New Chinese record of the genus Spinonychiurus (Collembola, Onychiuridae), with the description of a new species

Abstract A new collembolan species is described, Spinonychiurus sinensis sp. n., which has seven chaetae in the distal row of the tibiotarsi. It is placed in the genus Spinonychiurus due to two important characters: the two subsegments on Abd. III sternum and the absence of d0 on the head. This is the first report of the genus Spinonychiurus in China. The diagnosis of Spinonychiurus is broadened and the key to the world species is provided.


Introduction
The genus Spinonychiurus was established by Weiner (1996) for the Scottish species Onychiurus edinensis Bagnall, 1935, and it was assigned to the tribe Onychiurini Börner, 1901 as having compound vesicles on the postantennal organ. Kaprus' and Tsalan (2009) revised the diagnosis characters of the genus and moved the genus into the tribe Thalassaphorurini Pomorski, 1998 by the structure of the furcal area and the distinct S-chaeta on the antennae. So far, only four species of the genus Spinonychiurus are reported throughout the world: S. edinensis, S. epaphius Kaprus' & Tsalan, 2009 from Ukraine, S. subedinensis (Arbea & Jordana, 1985) from Spain and S. vandeli (Cassagnau, 1960) from France.
During our study on specimens collected from Changbai Mountain Range, we found a new species closest to the genus Spinonychiurus Weiner, 1996 but having 7 chaetae in the distal row of tibiotarsi (there are 11 in Spinonychiurus according to Kaprus' and Tsalan (2009)). In the present paper, we assign the new species to the genus Spinonychiurus with two important characters: two subsegments on Abd. III sternum and the absence of d0 on the head. The description of the new species and the broadened diagnosis of the genus are given below. An updated key to the species of the genus Spinonychiurus is provided.

Material and methods
Specimens were mounted in Marc André II solution, after clearing in lactic acid, and were studied using a Nikon Eclipse 80i microscope. Material is deposited in the Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun (NEIGAE).
The pseudocelli and pseudopores formulae are the number of pseudocelli or pseudopores per half-tergum or half-sternum. The S-chaetae formula is the number of Schaetae per half-tergum or half-sternum from head to Abd. VI.
Derivatio nominis. Named for the first recordof the genus Spinonychiurus in China. Ecology. Found in the coniferous forest. Discussion. The new species is closest to the genus Spinonychiurus in two important characters: two subsegments on Abd. III sternum and the absence of d0 on the head. However, it does not fit the current definition of the genus as proposed by Kaprus' and Tsalan (2009) in having 7 chaetae in the distal row of tibiotarsi instead of 11. The distal tibiotarsal chaetae have been verified to be an unstable character in the generic level (Sun et al. 2010;Sun et al. 2011;Sun and Zhang 2012;Sun et al. 2013), so we propose the placement of the new species in the genus Spinonychiurus and broaden its diagnosis accordingly. The main diagnostic characters of all known species of the genus are given in Table 1 and a key to these species is provided below.  -6,5/4-5,8,8-10/9-13,9-12,9-14,9-14,7- Bagnall (1935) and Weiner (1996); ** the ventral pso formula has been verified by Javier Arbea (based on the type materials collected in University of Navarra); *** the number of chaetae in distal row of tibiotarsi in S. edinensis and S. vandeli has been verified by Louis Deharveng (based on the collections in Muséum National d'Histoire Naturelle).  (Cassagnau, 1960)