One new species of the genus Ischnothyreus Simon, 1893 and re-description of I. yueluensis Yin & Wang, 1984 from China (Araneae, Oonopidae)

Abstract Background The genus Ischnothyreus Simon, 1893 is one of the most speciose genera of Oonopidae, with 114 extant species mainly distributed in the Old World. Currently, 16 species have been recorded in China. New information Two species of the genus Ischnothyreus Simon, 1893 from China are recognised, including one new species, I. yunlong Tong & Li, sp. n. (male, female) from Yunnan. Ischnothyreus yueluensis Yin & Wang, 1984 is re-studied. Descriptions, diagnoses and photos of the two species are provided.


Introduction
Ischnothyreus Simon, 1893 is one of the most speciose genera of Oonopidae, with 114 extant species mainly distributed in the Old World (WSC 2021). This genus is currently placed in the subfamily Oonopinae as they have the characteristic tarsal organ pattern found in this group (Platnick et al. 2012). Members of this genus can easily be recognised by the strong spines present on the femora, tibiae and metatarsi of the first and second legs in both sexes, the distinctive, small, darkened male palps and the distinct, darkly sclerotised, convoluted duct and uniquely-shaped atrium in females (Kranz-Baltensperger 2011, Edward andHarvey 2014).

Materials and methods
Specimens in this study were mainly collected by sieving from forest leaf-litter. The specimens were first examined in 95% ethanol using a Leica M205C stereomicroscope. Details were then studied with an Olympus BX51 compound microscope. Photos were taken with a Canon EOS 750D zoom digital camera (18 megapixels), mounted on an Olympus BX51 compound microscope and Helicon Focus image stacking software (7.6.1 Lite) was used to compile the images. Vulvae were cleared in lactic acid, then immersed in Kaiser's glycerol gelatine for photographs. Scanning electron microscope images (SEM) were taken under high vacuum with a Hitachi TM3030 after critical point drying and goldpalladium coating. All measurements were taken using an Olympus BX51 compound microscope and are given in millimetres in the text.
The specimens are preserved in Shenyang Normal University (SYNU) in Shenyang, China and Hunan Normal University (HNNU), Changsha, China.

Diagnosis
The new species is similar to Ischnothyreus bauri Richard, 2016 (female unknown) in the large retrolateral lobe of the palpal bulb, but can be distinguished by the absence of the ventral protuberance ( Fig. 2G and H

Etymology
The specific name is a noun in apposition from the type locality.

Distribution
Known only from the type locality (Fig. 7).   Fig. 4B and F): six, well developed, ALE largest, PLE smallest, posterior eye row straight from above, procurved from front. Sternum (Fig. 4D): pale orange, longer than wide. Mouthparts ( Fig. 4D and G-I; Fig. 5L): chelicerae, endites and labium orange; chelicerae straight, base of fangs with small stick-shaped sclerotised process, fang groove with field of small denticles; anteromedian tip of endites with one strong, toothlike projection. Abdomen: 0.75 long, 0.46 wide; dorsal scutum well sclerotised, pale orange, covering 4/5 of abdomen width and approximately 5/6 of abdomen length, unfused to epigastric scutum; epigastric and postgastric scutum well sclerotized, pale orange, fused, postgastric scutum covering about 2/3 of abdomen length. Legs: pale orange, femur I with 2 prolateral spines, tibia I with 4 pairs, metatarsus I with 2 pairs of long ventral spines. Leg II spination similar to leg I, except femur with only 1 prolateral spine. Legs III and IV spineless. Sperm pore large, oval, situated at level of anterior spiracles. Palp (Fig. 5A-K): trochanter with ventral projection; femur normal size; patella about as long as femur, not enlarged; tibia with three trichobothria; cymbium fused with bulb; bulb with 2 ventral protuberances, one large and another very small, distal end elongated, with a prolateral lobe and several leaf-shaped membranes, retrolateral lobe small.

Diagnosis
This species is similar to Ischnothyreus concavus Richard, 2016 in the stick-shaped sclerotized process on the male fang base, but can be distinguished by the prolateral lobe (Fig. 5I) of palpal bulb, which is lacking in Ischnothyreus concavus (Richard et al. 2016: fig. 33) and the epigastric area (unmodified (Fig. 6H) vs. with central goggleshaped process (Richard et al. 2016: figs. 36B, C and D)).