Redefinition of the genus Allonychiurus Yoshii, 1995 (Collembola, Onychiuridae) with description of a new species from China

Abstract In this paper, we describe a new species of the genus Allonychiurus Yoshii, 1995, characterized by the presence of an apical swelling on the fourth antennal segment as well as a combination of chaetotaxic and pseudocellar characters. The genus Allonychiurus is redefined. Four of its species are considered as incertae sedis: Allonychiurus michelbacheri (Bagnall, 1948), Allonychiurus spinosus (Bagnall, 1949), Allonychiurus caprariae (Dallai, 1969) and Allonychiurus sensitivus (Handschin, 1928). The three species Allonychiurus borensis (Beruete, Arbea & Jordana, 1994), Allonychiurus sensilatus (Thibaud & Massoud, 1979) and Allonychiurus vandeli (Cassagnau, 1960) are removed from Allonychiurus and placed in Micronychiurus Bagnall, 1949, Thalassaphorura Bagnall, 1949 and Spinonychiurus Weiner, 1996 respectively. The synonymy of Thibaudichiurus Weiner, 1996 with Allonychiurus is rejected and Allonychiurus foliatus (Rusek, 1967) and Allonychiurus mariangeae (Thibaud & Lee, 1994) are re-allocated to Thibaudichiurus. List and identification key to the world species of the genus are given.


Introduction
Th e genus Allonychiurus Yoshii, 1995 includes 23 species according to Bellinger et al. (2010). Th ey are distributed in Asia, Europe and America. However, as stressed by Sun et al. (2009), generic assignment of most of these species is disputable. To improve this confusing situation, we re-examined all available taxonomic descriptions and type specimens of several species. We redefi ned the genus accordingly. As a result, fi ve species are translocated to other genera and four are considered as incertae sedis. A new species discovered in China, Allonychiurus antennalis sp. n., is described.

Discussion
Th e genus Allonychiurus is very similar to Onychiurus Gervais, 1841 diff ering from it by a furcal area with 4 small posterior chaetae arranged in two rows versus arranged in one row. It is also the only diff erence between Th alassaphorurini and Onychiurini. Th e attempt to restrict the genus Allonychiurus to species with 11 distal chaetae on tibiotarsus (Sun et al. 2009) versus 9 in Onychiurus cannot be retained on current available evidence, as discussed below.

Th e problem of species assigned to Allonychiurus
Th e genus Allonychiurus was described by Yoshii (1995) as a subgenus of Onychiurus Gervais, 1841, to include species of the fl avescens-group of Paronychiurus previously recognized by Weiner (1989). Th is last author upgraded it to genus level in 1996, characterizing it mostly on the basis of its furcal area similar to that of Th alassaphorura Bagnall, 1949, and its post-antennal organ with several compound vesicles. Recently, Sun et al. (2009) restricted the defi nition of Allonychiurus to species with 11 chaetae in the distal whorl of tibiotarsus (a character erroneously stated as being drawn from the Weiner 1996 diagnosis); according to this conception, only four species (out of the 24 species listed at this time on the Janssens and Christiansen website at http://www.collembola.org) could be confi rmed as Allonychiurus (fl avescens, jongaksanensis, shanghaiensis and shinbugensis), in addition to A. megasomus that Sun et al. (2009) described in their paper. Th e authors also reallocated tentatively two species, A. edinensis (Bagnall, 1935) and A. subedinensis (Arbea & Jordana, 1985) to the genus Spinonychiurus Weiner, 1996, a move formally confi rmed by Kaprus' and Tsalan (2009); they stressed that 12 species did not match the genus as they defi ned it, nine because they had fewer than 11 chaetae in the distal whorl of tibiotarsus, two because they had smooth clubs in antenna III organ, and one because it had simple PAO vesicles. Th e remaining 6 species were not documented for distal tibiotarsal chaetae, and their status was considered as doubtful. In short, 80% of species assigned to Allonychiurus did not match the Sun et al. (2009) defi nition of the genus before our study.

Th alassaphorurini versus Onychiurini
A further concern is that furcal area chaetotaxy, i.e. the diagnostic character that Pomorski (1998) proposed to distinguish the tribes Th alassaphorurini, where Allonychiurus is placed, and Onychiurini, is not documented in most of the 23 species assigned to Allonychiurus by Bellinger et al. in 2010. Th ese species could belong as well to a genus of Onychiurini, like Onychiurus. In this respect, a few Onychiurus species described in the recent paper of Pomorski, Furgoł and Christiansen (2009) have a furcal area similar to that of Allonychiurus, but the authors do not formally discuss the important taxonomic implications of this fi nding. Th ey nevertheless recognize that «Many of the features he (Pomorski) used to redefi ne the genus (Onychiurus) are not given in many descriptions». A large number of species assigned to Allonychiurus and Onychiurus in Bellinger et al. (2010) need therefore to be re-examined in detail, as it is not known if they match the modern diagnoses of these genera. In parallel, diff erences between both genera as well as between Onychiurini and Th alassaphorurini have to be re-assessed.

