Disjunct distribution of Szeptyckiella gen. nov. from New Caledonia and South China undermines the monophyly of Willowsiini (Collembola: Entomobryidae)

Morphology of scales is an important taxonomical character at all levels of Entomobryidae taxonomy. A new scaled genus of Collembola, Szeptyckiella gen. nov., and three new species are described: Szeptyckiella boulouparica sp. nov. and Szeptyckiella sinelloides sp. nov. from New Caledonia, and Szeptyckiella lii sp. nov. from South China. The genus, assigned to Willowsiini, is characterized by pointed scales on the body, eyes and pigment absent, antennal apical bulb absent, dens lacking spines and scales, and bidentate mucro with a short basal spine. It is closest to Hawinella from Hawaii but the latter possesses a falcate mucro. However, its morphological characteristics and its disjunct distribution raise a number of problems. Its widely disjunct distribution is difficult to explain in terms of palaeobiogeographical or more recent dispersal events. The new genus is similar to Sinella without consideration of scales, although both genera are placed in different tribes following the current supra-generic classification of Entomobryidae. We discuss other cases of paired genera differing only by the presence or absence of scales, and placed in either Willowsiini or Entomobryini. On this basis, we assume that scale presence could independently occur in the former tribe, questioning the monophyly of the tribe Willowsiini.


Introduction
Scales occur in most Tomoceroidea and Entomobryoidea species of Collembola, with their morphology (shape and surface sculpture) highly diversified among Entomobryidae. Classification of the subfamily Entomobryinae sensu Soto- Adames et al. (2008) relies on the distribution and morphology of scales and, at species level, scale morphology is important in the taxonomy of the genus Willowsia. Denis (1941) recognized two groups in scaled entomobryids, Siraeformes and Lepidocyrtiformes respectively without and with dental scales. Yosii (1961) erected Seirinae (sensu Lepidocyrtiformes Denis) including the species with accessory chaetae around bothriotricha and retained Siraeformes in Entomobryinae. In 1979, Szeptycki further divided Seirinae into Seirinae and Lepidocyrtinae based on tergal chaetotaxy and scale morphology. Yoshii and Suhardjono (1989) demoted the subfamilies Seirinae and Lepidocyrtinae into the tribes Seirini and Lepidocyrtini, while establishing a new tribe Willowsiini sensu Siraeformes Denis. Four tribes, Entomobryini, Willowsiini, Seirini and Lepidocyrtini, are now included in Entomobryinae, with only Entomobryini lacking scales (Soto-Adames et al. 2008). A new genus of Willowsiini from New Caledonia and South China is described here and species from the two areas are compared. The problems raised by the discovery of this new taxon and the use of scales in the taxonomy of the family Entomobryidae are discussed.

Material and methods
Specimens were mounted after clearing in lactic acid under a coverslip in Marc André II solution, and were studied using a Leica DMLB microscope. Photographs were taken with a ProgRes camera mounted on a Leica DMLB microscope and were enhanced with Photoshop CS2/PC (Adobe Inc.). The dorsal and ventral chaetotaxy of head and the Ant. III organ are described after Chen and Christiansen (1993). Dorsal body chaetae are designated following Szeptycki (1979) and Zhang et al. (2011b). The number of macrochaetae is given by halftergite in the descriptions. Material is deposited in the collections of the Muséum national d'Histoire naturelle (MNHN), Paris, France and of the Department of Entomology, College of Plant Protection, Nanjing Agricultural University (NAU), Nanjing, China.

