Isotomidae of Japan and the Asiatic part of Russia. I. Folsomia ‘inoculata’ group

Mikhail Potapov; Motohiro Hasegawa; Natalia Kuznetsova; Anatoly Babenko; Alexander Kuprin

doi:10.3897/zookeys.750.22764

Research Article

Isotomidae of Japan and the Asiatic part of Russia. I. Folsomia ‘inoculata’ group

Mikhail Potapov^‡, Motohiro Hasegawa^§, Natalia Kuznetsova^‡, Anatoly Babenko^|, Alexander Kuprin^¶

‡ Moscow State Pedagogical University, Moscow, Russia

§ Forestry and Forest Products Research Institute, Kochi, Japan

| The Severtsov Institute of Ecology & Evolution, Russian Academy of Sciences, Moscow, Russia

¶ Federal Scientific Center of the East Asia Terrestrial Biodiversity, Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia

Corresponding author: Anatoly Babenko ( lsdc@mail.ru )

Academic editor: Louis Deharveng

This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Potapov M, Hasegawa M, Kuznetsova N, Babenko A, Kuprin A (2018) Isotomidae of Japan and the Asiatic part of Russia. I. Folsomia ‘inoculata’ group. ZooKeys 750: 1-40. https://doi.org/10.3897/zookeys.750.22764

ZooBank: urn:lsid:zoobank.org:pub:B10B5506-EF9F-4774-80F4-BC5A776FA266

Abstract

The paper considers blind species of the genus Folsomia having two pairs of macrosetae on both meso- and metathorax and united in so-called ‘inoculata’ group, which is given a new, more laconic definition. Morphological characters important in the group’s taxonomy are discussed and a further division into four subgroups is proposed. Eight new species, i.e., F. amurica Potapov & Kuznetsova, sp. n., F. breviseta Potapov & Kuznetsova, sp. n., F. calcarea Potapov, sp. n., F. imparis Potapov & Hasegawa, sp. n., F. laconica Potapov & Kuznetsova, sp. n., F. tertia Potapov, sp. n., F. trisensilla Potapov, sp. n., and F. tubulata Potapov & Babenko, sp. n., are described. F. hidakana Uchida & Tamura and F. inoculata Stach are redescribed basing on new material, for the latter species the Stach’s individuals were also examined. A key to species of the group is given.

Keywords

α-taxonomy, Collembola , Far East of Russia, Japan, key

Introduction

The present revision is based on a vast material recently collected by the authors in various parts of the Eastern Palaearctic and older collections kindly provided by our colleagues. All used materials are deposited in the Tottori Prefectural Museum (Japan) and Moscow State Pedagogical University (Russia).

Traditional methods of morphological taxonomy were mainly used. Multi-dimensional scaling was also applied for variability analysis of widespread F. inoculata. Nine metric characters (ratios) were defined for 84 individuals from five large regions of the Palearctic (see the legend to Fig. 89). Metric characters were inferred from body measurements as following ratios: PAO length : inner edge of unguis, PAO length : width of Ant.I, manubrium length: mucro length, dens length: mucro length, dens length: macrosetae length at the end of abdomen, head diagonal : PAO length, macrosetae length at the end of abdomen : mucro length, accp2-s length : accp3-s length (Abd.V), macrosetae length at the end of abdomen : accp3-s length (Abd.V). The correlation index was used to estimate the distance between individuals. Only adults and subadults of a similar size were studied for this analysis, as well as for the species descriptions.

Abbreviations used:

Abd. abdominal segments;

alt. altitude;

Ant. antennal segments;

AO antennal organ;

bms basal ms on antennal segments;

Md, Mdl, Ml macrosetae in dorsal, dorso-lateral and lateral position;

ms micro s-seta(e) or ms-setae;

MSPUMoscow State Pedagogical University;

PAO postantennal organ;

s in the text and figures – macro s-setae or s-setae;

Th. thoracic segments;

TPM Tottori Prefectural Museum

Taxonomy

Remarks on Folsomia inoculata group

The group was firstly characterized by three basic characters, i.e., the presence of dorsal macrosetae on Th.II-III, posterior position of medial s-setae on abdominal segments, and the presence of ventral setae on Th.III (Potapov 2001).

