Cylindropygus ferox gen. n., sp. n.: A new member of the Cryptopygus complex (Collembola, Isotomidae) from central France

Cylindropygus, a new genus of isotomid Collembola, is described. It differs from all other genera of Isotomidae by a unique combination of characters (abdominal segments V and VI fused, eyes absent, postantennal organ present and elongate, S‐chaetotaxy, and absence of foil chaetae) and two remarkable features: a modified labium, with papillae A, B, D bearing strong spines; and a swollen, globular accp3 chaeta on Abd.V. Cylindropygus ferox sp. n. is common in forest soils of central France.


Introduction
Cryptopygus Willem, 1902 is a large genus of about 80 species distributed worldwide. As currently understood, it comes near another speciose and poorly defined genus, Proisotoma Boerner, from which it differs only by the fusion of abdominal tergites V and VI. Different isotomid genera (Hemisotoma Bagnall, Proisotomodes Bagnall and Isotomina Boerner) have been synonymized with Cryptopygus on the basis of this single feature, though they clearly differ in a number of important characters. The heterogeneity of the genus was stressed by Potapov (2001), who chose not to subdivide it due to a lack of data on most species.
In a recent paper entitled ''Do we have Cryptopygus … in Europe?'', Rusek (2002) returned to the original concept of the genus that he considers as restricted to southern hemisphere species. He restored for European species the genera Hemisotoma Bagnall, and Proisotomodes Bagnall, unduly synonymized with Cryptopygus in his opinion. Rusek's work provides a good starting point for reconsidering the whole Cryptopygus complex in the light of modern systematics and from an evolutionary perspective. In this first contribution, we describe a new genus, Cylindropygus, which has abdominal tergites V and VI fused, but does not fit any genus of the Cryptopygus complex (Hemisotoma, Cryptopygus, or Proisotomodes) in other important characters.

Comments
Cylindropygus belongs to the Cryptopygus complex of genera by the fusion of Abd.V and VI, presence of PAO, absence of anal spines and lack of morphological modification of Abd.V-VI. It differs in the following features: 1. The absence of foil chaetae on Abd.VI.
From Hemisotoma Bagnall, the new genus differs in characters 1, 3 and 6; from Proisotomodes Bagnall, in 2 and 3; from Appendisotoma Stach, in 2 and 5; from Cryptopygus sensu stricto Willem, in 5 and 6; from Dagamaea Yosii, in 3, 4 and 5. Summarizing, Cylindropygus combines the characters of different genera and the phylogenetic position of C. ferox sp. n. in the Cryptopygus complex is obscure. It also does not exhibit strong similarities with any Proisotoma sensu lato species either. Whereas Schaetae pattern of Cylindropygus body (4,3/2,2,2,3,4) looks similar to that of most species of the subfamily Anurophorinae, the combination of three S-chaetae on Abd.IV with four on Abd.V is unusual. Almost all species of the Proisotoma complex have two and four, and all species of the Cryptopygus complex have three and five. Detailed study of both complexes will be given in further publications. In our opinion, Cylindropygus is closest to the large genus Cryptopygus s. str. distributed in the Southern Hemisphere with only a few members penetrating to the Northern Hemisphere.
In addition, the type species of the new genus shows two unusual features that are probably adaptive, a cylindrical habitus and a strongly modified labial palp, unknown so far for the family.
Cylindropygus is the only endemic Collembolan genus of the Massif Central in France. It was unexpected to find such a phylogenetically isolated taxon in this mountain range, which has a soil fauna notoriously lacking endemic elements, specially in lowland forest.

Type deposit
Holotype and three paratypes mounted in Marc-André II and 30 paratypes in alcohol deposited in the Muséum national d'Histoire naturelle de Paris. One paratype mounted in Marc-André II and five paratypes in alcohol deposited in the collection of Moscow State Pedagogical University.

Description
Body length 0.65-0.80 mm. Habitus perfectly cylindrical, elongate (Figure 1). Abd.V-VI fused, rounded, V+VI slightly shorter than III. Antennae shorter than head. Entirely white. Integument covered with small elementary hexagonal grains, larger on head.
Dorsal mesochaetae slightly curved, acuminate, smooth; longer on Abd.IV-V where they are weakly but distinctly serrated on one side; not shortened in axial part of tergites. Macrochaetae straight, thin, long and acuminate. S-chaetae thin and rather long, but shorter than nearby mesochaetae.
Mandible slightly asymmetrical, with four teeth, the distal much smaller than the antedistal. Outer maxillary lobe with four sublobal hairs, palp bifurcate ( Figure 2). Labral formula 4/5,5,4, with chaetae of the two anterior rows thickened (Figure 3). Labium with three proximal and four baso-median chaetae, full set of guards and papillae. Labial palp  papillae A, B, D armed with strong teeth; C with a weaker one, and E with a normal hair (Figure 4).
Eyes absent. PAO long, curved and sclerotized ( Figure 6). Antennae: Ant.I with two rather short ventro-external S-chaetae of equal length, one thicker; 11 ordinary chaetae; and two basal microchaetae. Ant.II with one thin ventroexternal S-chaeta, 17 ordinary chaetae and three basal microchaetae. Ant.III organ like usual, with five S-chaetae. Ant.IV with a rather large organite with its guard chaeta short. Several clearly recognizable S-chaetae on Ant.IV, four or five rather strongly thickened, three or four lesser thickened and several thin (Figure 7).

Etymology
The species name refers to the strong teeth of the labium.

Comments
Due to habitus, C. ferox sp. n. is readily recognizable among European Isotomidae.

Ecology
The species is widespread, though not abundant, in forest soils of the mid-part of the Massif Central, France.