Diagnosis
Medium size (up to 1.42 mm) entomobryid. Eyes and pigment absent. Scales present on the body, coarsely striate with striations very short, and leaf-like with tip pointed; scales on ventral side of manubrium present but narrower than those on body. Polymacrochaetotic chaetotaxy. Prelabral and labral chaetae 4/5, 5, 4, all smooth. Labrum margin with inverted median U-form intrusion. Chaetae mel 1 l 2 of labium smooth. Five papillae of labial palp with 0, 5, 0, 4, 3 guard chaetae. Subapical chaeta of maxillary outer lobe slightly stronger than apical one; three smooth hairs on sublobal plate. Four antennal segments (I and II not subdivided, IV not annulated
Abd. IV 2.3-3.5 times as long as Abd. III along dorsal midline. Trochanteral organ with eight or nine smooth spiny chaetae ( Figure 2H). Inner outstanding mac located at about 0.4 distance from base, ciliate, thick and tapered ( Figure 2I). Ungual unpaired inner tooth extremely tiny. Unguiculus with a large outer tooth ( Figure 2J). Ventral tube anteriorly with one small and one large ciliate chaeta on each side ( Figure 2K); posteriorly with four apical smooth and two weakly ciliate proximal chaetae ( Figure 2L); each lateral flap with four smooth chaetae ( Figure 2M). Manubrial plaque with one pseudopore and two ciliate chaetae ( Figure 2N). Distal smooth part of dens 1.7 times as long as mucro ( Figure 2O). Male genital plate papillate and details not seen clearly.

Ecology
In litter and soil of a stand of Araucaria, in a thalweg.

Etymology
Named after the type locality.

Remarks
This species is characterized by relatively short antennae (less than twice as long as head), absence of X 2 on ventral side of head, four cephalic sutural mac, modified accessory mic of bothriotricha, reduced number of mac on Th. II, one mac (m4) and one S-chaeta on Abd. I, six short S-chaetae on Abd. IV, and four S-chaetae on Abd. V. Differences with other species of the genus are summarized in Table 1.

Types
Holotype. Female on slide, New Caledonia: Province Sud: Rivière Bleue, 10 December 1995, lowland forest, litter, Berlese extraction, L. Deharveng and A. Bedos leg. . Paratypes. Three females on slide and eight in alcohol, same data as holotype. Holotype and eight paratypes (two on slide and six in alcohol) in MNHN, three paratypes (one on slide and two in alcohol) in NAU.

Description
Body length 1.42 mm. Ground colour pale yellow in alcohol ( Figure 4A). No eyes. Most scales coarsely striate and leaf-like with tip pointed; present on Ant. I, head ( Figure 4D), tergites and ventral side of manubrium; scales of manubrium narrower.
Antenna 2.1-2.3 times as long as cephalic diagonal. Antennal segments ratio as I : II : III : IV = 1 : 2.44 : 2.22 : 3.00. Antennal chaetae mainly with seven types similar to S. boulouparica, sp. nov.; smooth straight mic at base of antennal segments, three dorsal ( Figure 4B), three ventral and one external on Ant. I and one internal, one external and one ventral on Ant. II; swollen S-chaetae absent on Ant. I, and two dorsal present on Ant. II; dagger-shaped chaetae three, four and at least six ventrally on Ant. II, III and IV respectively. Ant. III organ with chaetae 2 and 3 rod-like and feebly swollen, chaeta 5 shorter than chaeta 4 ( Figure 5A). Distal labral papillae absent. Lateral process of labial palp slightly thicker than normal chaetae, with tip reaching beyond apex of closest labial papilla ( Figure 5B). Labial base as mrel 1 l 2 , all smooth; r 0.65 as long as chaeta m; chaetae X 2 and X 3 absent, X and X 4 ciliate ( Figure 5C). Dorsal cephalic chaetotaxy same as S. boulouparica, sp. nov.
Abd. IV 3.6 times as long as Abd. III along dorsal midline. Trochanteral organ with 17 smooth spiny chaetae ( Figure 5D). Ungual unpaired inner tooth absent. Unguiculus with a large outer tooth ( Figure 5E). Ventral tube anteriorly with two or three small and one large ciliate chaeta on each side ( Figure 5F); posteriorly with four distal and four proximal smooth chaetae ( Figure 5G); each lateral flap with five smooth chaetae. Manubrial plaque with one or two pseudopores and three ciliate chaetae. Distal smooth part of dens 0.7-1.0 times as long as mucro ( Figure 4C).