Now it became clear that there are some important exceptions, namely three species with mid-tergal position of s-setae (breviseta sp. n., calcarea sp. n., and torpeda) and two species without ventral setae on Th.III (breviseta sp. n. and hidakana). Otherwise, all these species are obvious members of the same very characteristic East Asiatic group. This fact forces us to propose a new definition of the group: Folsomia with eyes absent, macrosetae on dorsum (= Md) of each Th. II and III present resulting in 22/333 formula, body shape tubular, head massive, PAO long and slender.

All species of the group also share several ordinary characters: four sublobal hairs on maxillary outer lobe, bifurcate maxillary palp, labral formula 4/5,5,4, not reduced edge of labrum, unguis without lateral or inner teeth, the absence of foil setae at the tip of abdomen. Therefore, we exclude all these characters from the species diagnoses given below.

Classification of the group

The group is not homogenous and its members can be classified by appearance into three types: ‘long-furcated’ common for Folsomia, ‘short-furcated’ slender cylindrical (‘tatarica’ subgroup), and stout with massive head (F. inoculata). Moreover, the group can be divided into four subgroups basing on well visible although not necessary evolutionary significant characters:

– ‘hidakana’ subgroup. It consists of the most primitive species having long furca, complete sets of s-setae and common (for the genus) number of ms-setae on body (43/22235, 10/100, as in Figs 21, 22) and without ventral setae on Th.III (Fig. 10). F. breviseta sp. n., F. hidakana.

– ‘macrochaetosa’ subgroup. Unlike the previous group, its species have ventral setae on Th.III (Fig. 9). F. amurica sp. n., F. brevisensilla, F. imparis sp. n., F. macrochaetosa, F. setifrontalis. An odd species, F. bashkira, characterized by unusual reduction of s-setae at the middle part of the body (42/11235), in other features resembles these species and so is also placed into this subgroup.

– ‘laconica’ subgroup. Species with incomplete set of s-setae (33/22224) and ms-setae (10/000) on body (as in Figs 55, 56). F. laconica sp. n., F. tertia sp. n., F. trisensilla sp. n. Other characters as in ‘macrochaetosa’ subgroup.

– ‘tatarica’ subgroup. The species are habitually specific due to slender body (Figs 69, 70), rather short macrosetae and short furca. They have complete set of s-setae (43/22235), ms of Abd.I present or absent. F. baida, F. calcarea sp. n., F. tatarica, F. torpeda, F. tubulata sp. n.

Folsomia inoculata holds a unique position in the group due to s-pattern on Abd.V, chaetotaxy of furca, and specific appearance (for details see Remarks for the species).

The state of knowledge of the group

We believe that representatives of the ‘inoculata’ group were previously collected and recorded by other researchers in the eastern areas of Asia. In the associated regional papers (Yosii 1939, 1977; Tanaka 1970, Lee 1973; Kurcheva 1977; Solntseva and Molodova 1979; Suma 1997; Yamauchi and Suma 1999; Furuno et al. 2000; Niijima and Hasegawa 2011; Hishi et al. 2012) they were possibly listed as either ‘F. fimetaria’, ‘F. cf. fimetaria’ or ‘Folsomia sp.’ Indeed, species of the ‘inoculata‘ group share several superficial characters with ‘fimetaria’ group members and so could be confused with them. If considering essential characters, PAO in the latter group is oval and short, thoracic Md macrosetae are absent, and abdominal tip often has foil setae.

