown striated pattern medially, ventrum anterior half with pair of circular pale areas and ovoid epigastric area, posterior half with random irregular dark brown spots. Legs uniformly brown; measurements: missing (detached from specimens, sequence of legs cannot be differentiated). Palp (Fig. 6A-D): femur slender, swollen at the base, patella swollen and angled ventrally (Figs 5C, 6C), tibia swollen and darker distally, cymbium pale, darker distally, with strong lateral protrusion darker distally, bearing posterolateral cymbial apophysis with two bulges (Fig. 6D); bulb pale brown and pyriform, bearing a pointed laminar apophysis, a slender bulbal apophysis adjacent to embolus which is located further away from conductor; conductor comprising two parts (two slender conductors circling inwards) resembling a broken ring; embolus hook-shaped, curving distally (Fig. 6B).