Ecology
In litter of lowland forest on ultramafic rocks.

Etymology
Named after the similarity to species of Sinella.

Remarks
This species differs from S. boulouparica sp. nov. in having longer antennae, no labral papillae, longer lateral process of labial palp, ciliate X on ventral side of head, mac present on a1-3, p1, a6i and p6 on Th. III, m4p and a second S-chaeta on Abd. I, more chaetae on ventral tube and shorter distal smooth part of dens (Table 1).  on head, tergites and ventral side of manubrium, absent on Ant. I; scales on manubrium narrower ( Figure 7D). Antenna 1.35-1.54 times as long as cephalic diagonal. Antennal segments ratio as I : II : III : IV = 1 : 2.11 : 1.89 : 3.67. Antennal chaetae mainly with seven types similar to above two species; smooth straight mic at base of antennal segments (three dorsal and three ventral on Ant. I, and one internal, one external and one ventral on Ant. II); curved, thin or moderately thick (on Ant. II-IV), blunt S-chaetae (two internal and three external on Ant. II, not clear on Ant. III-IV); swollen S-chaetae absent on Ant. I, and one dorso-distal present on distal Ant. II; dagger-shaped chaetae present on ventral Ant. II-IV, one external on Ant. II and three ventral on Ant. III. Ant. III organ with chaetae 2 and 3 swollen ( Figure 8A). Labral margin without papillae. Lateral process of labial palp as thick as normal chaetae, with tip just reaching apex of closest labial papilla ( Figure 8B). Labial base as mRel 1 l 2 , R ciliate and 0.6 as long as chaeta m; chaetae X 2 and X 3 absent, X and X 4 ciliate; G [1][2][3][4] and H 3 smooth ( Figure 8C). Cephalic dorsal chaetotaxy with five sutural mac and three mac in Gr. II. Clypeal chaetae ciliate ( Figure 8D).
Abd. IV 3.1-3.6 times as long as Abd. III along dorsal midline. Trochanteral organ with 10-12 smooth spiny chaetae ( Figure 8E). Ungual unpaired inner tooth present. Unguiculus outer edge smooth ( Figure 8F). Ventral tube anteriorly with five or six small and two large ciliate chaetae on each side; posteriorly with four distal smooth and four proximal chaetae; each lateral flap with six smooth chaetae, and one smooth or weakly ciliate ( Figure 8G). Manubrial plaque with two pseudopores and three ciliate chaetae ( Figure 8H). Distal smooth part of dens 2.4 times as long as mucro ( Figure 7B).

Ecology
In litter of forest.

Etymology
Named after the collector Zhao-Hui Li.

Remarks
This new species differs from other species of Szeptyckiella in having ciliate R and H 1 , 2 and 4 on ventral side of head, smooth outer unguiculus edge and abundant tergal chaetotaxy ( Table 1). The arrangement of S-chaetae on Abd. V is similar to that of most entomobryids.