Distribution and ecology

The known species of the group mostly inhabit the boreal zone of the Eastern Asia. If considering our unpublished materials from North America, one species (F. inoculata, together with its junior synonym F. ezoensis) has almost trans-Holarctic range. Subgroup of short-furcated species (‘tatarica’ sgr.) occupies areas close to the Ural Mts (excl. F. tubulata sp. n.) although does not penetrate to the main part of Europe. In North America (unpubl. material, coll. A. Fjellberg) the group is not so diverse and we have discovered only few, mostly new species. Representatives of the ‘inoculata’ group often predominate in litter of native forests and such ecological niche may be used as an additional difference from the ‘fimetaria’ group. The latter group prefers various disturbed habitats, organically enriched sites, etc. (F. candida, F. fimetaria, and F. litsteri, for example).

Key taxonomic characters of the group

Position of s-setae on tergites. The group show a high diversity of position of medial s-setae relatively to p-row – four patterns can be discriminated (Table 1). Three most frequent variants are shown in Figs 1–3.

Table 1.

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Position of medial s-setae on tergites in the ‘inoculata’ group.

Th.II–III	Abd.I–II	Abd.III	Species
in p-row	in p-row	in p-row	F. amurica sp. n., F. imparis sp. n., F. laconica sp. n., F. macrochaetosa, F. setifrontalis, F. tertia sp. n., F. trisensilla sp. n., F. baida, F. tubulata sp. n.
in front of p-row	in p-row	in p-row	F. bashkira, F. brevisensilla, F. hidakana, F. inoculata
in p-row	in p-row	in front of p-row	F. tatarica
in front of p-row	in front of p-row	in front of p-row	F. breviseta sp. n., F. calcarea sp. n., F. torpeda

S-pattern on Abd.IV and V. Position and differentiation of s-setae on Abd.V is one of the keys to understanding of evolution of the genus Folsomia (Potapov and Greenslade 2010). Most species of the ‘inoculata’ group show ‘4+1’ or weakly differentiated ‘3+1+1’ s-pattern widely distributed in the genus (Fig. 4). Three new species (F. laconica sp. n., F. tertia sp. n., and F. trisensilla sp. n.) loose two s-setae: lateral accp-s in dorsal pair of s-setae on Abd.IV and anterior as-s on Abd.V resulting in a pattern showing in Fig. 6. These three species also loose corner accp-s on Th.II and ms on Abd.I (Figs 55, 58, 65). These three s-setae loss (on Th.II, Abd.IV, and Abd.V) is a unique character for the genus: s-formula 33/22224 (instead of common for the genus 43/22235) was known neither in the ‘inoculata’ group nor in the genus, although similar but not identical reduction is typical of several species of the ‘sensibilis’ group (33/22225). In the latter case, as-s-setae of Abd.V remain in the set. Another trend is a differentiation of complete terminal set: s-setae of Abd.IV can undergo shortening (Fig. 5). Differentiation of Abd IV–V s-pattern is most marked in F. inoculata (Fig. 7).

Front setae on coxa of leg I. Species of the ‘tatarica’ subgroup, F. inoculata, F. brevisensilla, F. breviseta sp. n., and F. tertia sp. n. have two such setae, F. laconica sp. n., F. trisensilla sp. n., and species of the ‘macrochaetosa’ subgroup – three, and F. hidakana – four (Fig. 8). This trait probably reflects general number of setae on legs and furca while shows some exceptions.

Figures 1–8

. Folsomia spp. 1–3 Variants of position of medial s-setae on Th.III, Abd.I, and Abd.II 4–7 Sensillar patterns at the end of abdomen in F. amurica sp. n. (4), F. bashkira (5), F. laconica sp. n. (6), and F. inoculata (7) 8 Position and different number (two, three, and four) of frontal setae on coxa of leg I (encircled). Abbreviations: Md, Mdl, Ml–dorsal, dorso-lateral and lateral macroseta, m-accp, c-accp–medial and corner accp-s-setae, ms–ms-seta, as–as-s-seta, accp2, accp2 –accp-s-seta, upper sbcx, lower sbcx–upper and lower subcoxae, cx–coxa.

