Pseudachorutes cf. isawaensis Tamura, 2001

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 : 376-378

Pseudachorutes cf. isawaensis Tamura, 2001

Figs 72–75

Examined material. Russia: 1 female, Republic of Sakha (Yakutia), Suntar-Khayata Mt. Range, upper reaches of Kyubyume River , vicinity of «Vostochnaya» weather station, 63°14.45’N 139°37.88’E, Dryas plant association, 1480 m alt., 28 July 2002. O. Makarova leg. ; 1 female, 1 male and 2 juveniles, Far East, Southern Primor’e , ~ 30 km SE of Chuguevka, mixed forest, 44°1.32’N 134°9.02’E, ~ 500 m alt., 11 August 2017 ; 1 male, 1 female and 2 juveniles, Sikhote-Alin State Nature Reserve, Brusnichnaya River , mixed (cedar, poplar, spruce, elm, white fir, birch, etc.) forest in valley, 45°38.9’N 137°0.58’E, ~ 200 m alt., 6 August 2017 ; 2 females, Khabarovsk Territory, Komsomolsk State Nature Reserve, Gorin River , mixed coniferous-broadleaf forest, rotting wood, 50°44.25’N 137°25.43’E, ~ 250 m alt., 10 August 2018. All N. Kuznetsova, A. Kuprin & A. Geraskina leg.

Main diagnostic characters: Medium sized species. Labrum with 4/2334 setae, labium with 3 proximal setae and seta L, basomedial part of labium with 3 setae (f—absent), its basolateral part with 4 setae, 4 perilabial setae present. Head with both a0 and d0, Th. I with 3+3 setae, occasionally with 4+3 or 4+4, Th. II with a2, Th. II–III with 4 ordinary setae (a3, a4, m4 and p4) additionally to S in dorso-external group, Abd. I–III with setae a3, m3 and m 4 in front of p3 and p4 (=S). Mucro with basal «swelling». Each anal lobe with 3 hr-setae.

Description based on the examined material. Medium-sized species with general appearance typical of genus with expanded body in the region of Abd.II–III ( Fig. 72 ), length of adults (without antennae) up to 1.3 mm, but usually ranged between 0.75 and 1.00 mm. Colour grey-blue, rather dark. Tegument granulation coarse and uniform.

Antennae slightly shorter than head, Ant. III–IV fused dorsally, ventral separation well marked. Ant. IV with typical trilobed apical vesicle, external ms, subapical or and seta i present; dorsal side of Ant. IV with six differentiated curved sensilla (S1–S4, S7–S8), ventral side with few short pointed or truncate setae. Antennal organ of Ant. III typical, inner sensilla small, sgv not especially longer than sgd, ventral ms present. Ant. I–II with 7 and (12)13 setae, respectively.

Head with 8+8 subequal ocelli. PAO rounded or slightly elliptic, consisting of 8–12 vesicles, about as large as nearest ocellus B, ratio 1.0–1.1: 1. Buccal cone elongate. Maxilla styliform, mandibular shape not defined. Distal edge of labrum rounded, number of labral setae as follows: 4/2334. Main part of labium with three proximal ordinary setae (B-seta absent), distal seta L and two tiny labial organites present; submentum with three setae (f-seta absent), mentum with usual set of four setae ( Fig. 73 ). Perilabial area with 4+4 setae.

Dorsal setae short and fine ( Fig. 72 ), sensilla 1.5–2.5 times longer than ordinary setae, their number as usual, 22/11111. Main characteristics: head with both unpaired a0 and d0, Th. I usually with 3+3 setae (but specimens with 3+4 and even 4+4 setae also seen), Th. II with a2-setae, dorso-external group with three setae (a3–a4, m4) in front of p3–p4, lateral ms present. Th. III identical, but without a2 and ms. Abd. I–III usually with three setae (a3, m3–m4) in front of p3–p4. Abd. V without p2 as usual.

Thoracic sterna without setae. Ventral tube with 4+4 setae, no seta on sternum of Abd. I, Abd. II with 4+4 ventral setae, Abd. III with 6–9 setae. Tenaculum with 3+3 teeth as usual. Furca not especially long. Manubrium with 9–10+9–10 setae on main part, 4 setae on each basolateral lobe and 2 basal setae in line. Dorsal side of dens with six setae and uniform coarse granulation, hyaline field on its ventral side large. Mucro about as long as ½ dens, basally with high and short lateral lamella, i.e. «basal swelling» present ( Fig. 75 ). Each anal valve with three tiny hr-setae.

Legs I–III with 1, 2, 2 setae on upper subcoxae, 0, 2, 2 setae on lower subcoxae, 3, 8, (6)7 setae on coxae, 6, 6, 6 on trochanters, 13, 12, 11 setae on femora and 19, 19, 18 setae on tibiotarsi. Unguis rather long and narrow with clear inner tooth in basal third of inner edge, lateral teeth invisible ( Fig. 74 ).

Remarks. We were not able to identify this form for sure. Two comparable species having the same structure of labium, almost identical chaetotaxy and similar mucro with a «basal swelling» as in our form, are known in the region, i.e. P. isawaensis Tamura, 2001 ( Japan) ( Table 1) and P. jianxiucheni Gao, Yin & Palacios-Vargas, 2008 ( China) . The described differences between them are as follows: the former species is larger (1.6 mm in P. isawaensis vs 1.05 mm in P. jianxiucheni ), has relatively longer mucro (0.6 of dens in P. isawaensis vs 0.5 in P. jianxiucheni ), only one maxillary lamella (vs two in P. jianxiucheni ), mandibles with two teeth (vs four teeth in P. jianxiucheni ), VT with 3+3 setae (vs 4+ 4 in P. jianxiucheni ), Ant. IV with only 5 dorsal sensilla (vs usual 6 in jianxiucheni ) and 4+4 setae on Th. I (vs 5+ 5 in P. jianxiucheni ). Despite the large number of these differences, most of them may well be ordinary aberrations. The most significant of them, in our opinion, are the shape of the mandibles and the number of setae on the Th. I, which are usually not variable. Unfortunately, the mandibles are not visible in our material, while the number of setae on Th. I varies (usually 3+3, but sometimes 3+4 or even 4+4) being closer to that of P. isawaensis (4+4).

The most specific feature of P. cf. isawaensis described above is the structure of the labium, namely the absence of the microseta f on its basomedian part (submentum), while maintaining all the usual four setae on the mentum (we prefer to use traditional Massoud’s nomenclature (1967), which seems to be preferable for the studied genus than that of D’Haese (2003)). In other words, ten ordinary setae (3+3+4) are present as a whole ( Fig. 73 ). Contrary, the labium with eleven setae were figured for both P. isawaensis and P. jianxiucheni (see fig. 9 in Tamura 2001 and fig. 16 in Gao et al. 2008) which adds further uncertainness although it is quite possible that one of the basal setae on these figures belong to the perilabial area. The number of labral setae is also different (4/ 2334 in P. cf. isawaensis vs 4/ 2332 in the original description of P. isawaensis ). More studies are obviously needed to clarified the status of this Far Eastern form.

Description. The species, originally described from Japan, appears to be widespread in the eastern parts of Russia being recorded from such remote areas as central Yakutia and Southern Primor’e.

Figures

FIGURES 72–75. Pseudachorutes cf. isawaensis Tamura: 72, dorsal chaetotaxy; 73, labium; 74, unguis and tibiotarsus of leg III; 75, dens and mucro. Scales: Figs 72 = 0.1 mm, 73–75 = 0.01 mm.