﻿Cave-inhabiting Cheliferidae (Arachnida, Pseudoscorpiones) from Thailand, with description of four new species of Metachelifer Redikorzev

﻿Abstract Four new species of the genus Metachelifer Redikorzev, 1938 are described from caves in the provinces of Tak (M.takensissp. nov. and M.thailandicussp. nov.), Chiangmai (M.mahnertisp. nov.), and Nakhon Ratchasima (M.chenisp. nov.). An identification key is provided to all known world representatives of the genus Metachelifer.

Males of the genus Metachelifer can be characterized by the carapace surface with tubercles; coxa IV with an anterolateral process and coxal sac; sternite III uplifted laterally and extending to short thorns; leg I tarsus lateral claw shorter than mesal one; subterminal seta simple (Redikorzev 1938;Dashdamirov 2006). While identifying pseudoscorpion specimens collected from Thailand in 2014-2016, four new caveinhabiting species of Metachelifer were found and are described here.

Materials and methods
The specimens were examined with a Leica M205FA stereomicroscope and an Olympus CX31 compound microscope. The specimens are 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. Photographs were taken using a Canon 6D Mark II camera fitted with a Laowa 25 mm f/2.8 2.5-5 × and 100 mm F2.8 2.0 × ultra macro lens. The final high depth of field images were stacked from 30 to 80 single photos using Helicon Focus 7.6.1., and CorelDRAW 2018 and SAI 2 software 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) and Muséum national d'Histoire naturelle (MNHN; Paris, France).
Identification key to the species of Metachelifer Diagnosis. Troglobiont habitus. This new species is distinguished from other members of the genus Metachelifer by the following combination of characters: carapace with 100-101 setae; coxal sac occupying 1/2 of coxal length; male anterior genital operculum without tubular setae; female anterior genital operculum with 31 setae (24 of them tubular) and two lyrifissures; posterior operculum with 12 setae, without lyrifissures.
Etymology. Latinized adjective, derived from the last name of the collector, Zhi-Gang Chen.
Distribution. Thailand (Tak). Diagnosis. Troglobiont habitus. This new species is distinguished from other members of the genus Metachelifer by the following combination of characters: anterior margin of carapace with 6 denticuloclavate setae and a total of 86-88 setae; chelicera galea with 2 short branches; male movable chelal finger 0.96-0.98 × and female 0.93-0.95 × longer than hand with pedicel length; male anterior genital operculum without tubular setae; female genital posterior operculum with 6 setae, without lyrifissures.
Etymology. Latinized adjective, derived from the country of Thailand, where the type locality is located.