Setae on ventrum of metathorax. The species of the ‘inoculata’ group normally have three ventral setae on each side of Th.III, one of which is long and two are short (Fig. 9). Several species have fewer or more variable number of ventral thoracic setae or all these setae are subequal in size (F. inoculata, F. brevisensilla, and all species of the ‘tatarica’ subgroup). Two species sharply differ from other congeners of the group having no ventral setae on Th.III (F. breviseta sp. n., F. hidakana) (Fig. 10).

Characters of lower taxonomic value

– PAO in all ‘inoculata’ species is slender, with parallel edges, and more than 1.3 times longer than width of Ant.I (Figs 14, 24, 62, 78) that is probably a sharp characteristic of the group discriminating it from adjoining ‘fimetaria’ and ‘sensibilis’ groups. The so-called “inner denticles” along its edges and middle constriction are usually seen in all species in different extend while both characters considerably vary within populations.

– All species have three basal ms-setae on Ant.I: one ventral and two dorsal. Two dorsal bms-setae are arranged in a longitudinal line, proximal bms is longer (Figs 14, 23, 24). The proximal bms usually hardly differs from common setae and herewith should be carefully excluded if calculating common setae on Ant.I. Species of the ‘tatarica’ subgroup have proximal bms clearly shorter than common setae (Fig. 78) while its length also varies depending on specimens.

– The members of ‘hidakana’, ‘macrochaetosa’, and ‘laconica’ subgroups have minute subapical setae on posterior side of dens. The size of the seta varies depending on specimens and often hardly detectable. Small wrinkle in which this seta set in is always visible.

Figures 9–14.

Folsomia spp. 9–10 Ventrum of Th.II, Th.III, and Abd.I in F. imparis sp. n. (9), setae on Th.III present and F. hidakana (10), setae absent 11–12, 14 F. breviseta sp. n., furca, lateral view (11), appearance (12), PAO and Ant.I (14) 13 Appearance of F. hidakana. Abbreviation: vm–ventro-medial setae.

Descriptions of species

Subgroup ‘hidakana’

Folsomia breviseta Potapov & Kuznetsova, sp. n.

http://zoobank.org/62BCDE0A-6F11-4162-B7EA-58A0B2061542

Figs 11, 12, 14, 15–20

Type material

Holotype, female, Russia, NE Yakutia, Middle Indigirka, near Ust-Nera, 700 m alt., larch forest with thick lichen cover, litter, 22.vii.1992. Ten paratypes from the same biotope, five paratypes from mountain tundra (1500 m alt.) with bushes of Betula nana and one paratype from mosses in stony niche on northern slope (1600 m alt.) in the same location. All collected by N. Kuznetsova and M. Potapov. Deposited in MSPU.

Diagnosis

Blind. Dorsal macrosetae (Md) present on both Th.II and Th.III. Sensillary formula complete (43/22235; 10/100). Medial s-setae on body tergites short, set in anterior position. Macrosetae short. Ventral setae on Th.III absent. Anterior side of manubrium normally with 2+2 setae, dens with 18–22 anterior setae. Mucro bidentate.

Description

Body size from 1.0 (one adult male) to 1.7 mm. Body shape relatively tubular, general appearance not typical of ‘inoculata’ group due to short macrosetae (Fig. 12). Without ocelli and pigmentation. Cuticle with fine, hexagonal primary granulation (“smooth”). PAO slender and long, middle constriction varies, ‘inner denticles’ usually well developed, PAO length 1.8–1.9 as long as width of Ant.I and 2.3–2.5 as long as inner unguis length (Fig. 14). Labium complete, guard setae e7 present, three proximal and four basomedian setae. Ventral side of head with 4+4 postlabial setae. Ant.I with 13–15 common setae, two ventral s-setae (s) and three basal micro s-setae (bms): two dorsal bms (short and long) and one ventral bms. Ant.II with three bms and one latero-distal s, Ant.III with one bms and four distal s (lateral s absent, Fig. 15). Several tubular s-setae on Ant.IV. Organite small.

