Taxonomy of the Cryptopygus complex. II. Affinity of austral Cryptopygus s.s. and Folsomia, with the description of two new Folsomia species (Collembola, Isotomidae)

Abstract Folsomia minorae sp. n. and Folsomia australica sp. n. are described from New Zealand and Australia, respectively. Their possible affinity to two different groups of Cryptopygus sensu stricto is discussed. Attention is paid to the variability of sensillary patterns of the genital segment in Cryptopygus: mainly, all s-chaetae are subequal, but in more advanced forms the dorsal triplet, lateral duplet or either of them become macrochaeta-like in length. Cryptopygus ulrikeae (= Folsomia ulrikeae Najt & Thibaud, 1987), comb. n. is given a new generic position.


Introduction
The genus Cryptopygus  sensu stricto has not received its modern generic diagnosis and most of its "austral" species need to be revised (Rusek 2002, Deharveng et al. 2005, Jordana et al. 2009, Potapov et al. 2013, Greenslade 2015. Several species related to C. antarcticus  (the type species of Cryptopygus) are common in the high latitudes of the Southern Hemisphere and form a clear taxonomic group. They clearly differ from other genera of the Cryptopygus complex that are found in more northern areas (tropical and further into the Northern Hemisphere). In this paper we temporarily define Cryptopygus s.s. as having 3 and 5 s-chaetae on Abd IV and V respectively, s-chaetae in mid-tergal position on body tergites, and having no differentiated foil-chaetae at the end of the abdomen. Whilst hemispheric distribution patterns of certain Collembola genera have been well documented (e.g. Holarctic for Tetracanthella Schött, 1891, see Deharveng 1987, this group of "austral" Cryptopygus (Cryptopygus s.s. below) can be considered a geographical equivalent of the mostly Holarctic genus Folsomia . Although occurring in different hemispheres, both genera show an increasing diversity towards the poles, a similar set of life forms and play similar ecological roles in collembolan communities, which are more evident in polar zones. This geographical segregation is even further complicated by the movement of a few Cryptopygus s.s. and Folsomia to the opposite hemisphere. Until now, at least two "apparent" members of Cryptopygus s.s., C. clavatus (Schött, 1893) and C. roberti (Fjellberg, 1991) are known from areas of the North Atlantic. Despite the strong similarity between these two forms and the main group of "austral" Cryptopygus the final generic position of clavatus and roberti remains unresolved. The state of a few native "austral" members of Folsomia is more obscure as important characters are lacking. Here we present two apparently native and new species from the Australian region. They are described and compared with "austral" Cryptopygus s.s., the potential ancestors of "austral" Folsomia. These two species indicate that the latter genus possibly resulted from the convergent evolution of several species of the Cryptopygus s.s.
Etymology. The name is given after Maria Minor, who kindly provided some of the material on the new species.
Discussion. To date eight species of Folsomia are known from New Zealand (Greenslade 1994;2012). In addition, three species, F. parasitica Salmon, 1942, F. novaezealandiae Salmon, 1943, and F. lunata Salmon, 1943, were removed from the list as synonyms or were moved to the genus Cryptopygus (Bellinger et al. 2016). Among the valid species, five are blind, while others show different number of ocelli (8, 2 and 1, vs. 5 in F. minorae sp. n.). Very little morphological data are available for endemic New Zealand Folsomia species (F. miradentata Salmon, 1943, F. pusilla Salmon, 1944, F. salmoni Stach, 1947, and F. sedecimoculata Salmon, 1943. Particularly, figures of the furca are known only for F. sedecimoculata and F. pusilla. Both species show a more common structure of the dens (typical of the genus), which is slender and continuously narrowed, unlike in F. minorae sp. n. Clavate tibiotarsal hairs were not figured or mentioned in descriptions of New Zealand forms (present in the new species). A comparison between F. minorae sp. n. and Cryptopygus s.s. is given below.
