﻿Five new troglobitic species of Tyrannochthonius (Arachnida, Pseudoscorpiones, Chthoniidae) from the Yunnan, Guizhou and Sichuan Provinces, China

﻿Abstract Five new species of the genus Tyrannochthonius Chamberlin, 1929 are described from caves in the provinces of Yunnan (T.huilongshanensissp. nov., T.xinzhaiensissp. nov., and T.yamuhensissp. nov.), Guizhou (T.dongjiensissp. nov.), and Sichuan (T.huaerensissp. nov.). An identification key is provided for all known representatives of the genus Tyrannochthonius from China.

The pseudoscorpion genus Tyrannochthonius was erected by Chamberlin for the Thai type species Chthonius terribilis With, 1906 (by original designation) (Chamberlin 1929). The genus Tyrannochthonius is characterized by tergites V-IX each with eight setae at most; long coxal spines; apodeme of movable finger normal, not complex or strongly sclerotized; the sub-basal trichobothrium is positioned midway between sub-terminal and basal, or nearer to sub-terminal; chelal fingers usually straight in dorsal view; the hand of chela normal, not narrowed at base of fingers; chelal hand usually with a single large, medial acuminate spine-like seta near the base of the fixed finger, but this can be reduced or absent (Muchmore and Chamberlin 1995;Edward and Harvey 2008). During the identification of pseudoscorpion specimens collected from the Yunnan-Guizhou Plateau from 2017 to 2019, five new cave-inhabiting species of Tyrannochthonius were found, which are described in this article.

Materials and methods
The specimens were preserved in 75% ethanol. They were cleared in lactic acid for 12-24 h at room temperature and, after the study, washed in distilled water and returned to alcohol. The specimens were examined with a Leica M205FA stereomicroscope and an Olympus CX31 compound microscope. Photographs were taken using a Canon 6D Mark II camera fitted with Laowa 25 mm f/2.8 2.5-5X and 100 mm F2.8 2.0X Ultra Macro lenses. The final high depth-of-field (DoF) images were stacked from 30 to 80 single photos using Helicon Focus 7.6.1., and CorelDRAW 2018 and SAI 2 softwares were used to draw the figures. The type specimens of the new species are deposited in the collection of the Museum of China West Normal University (MCWNU; Sichuan, China).
Dimensions (mm, length/width or, in the case of the legs, chela, and chelal hand, length/depth).
Etymology. Latinized adjective, derived from the village of Huilongshan, which is near the type locality.
Dimensions (mm, length/width or, in the case of the legs, chela, and chelal hand, length/depth).
Males (  Diagnosis (male, female unknown). Troglobiont habitus. This new species is distinguished from other members of the genus Tyrannochthonius by the following combination of characters: carapace without eyes or eyespots, anterior margin with four setae; epistome present; tergites II-VI with four setae; coxae II with ten terminally indented coxal spines on each side; apex of coxa I with long and rounded anteromedial process, near the apex with a seta; chelal hand dorsal surface with chemosensory setae. Fixed chelal finger with 25 teeth and 20 intercalary teeth, movable chelal finger with 22-24 teeth and three or four intercalary teeth. Pedipalpal femur 6.06-6.07× longer than broad, length 0.97-0.99 mm; chela 7.63-7.66× longer than deep, length 1.45-1.46 mm; ratio movable chelal finger/chelal hand 1.91-1.92×.
Etymology. Latinized adjective, derived from the river of Yamuhe, which is near the type locality.
Dimensions (mm, length/width or, in the case of the legs, chela, and chelal hand, length/depth).  Key to the species of Tyrannochthonius known from China (subspecies not included) similar to that of T. zhai, but the new species have a carapace with 18 setae and tergites I-IV each with two setae; the latter carapace only with 16 setae, and tergites I-IV each with four setae. There are only 16 setae on the carapace of T. chixingi, the other species have 17 or 18 setae. T. huaerensis sp. nov., T. huilongshanensis sp. nov., T. xinzhaiensis sp. nov., and T. yamuhensis sp. nov. are different from the remaining species (except T. antridraconis) in that the new species have tergites I-II each with three or four setae, while the latter only has two setae. In the new species, the chelal hand presents chemosensory setae on the dorsum, while in T. antridraconis they are absent. T. huilongshanensis sp. nov. and T. yamuhensis sp. nov. have intercalary teeth, the former with ten coxal spines and chela 7.63-7.66× longer than broad; in the latter, with eight coxal spines and chela 5.61-5.66× longer than broad. In T. huaerensis sp. nov., the anterior margin of the carapace with four setae, a slender and pointed epistome, palpal femur 8.92-8.95× as long as broad, and movable finger retrolateral margins weakly curved between st and sb trichobothria; in contrast, in T. xinzhaiensis sp. nov. the anterior margin of the carapace with five or six setae, epistome very small, palpal femur 6.94-6.97× as long as broad, movable finger retrolateral margins straight between st and sb trichobothria. In the known species, the chemosensory setae on the dorsal surface of the chelal hand are absent, while in the new species, there is a row of five to seven setae on the dorsal surface of the chelal hand.