Study on Tullbergiidae of Tibet, China I. Metaphorura, Mesaphorura and Prabhergia (Hexapoda, Collembola)

Abstract The Tullbergiidae of Tibet is studied for the first time and the genus Metaphorura Bagnall, 1936 is firstly recorded in China. Metaphorura motuoensis sp. n. from southeastern Tibet is described and illustrated. It is characterized by the presence of 1+1 pseudocelli on thoracic segment I, few vesicles (14 -16) on PAO, pseudocellar formula as 11/111/11111, all pseudocelli of type II, setae p4 on abdominal segment V as microsetae, weakly differentiated sensory seta p3 on abdominal segment V, absence of median process on Abd VI. In addition, Mesaphorura yosii (Rusek, 1967), Mesaphorura hylophila Rusek, 1982, and Prabhergia imadatei Tamura & Zhao, 1996 are recorded in Tibet for the first time. The type specimens of P. imadatei are re-examined and errors in the original description of chaetotaxy are corrected.


Introduction
The knowledge of the taxonomy of Tullbergiidae from China is quite insufficient and only five species have been recorded to date (Rusek 1967;Tamura and Zhao 1996;Gao 2007;Bu et al. 2013;Bu and Gao 2015).There are no records of Tullbergiidae from Tibet. During an investigation of soil arthropods in southeast Tibet in November 2015, nearly 200 specimens belonging to the family Tullbergiidae were obtained. They were identified as four species including one new species of the genus Metaphorura Bagnall, 1936. The new species is illustrated and described in the present paper.

Materials and methods
Specimens were collected by Berlese-Tullgren funnels and preserved in 80% ethanol. The material was mounted on slides in Hoyer's solution and dried in an oven at 60 °C for identification. Observations were done with a phase contrast microscope. Photos were taken by a digital camera installed on the microscope. The type specimens are deposited in Shanghai Natural History Museum (SNHM), Shanghai, China. In the description we use the nomenclature for morphological features following Dunger and Schlitt (2011). Pseudocellar types after Weiner and Najt (1991). Antennal chaetae notation is made following the notation of Rusek (1971). Formula of tibiotarsal chaetotaxy follows Fjellberg (1991).
Abbreviations used in the descriptions: Th. thoracic segment, Abd. abdominal segment, Ant.

Taxonomy
Genus Metaphorura Bagnall, 1936 Diagnosis. Habitus more or less slender. Granulation of the integument moderately fine, with stronger granulation only on head and areas of Abd VI. Usually no crescentic ridges. A median process usually present ventrally between Asp. Antennal segment III with two large sensory clubs, bent towards one another, two small sensory rods and three protecting papillae. Postantennal organ with 14-28 vesicles in two rows. Pseudocelli clearly delimited, with two rows of parallel stripes in the centre (type II). Asp strong, distinctly longer than the claw of leg III.

Distribution.
The genus Metaphorura includes nine species found in Holarctic regions (Dunger and Schlitt 2011;Bellinger et al. 1996Bellinger et al. -2017. It is newly recorded from China in this paper. Diagnosis. Metaphorura motuoensis sp. n. is characterized by the presence of pseudocelli on thoracic segment I, few simple vesicles (14-16) on PAO, pseudocellar formula as 11/111/11111, all pseudocelli of type II, p4 on abdominal segment V as microsetae, less differentiated sensory setae p3 on abdominal segment V, absence of median process on Abd VI. Bisexual.
Etymology. The species is named after the Motuo county where the type specimens were collected.
Distribution. Known only from the type locality.
Remarks. There are two genera of Tullbergiidae with two anal spines, three protecting papillae, three thick sensory clubs on antennal segment III, and an elongate PAO and body longer than 0.7 mm: Delamarephorura and Metaphorura. The new species better fits Delamarephorura in the presence of crescent ridges on Abd. VI, which are absent in Metaphorura, and the presence of a "median process" on Abd. VI which is present in Metaphorura (present or absent in Delamarephorura). However, according to Janion et al (2013): "the discrimination between Delamarephorura and Metaphorura needs to be reevaluated" for uncertainties about the state of some diagnostic characters. The new species is therefore provisionally assigned to the genus Metaphorura, awaiting the validation of Delamarephorura. Biogeographically, Tibet is part of the Holarctic region where the genus Metaphorura is distributed, while Delamarephorura is only known in Africa and in Vietnam. Metaphorura motuoensis sp. n. has few simple vesicles (14-16) on PAO and lacks the median process on Abd. VI which clearly separate it from other congeners. It is similar to M. affinis (Börner, 1902) in the presence of simple vesicles on PAO and the pseudocellar formula on the body, but differs in the presence of a crescentic ridge on Abd. VI, fewer vesicles on PAO (20-25 vesicles in M. affinis), two pairs of m-setae m3 and m4 on Abd IV (three pairs of m-setae in M. affinis: m2, m3, m4), and absence of median process on Abd. VI (presence of a pointed projection in M. affinis) and less differentiated sensory seta p3 on abdominal segment V (flame-like p3 in M. affinis). It is even more similar to Delamarephorura capensis Janion, Deharveng & Weiner, 2013, from which it differs by seta p1 on head much longer than p2 (versus of same size in D. capensis). ( Distribution. Widely distributed in Palaearctic region. In China the species was recorded in Hebei (Bu and Gao 2017) and for the first time in Tibet in this paper. Tamura  Distribution. The species was only known from its type locality in Yunnan Province, southeast China. It is here recorded for the first time in Tibet.

Prabhergia imadatei
Remarks. The description of dorsal chaetotaxy of Prabhergia imadatei in the original paper contains some errors, such as nominations and numbers of anterior and medial setae on Th. II and III, Abd. I-V. The type specimens were examined and a revised dorsal chaetotaxy of the species is given below in Table 2. Table 2. Dorsal Chaetotaxy of Prabhergia imadatei (revised).