Common setae short. Sensillary formula as 43/22235 (s) and 10/100 (ms). S-setae short, four s-setae on dorsal side of Abd.V longer. Medial s-setae on Th.II–Abd.III situated in front position, on Abd.I–III between Md and Mdl (Figs 16, 17). Abd.V with five s-setae arranged as three in dorsal position, thin, as long as common setae (as, accp1, accp2), one lateral, thicker than dorsal, and one latero-ventral, short (‘3+1+1’ pattern) (Fig. 18), accp3 s-setae subequal to accp2. Macrosetae smooth and short, 2,2/3,3,3 in number, medial ones on Abd.V much shorter than dens (2.3–3.1) and 1.8–2.3 times longer than mucro (Fig. 18). Axial chaetotaxy as 10–12,7–8,/5–6,5,5. Thorax without ventral setae.

Empodial appendage as long as 0.5–0.6 unguis. Tibiotarsi with 24–27 setae on legs I–II, and 28–32 on leg III. Upper and lower subcoxae of legs I–III with 0,1/3,6–8/5–7,7–9 setae, respectively. Coxae of leg I with two front setae. Ventral tube with 4+4 latero-distal and 5–7 posterior setae (two in distal transversal row and 3–5 in more proximal position), anteriorly without setae. Tenaculum with 4+4 teeth and a seta. Anterior furcal subcoxae with 12–15, posterior one with six setae. Anterior side of manubrium normally with 2+2 setae at distal edge, arranged in two longitudinal lines (Fig. 19). One additional seta often present on one side in a distance from main group resulting in 2+3 set (Fig. 11). One of the paratypes shows 2+1 anterior setae on manubrium (Fig. 20). Posterior side of manubrium with 4+4 latero-basal, two apical setae (ap), 2+2 setae in distal transversal row (M1, L1), two pairs of lateral setae, and 5–6+5–6 in central part (Fig. 11). Dens with 18–22 anterior setae. Posterior side of dens crenulated and with seven setae: four basal, two at the middle, and one (not especially small) at base of mucro (Fig. 11). Mucro bidentate. Ratio of manubrium : dens : mucro = 4.1–4.5 : 5.1–5.8 : 1. Males present.

Figures 15–20.

F. breviseta sp. n. 15Ant.III (area of common position of lateral s-setae marked) 16–17 Position of macrosetae, setae of p-row, and s-setae on posterior (16) and anterior (17) half of corpus 18 Chaetotaxy of Abd. IV–VI 19–20 Chaetotaxy of anterior side of manubrium, variations. bms–basal ms.

Remarks

Folsomia breviseta sp. n. combines several characters rare for the group: short macrosetae and s-setae, anterior position of medial s-setae on body tergites, the absence of ventral setae on Th.III. A loss of lateral s-setae on Ant.III is a very peculiar character while the nature of this character is not easy to interpret since all species of the family Isotomidae, if not all Collembola, have these s-setae. The absence of s-setae was confirmed in all available specimens. Beyond ‘inoculata’ group several blind species with two pairs of setae on manubrium can be confused with F. breviseta sp. n., for example, F. bisetosa Gisin, F. cephalota Bu et al., and F. sensibilis Kseneman. All these species belong to other groups and therefore differ essentially by characters of high rank.

Distribution and ecology

The species is known only from the type locality where it inhabits mountain forests and tundra.

Derivatio nominis

The new species name reflects short setae on body.