Th e chaetotaxy of tibiotarsus
Th e use of the number of chaetae in the distal whorl of tibiotarsus as a diagnostic character to defi ne Allonychiurus deserves further comments. Th is character is not mentioned in the published descriptions of Allonychiurus by Yoshii (1995) and Weiner (1996). Bellinger et al. (2010) key out the genus as having "more than 7" chaetae in this whorl. Sun et al. (2009) characterize Allonychiurus as having 11 chaetae in the distal whorl of tibiotarsus. Actually, only six species have these 11 chaetae including the type species of the genus, A. fl avescens (though it needs to be confi rmed on type locality specimens) and the new species A. antennalis described here. Among the species listed as Allonychiurus in the web site of Janssens and Christiansen at this time, Sun et al. (2009) recognized 9 species with less than 11 distal tibiotarsal chaetae (easily seen on original drawings of A. mediasetus (Lee, 1974), and A. pseudocellitriadis (Lee, 1974), less obvious for other species). Other morphological characters are very similar between 9-and 11-chaetae species. In order to avoid the splitting of Allonychiurus in weakly defi ned entities, and given our poor knowledge of other diagnostic characters (furcal area and antenna III organ) in several species, we defi ne Allonychiurus as having 9 or 11 chaetae in the distal whorl of tibiotarsus. Th is is in line with the other large genus of Th alassaphorurini, i.e. Th alassaphorura, where distal tibiotarsal chaetae are 7 or 9 (Sun et al. 2010), suggesting that this character may have lower taxonomical value in some genera than recently thought.

Taxonomical approach
In this contribution and as a fi rst step, we address the taxonomic problems raised above in three ways. First, in order to accommodate several species that would otherwise necessitate the creation of new poorly defi ned genera, we extended the diagnosis of Allonychiurus of Sun et al. (2009) to include species with sensory clubs of antenna III organ smooth or granulated (versus only granulated), and species with 9 or 11 distal chaetae on tibiotarsus (versus only 11). Th is new defi nition is compatible with the characters of Allonychiurus extracted from the key of Bellinger et al. (2010). Second, we remove from the Allonychiurus list of Bellinger et al. (2010) nine species that do not match diagnostic characters of Allonychiurus: four are considered incertae sedis, and fi ve are reallocated to other genera. Th ird, we provisionally keep in Allonychiurus several insuffi ciently described species listed by Bellinger et al. (2010) that do not confl ict with the defi nition of the genus, but could belong as well to other genera like Onychiurus or Th ibaudichiurus Weiner, 1996; their generic assignment will have to be checked from fresh material.

Critical checklist of the world species of Allonychiurus Yoshii, 1995
In the checklist given below, an asterisk (*) indicates that species assignment requires confi rmation.

Species removed from Allonychiurus
Th alassaphorura sensilata (Th ibaud & Massoud, 1979), comb. n. Th is species was originally described from Lesser Antilles (Central America) in the genus Protaphorura and later transferred to Allonychiurus by Bellinger et al. (2010). PAO with simple vesicles undoubtedly places this species in Th alassaphorura Bagnall, 1949 according to original description, to observation of Sun et al. (2009) and to re-examination of type specimens.  Weiner (1996) is the presence of 2+2 versus l+1 pseudocelli on fi rst thoracic tergite. Th e same character is supposed to separate two other genera of Th alassaphorurini (Jailolaphorura Yosii & Suhardjono, 1992 and Th alassaphorura Bagnall, 1949), but was not considered of generic value by Sun Xin et al. (2010), as typical and closely related species of Th alassaphorura may have either 1+1 or 2+2 on this tergite. In the same way, we did not retained this character as discriminant for Th ibaudichiurus. However, Th ibaudichiurus is maintained here on the basis of its single row of manubrial chaetae posterior to dental chaetae (several in Allonychiurus) (Weiner 1996 and comm. pers.), and the presence of characteristic, thickened chaetae on the male genital plate that are not recorded in Allonychiurus species. According to Pomorski (1998) Th ibaudichiurus is also closely related to Tantulonychiurus Pomorski, 1996 from which is diff ers by modifi ed chaetae of male restricted to the genital plate and position of dorsomedian pseudoscelli on abdomen IV and V tergites; we confi rm also the diff erence suspected by Pomorski in number of distal chaetae of tibiotarsi (11 in Th ibaudichiurus,7 in Tantulonychiurus). Arrangement of chaetae on and around furcal area (but not their morphology) is identical between the two genera.

Note on species ecology and distribution
Allonychiurus occurs in a wide range of habitats. Most described species live in soil and litter of lowland areas (Weiner 1989). Th e type species of the genus (A. fl avescens) has been found in caves in Korea, but is described from soil in Japan. Th e identity of the Korean specimens and the original specimens from Japan may be questioned given the diversity of the genus (Yoshii 1995). No other location in cave habitats is mentioned in the literature for Allonychiurus, in contrast to Onychiurus which is highly diversifi ed in caves. Two species (A. pamirensis and A. tianshanicus) live at high altitude in central Asia. Two others (A. donjiensis and A. jindoensis from Korea) are coastal halophilous species (Lee and Kim 1994); their generic assignation needs however confi rmation, as this ecology and several morphological characters rather points to Th ibaudichiurus from the same habitat and same region.

Abbreviations and vocabulary used
Material. Th e codes between brackets are fi eld codes of the samples which contained the specimens, for instance (C9581).
Th e uneven axial chaeta m 0 (Sun et al. 2010) of Abd. VI tergite is named here p 0 in agreement with the literature.
S-chaetae formula is the number of S-chaetae by half-tergite from head to Abd. VI (for instance: 11/012/222120).

Key to world species of Allonychiurus Yoshii, 1995
Note. Some forms of Allonychiurus fl avescens from USA may lack pso on Th . I or are polymorphic (Christiansen and Bellinger, 1998). In the absence of more detailed information regarding other characters, they are not included in this key.