Problems raised by the new genus
The discovery of the new genus Szeptyckiella raises a number of problems. First, its species have a widely disjunct distribution. It is present in South China and New Caledonia but unknown in the areas between. No other collembolan exhibits such a disjunct distribution and it cannot readily be accounted for by any known palaeobiogeographical scenario. Three explanations can be envisaged: introduction by humans into China, convergent morphological evolution from a different stock of Entomobryidae, or a gap in our knowledge of distribution. The first hypothesis is weakly supported: the Chinese species (S. lii) is rare, quite different from the New Caledonian species and human exchange between China and New Caledonia has been, and is, extremely limited. There are very few introduced species shared between these regions that live outside human settlements, and all specimens of Szeptyckiella were collected in areas that were not strongly anthropized. The second hypothesis is that of evolutionary convergence. The similarity between Szeptyckiella species concerns scale shape and sculpture, but their chaetotaxic patterns recall those of the large, widespread genus Sinella, which is frequent and diversified in both regions and found in similar soil habitats. However, the same basic patterns are observed in other genera (e.g. Coecobrya; see Zhang et al. 2009aZhang et al. 2011b and may instead be plesiomorphic. In the absence of phylogeny, it is impossible to confirm the convergence hypothesis. The third possibility, that of a sampling gap, remains conceivable. Entomobryidae have been described from many areas between China and New Caledonia, but mostly from atmobiotic habitats. However, our own collections of soil fauna across the whole of Southeast Asia have not provided anything that approaches Szeptyckiella morphologically. The presence of scales in a genus otherwise very similar to Sinella is also problematic. Based on the current supra-generic classification of Entomobryidae (Soto-Adames et al. 2008), this character alone (scales on body but not on dens) places Szeptyckiella in a different tribe to that of Sinella. But the species of the new genus share many features with indigenous Sinella species except for the presence of scales.
In New Caledonia, the two species of Szeptyckiella have the same distinctive characters as indigenous species of Sinella (unpublished data): ungual unpaired inner tooth absent or extremely tiny; outer large tooth on unguiculus always present; tibiotarsal tenent hair pointed; two medio-medial (m1, m1i) and one medio-lateral (m4) mac on Th. II half-tergite; no more than four mac on Abd. I half-tergite; two (m3, m3e) mac in set m3+ on Abd. II half-tergite; one central (m2) and two lateral mac (pm6, p6) on Abd. III half-tergite (am6 as mic); four or more short S-chaetae on Abd. IV half-tergite; and 4 + 4 S-chaetae on Abd. V. The characters cited for Abd. III and Abd. V that are shared by both Szeptyckiella and Sinella species from New Caledonia can be considered the most characteristic features separating them from other entomobryid species.
Similarly, Szeptyckiella lii from South China is similar to several Chinese species of Sinella in having smooth outer edge of unguiculus, a more abundant tergal chaetotaxy, and 3 + 3 S-chaetae on Abd. V.
All of these similarities suggest that scales may have appeared to be independent between the Szeptyckiella of China and those of New Caledonia, and the new genus distribution favours this hypothesis. The discovery of Szeptyckiella tends to undermine the validity of Entomobryini and Willowsiini.

Scales in the classification of Entomobryinae
Among the three scaled tribes of the subfamily, Seirini and Lepidocyrtini have relatively conserved scale morphology and their monophyly is widely accepted. Willowsiini is well defined by the absence of dental scales, although it possesses diverse scale types (Zhang et al. 2011a). The monophyly of Willowsiini, to which the new genus formally belongs, has never been verified, but evidence that some of its species may be more related to those of other tribes brings into question its validity and limits (Yoshii and Suhardjono 1989;Zhang et al. 2011a). Similarities between Szeptyckiella (Willowsiini) and Sinella (Entomobryini) imply possible convergence. A broader review provides several pairs of genera consisting of scaled (Willowsiini) and unscaled (Entomobryini) genera that are very similar, except in scale morphology (Table 2). For example, Homidia and Sinhomidia share an "eye-brow" mac on anterior Abd. IV, the subapical mucronal tooth larger than the apical one, a bilobed bulb on antennal apex, and smooth labial chaetae e and l 1 . Similarly, Coecobrya and Hawinella have no or reduced eyes, a falcate mucro and no antennal apical bulb. The first-instar larval chaetotaxy of both tribes was shown to be almost identical by Szeptycki (1979), who did not formally isolate "Willowsiini" from other Entomobryinae, writing: "For practical reason in the subfamily Orchesellinae and Entomobryinae I combined the species without scales (chaetosae) and those with scales (lepidosae) into separate though not formal groups". The placement of Szeptyckiella within Willowsiini should be therefore considered as provisional. We expect that a phylogenetic analysis of Entomobryinae will solve this important taxonomic and evolutionary problem.