Distribution and ecology. F. minorae sp. n. is known from three localities in South Island, New Zealand. It is probably a species restricted to mountainous areas. Diagnosis. Folsomia species with 1+1 ocelli; chaetotaxy of dens 12/6; tridentate mucro; 2 lateral s-chaetae on Abd.V clearly longer than 3 dorsal ones; 2+2 chaetae on anterior side of manubrium.
Etymology. The name is given after the geographical distribution of the new species. Discussion. Folsomia australica sp. n. resembles the only other native Australian species of the genus, i.e. F. loftyensis (Womersley, 1934) (after the redescription of Potapov and Greenslade 2010) by chaetotaxy of dens 12/6, tridentate mucro, 1+1 ocelli, ms-formula of body 10/000, differentiation of s-chaetae on Abd.V, and other characters. It differs in having 2+2 chaetae (vs. 4-5+4-5 in F. loftyensis) on the anterior side of manubrium. Juvenile specimens of the two species are probably hard to distinguish. The new species was recorded by Potapov and Greenslade (2010) as "Folsomia sp. aff. loftyensis". Folsomia australica sp. n. and F. minorae sp. n. are dissimilar indicating that the "austral " members of the genus Folsomia can also be heterogeneous, as in the Northern Hemisphere.
Distribution. Folsomia australica sp. n. is known from two localities in southeastern part of Australia (Victoria and New South Wales).
Material: South Africa ( S-chaetae patterns of Cryptopygus are probably more diverse than shown above: Cryptopygus yosii Izarra, 1965 (Argentina, after our study of a syntype) shows "3+1+1" pattern in which accp3 is thick and tubular and accp4 is short and moved to the latero-ventral position. More material on less primitive species needs to be studied to complete the generic overview. Nevertheless, s-patterns of Abd.V in Cryptopygus seem to be less divergent than in the larger genus Folsomia (Potapov and Greenslade 2010), while "austral" variant 4 (see above) has not been discovered in the latter genus.
The dorsal fusion or separation of genital (Abd.V) and pre-genital segment (Abd.IV) is traditionally considered to be of great taxonomic value in the classification of the subfamily Anurophorinae s.l., and the genus Folsomia is defined by the apomorphic condition of this character (fusion). Based on the available literature and our own observations, the s-chaetotaxy of "austral" Cryptopygus s.s. shows principally the same characteristics as in Folsomia, particularly 4,3/2,2,2,3,5 set and arrangement of s-chaetae on Abd.V. The more adaptive characters (furca, ocelli, etc.) vary considerably within both genera. Therefore Abd.IV-V fusion seems to be the only apomorphic character that separates Folsomia from Cryptopygus and the former genus can be easily derived from the latter. This key character can potentially show a high level of homoplasy and Folsomia is probably a polyphyletic or paraphyletic group. In the Northern Hemisphere, the high diversity of Folsomia makes it difficult to find an appropriate ancestor or even ancestors among known taxa. In contrast, at least three "austral" native Folsomia mentioned above show much in common with certain species of Cryptopygus s.s. Thus, all the main characters of F. minorae sp. n. (ocelli, clavate tibiotarsal hairs, outer teeth on claws, dens and mucro) indicate its close relationship to a group of species similar to Cryptopygus antarcticus (Wise 1967;Rapoport 1968, Deharveng 1981), while the characters of F. australica sp. n. are shared with several Cryptopygus species with a slender dens and tridentate mucro (see the remarks to the species). S-chaetae patterns of Abd. V in F. minorae is the same as in Cryptopygus sp. 5 from South Africa (Figs 12,23), to which this new species is, however, less similar than to the "antarcticus" group. S-pattern of F. australica and F. loftyensis is identical to Cryptopygus sp. 6 from South Africa (Figs 14, 24).
The generic position of both lineages, F. minorae and F. australica-loftyensis, can be modified in the future, depending on the increase of knowledge on the generic groups "Cryptopygus" and "Folsomia". The genus Folsomia is also very diverse in the Holarctic and consists of several species groups of which several differ in characters of great taxonomical value and may justify the status of new separate genera.