Folsomia hidakana Uchida & Tamura, 1968

Figs 10, 13, 21–27, 28, 90

Material

Japan, Honshu Island, Nobeyama, Nagano, 10.x.2012, coll. M. Hasegawa; Kitaibaraki, 2.xi.2011, coll. M. Hasegawa; Hokkaido Island. Shore of Harutori Lake, Kushiro city, 14.v.2014 and 19.viii.2014, coll. Y. Suma; Shiretoko Peninsula, surroundings of Utoro, litter of mixed forest, 90 m alt., 20.viii.2016, 44.1006°N, 145.0584°E, coll. M. Potapov and N. Kuznetsova; Shiretoko Peninsula, trail to Rausu Mount, ~200 m alt., 29.ix.2013, coll. R. Kitagawa and S. Fujii; ibidem, trail to Rausu Mount, ~1000 m alt, oak litter, coll. M. Potapov and N. Kuznetsova.

North Korea. Hamgyong-namdo Province (= South Hamgyong), valley N from Song-riong, 03.vi.1987, and SW from Tanchon, 30.v.1987, coll. A. Szeptycki.

Far East of Russia, Primorsky Krai, Lazovsky District, nearby Preobrazheniye, litter and rotten wood in deciduous and coniferous forests, 400–700 m alt., 21.ix.2011, coll. M. Potapov, Y. Bu, H. Chen-Wang; Khasansky District, Peschany Peninsula, near Beregovoye, litter under dogrose, 09.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos, Khasansky District, ~15 km S Kraskino, Mramorny Cape, oak wood litter and soil under coastal reed, 28.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; Khasansky District, ~15 km W Kraskino, Mayachnoye (Chertova Gorka), forest litter, 28.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; Khasansky District, Krabbe Peninsula, Astafyeva Cape, deciduous litter, v.2007, coll. E. Sokolova; Khasansky District, “Kedrovaya Pad”, mixed forest, litter, 29.vii.2016, coll. M. Potapov and N. Kuznetsova; ibidem, coniferous and deciduos litter, 29.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; ibidem, 03.x.2009, coll. O. Smirnova, ibidem, v.2015, coll. A. Matalin; Khasansky District, near Barabash, oak wood on slope, litter, 27.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; Partizansky District, vicinities of Ekaterinovka, Chondalaz (= Lazovy) Range, oak litter, 26.ix.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; Ussuriyski District, Ussuriyski Reserve, decaying wood, 5.x.2004, coll. M. Potapov, L. Deharveng, R. Pomorski, and A. Bedos; Shkotovsky District, Khualaza Mount, 2.x.2004, coll. R. Pomorski; between Vladivostok and Artem, botanical garden, litter of mixed forest, ix.2012 and 04.x.2009, coll. O. Smirnova; Terneysky District, Sikhote-Alimski Reserve, Kabany station, forest litter, 08.viii.2017, coll. N. Kuznetsova, A. Geras’kina, A. Kuprin; Kavalerovski District, road Kavalerovo-Dal’negorsk, 44.3844°N, 135.3639°E, mossy larch forest with Rhododendron, 09.viii.2017, coll. N. Kuznetsova, A. Geras’kina, A. Kuprin; Khabarovsky Krai, Vaninsky District, nearby Datta, coastal larch-wood, 28.ix.2011, coll. M. Potapov; Vaninsky District, five km N Vysokogorny, valley of Mulinka River, larch-forest litter, ~ 600 m alt., 29.ix.2011, coll. M. Potapov.

Description

Body size from 1.2 to 1.7 mm. Body shape as common for the group, not slender (Fig. 13). Usually with large pigment grains rarely scattered on body, more on fused Abd.IV–VI. Cuticle with fine hexagonal primary granulation (“smooth”). Ocelli absent. PAO slender, with clear middle constriction, ‘inner denticles’ hardly developed, its length 1.2–1.7 as long as width of Ant.I and 1.6–2.0 as long as inner unguis length (Fig. 24). Labium complete, guard setae e7 present, three proximal and four basomedian setae. Ventral side of head with 4+4 postlabial setae. Ant.I with 15–17 common setae, 2–3 (see the discussion below, Figs 23, 24) ventral s-setae (s) and three basal micro s-setae (bms): two dorsal bms (short and long) and one ventral bms. Ant.II with three bms and one latero-distal s, Ant.III with one bms and with 5–6 distal s (one or two lateral s, Fig. 25). Organite varies in shape, often large.

