Pseudachorutes boerneri Sch ӧtt, 1902

Babenko, Anatoly, Kuznetsova, Natalia, Nakamori, Taizo & Shveenkova, Yulia, 2021, A review of Pseudachorutes Tullberg, 1871 (Collembola, Neanuridae) from the East Asia, with description of six new species, Zootaxa 4938 (4), pp. 351-391 : 368-370

Pseudachorutes boerneri Sch ӧtt, 1902

Figs 53–60 , Table 1

Examined material. Russia: 1 female, Khabarovsk Territory, Komsomolsk State Nature Reserve , spruce forest in valley, forb-fern association, 50°43.7’N, 137°23.23’E, ~ 100 m alt., pit-traps, 3–11 August 2018. O. V. Kuberskaya leg. ; 1 female juvenile, same region, but Lazo District, Sikhote-Alin, tributaries of Malyi Katen River , coniferous forest, wood, 08 July 2019. A. Brinev leg. ; 1 female pread., Southern Primor’e, Chuguev District, National Park «Zov Tigra», Mount Oblachnaya , Ussuri River valley , 43°36.04’N 134°11.58’E, ~ 550 m alt., mixed forest, litter, 19–20 September 2018. A. Kuprin leg. ; 3 male, Republic of Sakha (Yakutia), vicinity of Yakutsk [~ 62°03’N, 129°31’E], larch forest, under bark of dead tree, 16 July 1997. M. Potapov & N. Kuznetsova leg.

Main diagnostic characters. Medium sized species. PAO rounded with few (6–7) lobes. Buccal cone blunt, four prelabral and 11 labral setae, i.e. 4/2324, totally, labium with full number of setae [12] and without seta L or labial organites, 5 setae in perilabial area. Dorsal chaetotaxy rich with three setae in front of setae p3–p4 on Th. II–III and with ordinary setae becoming thicker, truncate and distinctly knobbed towards abdominal tip. Dens with only 5 setae, mucro with lateral lamella almost reaching the tip. Two hr-setae present on each anal valve.

Description of specimens from the East Palaearctic. Length (without antennae) 1.2 mm. Colour dark blue, almost black. Tegument granulation uniform and not especially coarse.

Antennae slightly shorter than head, Ant. III–IV fused dorsally, ventral separation well marked. Ant. IV with simple apical vesicle, external ms, subapical or and seta i present; dorsal side of Ant. IV with six curved differentiated sensilla (S1–S4, S7–S8), ventral side with only few short sensilliform setae. Antennal organ of Ant. III typical, inner sensilla small, sgv subequal or only slightly longer than sgd, ventral ms present. Ant. I–III with usual 7 and 12 setae, respectively.

Head with 8+8 subequal ocelli. PAO rounded, consisting of six vesicles ( Fig. 55 ), about as large as nearest ocellus B. Buccal cone elongate. Maxilla styliform with two tiny apical teeth and membranous lamella, mandibles thin, with two main teeth, apical one split into several branches. Distal edge of labrum rounded, number of labral setae as follows: 4/2324 ( Fig. 57 ). Main part of labium with four proximal setae, spine-like seta L and labial organites invisible; submentum and mentum with usual 4+4 setae ( Fig. 56 ). Perilabial area with 5+5 setae, distinctly differentiated in length.

Dorsal setae on thorax short and rather strong, becoming thicker, truncate and distinctly knobbed towards abdominal tip ( Fig. 54 ), sensilla thinner but not especially longer than ordinary setae, their number as usual, i.e. 22/11111. Dorsal chaetotaxy as in Fig. 53 . Main characteristics: Head with only one unpaired seta d0. Th. I with 3+3 setae. Only Th. II with a2-setae and lateral ms, dorso-external group on both Th. II–III with 3 setae (a3–a4, m4) in front of p3–p4. Abd. I–III with 3 setae (a3, m3–m4) in front of p3, S (=p4) displaced laterally. Abd. V without p2 as usual, a2 present or absent.

Thoracic sterna without setae. Ventral tube with 4+4 setae, no seta on sternum of Abd. I, Abd. II with 5+5 ventral setae, Abd. III with 10–11 setae on each side. Tenaculum with 3+3 teeth as usual. Furca with all usual parts, dorsal side of dens with five setae, mucro hooked at apex, about as long as 1/3 dens, with long lateral lamella almost reaching tip ( Fig. 60 ). Each anal valve with two tiny hr-setae.

Legs I–III with 1, 2, 2 setae on upper subcoxae, 0, 2, 3 setae on lower subcoxae, 3, 7, 7 setae on coxae, 6, 6, 6 on trochanters, 12, 12, 11 setae on femora and 19, 19, 18 setae on tibiotarsi. Distal whorl on Ti I–III with 6, 7, 7 distinctly clavate setae ( Fig. 58 ): A1 much thicker than others, with large knob at apex, setae A2, A3, A6, A7, T2 and T3 (only on Ti II–III) also clavate, but weaker. Setae A4, A5, T1, T4 and T3 on Ti I short and acuminate. Unguis with small tooth in upper third of inner edge, lateral teeth invisible.

Remarks. The above description of this well-known «European» species is based on samples collected in several remote areas of the eastern Palaearctic, from Yakutia to southern Primor’e. Consequently, this species is clearly aboriginal, and not an introduced form for the Far East, as we first assumed. Due to the specific tibiotarsal chaetotaxy and knobbed abdominal setae P. boerneri is one of the most easily recognized species of this genus. Previously, its published records was limited to Europe where the Smolensk Region was the easternmost point of its range ( Potapov & Kuznetsova 1997). On the territory of Eastern Europe, this species was also found in the southern and eastern parts of the Arkhangelsk Region, as well as in the Middle Volga region̅̅in the Mordovian State Reserve (our unpublished data). Nearctic records obviously belong to a different species (see Christiansen & Bellinger 1980).

The above description almost completely coincides with the most recent description of this species ( Fjellberg 1998). There is only one notable difference: in Scandinavian specimens of P. boerneri setae T3 on all legs are only insignificantly weaker (thinner, less knobbed) than T2, foreleg does not differ from others (A. Fjellberg, person. comm.) whereas, in all studied specimens from the eastern Palaearctic, this seta is short and pointed on the leg I ( Fig. 58 ). Unfortunately, this character seems to be age dependent and therefore may not be particularly reliable. We were able to study two specimens of this species from the European part of Russia (Smolensk Region) and found that seta T3 on leg I is short and pointed in juvenile and becomes longer and knobbed in more mature individual ( Fig. 59 ). Therefore, we prefer to consider Far Eastern specimens as conspecific to the European ones, until the opposite is proved by further studies.

The only more or less comparable species previously known in the region under study is P. dalensi from North Korea, which however has a smaller number of clavate setae on tibiotarsi (4–4–3) and less complete dorsal chaetotaxy.

Jordana et al. (1997) transferred P. boerneri to the genus Pratanurida Rusek, 1973 (see www. collembola.org), which was created to include Pseudachorutes -like species with a partial reduction of furca. In our opinion, this transfer is poorly substantiated, and the border between the two genera is now too formal to reflect their real relations (see also discussion in Fjellberg 1985, p. 76).

Distribution. Palaearctic.

Figures

FIGURES 53–60. Pseudachorutes boerneri Schӧtt: 53, dorsal chaetotaxy; 54, Abd. V–VI; 55, PAO and ocelli; 56, labium; 57, labrum; 58, left tibiotarsus of leg I (Far East); 59, ibid. (Smolensk Region), 60, dens and mucro. Scales: Figs 53 = 0.1 mm, 54–60 = 0.01 mm.