Hypogastrura yosii Stach, 1964

Babenko, Anatoly, Efeykin, Boris & Bizin, Mikhail, 2020, Three new and one little-known species of Hypogastruridae (Collembola) from Russia's northeast, ZooKeys 1005, pp. 1-20 : 1

Hypogastrura yosii Stach, 1964 Figs 24-29

Hypogastrura sheyangensis Syn.: Hypogastrura sheyangensis Jiang, Tang & Chen, 2007.

Material.

Russia • 3 ♂♂, 9 ♀♀ (slides) and ~ 50 specimens (alcohol); Kuril Islands, Kunashir; 43°42.91'N, 145°33.20'E; wrack beds; August 2017; K. Makarov leg. Several specimens from this material were sequenced (Table 1 ). Their partial COI genes were amplified and deposited in the GenBank under the sample ID: KY066784-KY066786.

Taxonomic remarks.

Stach’s (1964) original description of H. yosii was based on two specimens collected in forest sites in eastern China. Its real position within the genus had remained unclear until it was recently redescribed from the types ( Jia et al. 2011) and synonymised with H. sheyangensis Jiang, Tang & Chen, 2007. The latter species was known from the coastal wetlands of the same region. Specimens from Kunashir Island fit rather well with the existing descriptions, but are significantly smaller, 0.7-0.9 mm vs. "up to 1.5 mm" in Chinese specimens.

Both recent descriptions ( Jiang et al. 2007; Jia et al. 2011) considered H. yosii as being most similar to two Nearctic species, viz. H. matura (Folsom, 1916) and H. utahensis (Wray, 1953) (now a junior synonym of H. promatro (Wray, 1950) [see Bernard 2015]). This opinion was mainly based on the absence of seta p4 on Abd.4. In fact, this seta, set anteriorly to the p-row (almost aligned with m-setae), may occasionally be absent on one or both sides in many species of the Hypogastrura manubrialis -group. This is also rather frequent in specimens of H. yosii from Kunashir Island (Fig. 24 ). In our view, H. yosii is closely related to the widespread H. manubrialis (Tullberg, 1869). Apart from the absence of a seta m2 on Th.2 (one of the most notable peculiarities of H. manubrialis ), the similar number of sensilla on Ant.4, the relatively large PAO with secondary projections at the base of the lobes, and the short anal spines, both species are characterised by an almost identical structure of the maxillary head (except for lam.6, which in H. manubrialis has no denticles in the central part) (Fig. 25 ) and the absence of a a1 guard on the labial palp (Fig. 26 ). This short guard is present in most congeners studied, but not in the Hypogastrura manubrialis group, in which it is present in only some species: H. arctandria Fjellberg, 1988, H. assimilis (Krausbauer, 1898), H. vernalis (Carl, 1901), and H. promatro , but it is absent from others: H. manubrialis , H. yosii , H. serrata ( Ågren, 1904), and H. rangkuli Martynova in Martynova and Chelnokov 1975. Meaningful differences between H. yosii and H. manubrialis appear to be limited by maxillary lam.6 (see above), the presence of seta p’ on Ant.1 in H. yosii (a variable character in specimens from Kunashir, where only six of ten specimens examined show p’ seta on at least one antenna) and a characteristic mucro shape, i.e., a long and slender mucro without clear lateral lamellae in H. manubrialis or a mucro with an "upturned apex and [clear] outer lamella" in H. yosii (Figs 27-29 ).

Figures

Figures 24 - 29. Hypogastrura yosii Stach, 1964 24 dorsal chaetotaxy of Abd. 4 - 6 25 maxillary head 26 labial palp 27 dens and mucro, lateral view 28 dens and mucro, dorsal view 29 dens and mucro, ventral view. Scale bars: 0.1 mm (24), 0.01 mm (25 - 29).