Figures 21–27.

F. hidakana 21–22 Position of macrosetae, setae of p-row, and s-setae on anterior (21) and posterior (22) half of corpus 23Ant.I (S Primorye: Far East of Russia) 24PAO and Ant.I (Honshu: Japan) 25Ant.III 26–27 Manubrium, anterior (26) and posterior (27) views. Abbreviations: bms–basal ms, ls–lateral s.

Common setae middle-sized. Setae covering polychaetotic: Abd.IV with 7–9 p-setae between medial accp-s, Abd.V with m1-setae (marked on Fig. 28). Sensillary formula as 43/22235 (s) and 10/100 (ms). S-setae long and thin, as long as common setae. Medial s-setae on Th.II–III situated in front position, nearby Md macrosetae, on Abd.I–III in p-row, between Md and Mdl (Figs 21, 22). Abd.V with five s-setae arranged as four in dorsal position, rather long (as, accp1, accp2, accp3), and one latero-ventral, middle-sized (weakly differentiated ‘4+1’ pattern), accp3 s-setae insignificantly shorter and thicker than accp2 (Fig. 28). Macrosetae smooth, their length vary from long to moderately long, 2,2/3,3,3 in number, medial ones on Abd.V a little shorter than dens (1.0–1.3) and 3.7–6.0 times longer than mucro. Axial chaetotaxy as 9–12,7–9,/4–5,4–5,4. Thorax without ventral setae (Fig. 10).

Empodial appendage approximately half as long as unguis. All tibiotarsi with many additional setae: 29–33 on legs I–II, ~38–42 on leg III. Upper and lower subcoxae of legs I–III with 0,1/4–6,8–11/8–12,8–11 setae, respectively. Coxae of leg I with four (rarely five) front setae. Ventral tube with 5–6+5–6 latero-distal and 6–8 posterior setae, anteriorly without setae. Tenaculum with 4+4 teeth and a seta. Anterior furcal subcoxae with 11–14, posterior one with four setae. Anterior side of manubrium with 4–6+4–6 pair setae and usually with two unpaired axial setae (Fig. 26). Posterior side of manubrium with 3+3 latero-basal, two apical setae (ap), 2+2 setae in distal transversal row (M1, L1), one pair of lateral setae, and 4(3)+4(3) in central part (Fig. 27). Dens with 19–23 anterior setae. Posterior side of dens crenulated and with six setae: three basal, two at the middle, and one rudimentary at base of mucro (often hardly visible). Mucro bidentate. Ratio of manubrium : dens : mucro = 3.7–6.2 : 4.5–7.0 : 1. Males present.

Remarks

Our specimens fit to the original description of F. hidakana in all significant features. Uchida and Tamura (1968) did not show in figures a subapical rudimentary seta on posterior side of dens and short latero-central setae (l2) on manubrium (probably overlooked). We also found wider variability in most characters that is certainly explained by larger material we have studied. Macrosetae on figures in first description (Figs 28, 35 in Uchida and Tamura 1968) seem to be shorter than in our material. Folsomia hidakana is a peculiar species due to anterior position of medial s-setae on thoracic segments, 5+5 or more latero-distal setae on ventral tube (vs 4+4 that is more common for the group), four setae on posterior furcal subcoxa (fewer than common for the group), 3+3 latero-basal and 1+1 latero-central setae on posterior side of manubrium (fewer than common for the group). The absence of ventral setae on Th.III is the main differentiated feature of F. hidakana shared only with allopatric F. breviseta, the two species are combined in the formal subgroup ‘hidakana’ by us. From ‘macrochaetosa’ group F. hidakana differ by more setae on body and more lateral position of accp1-s on Abd.V (see Fig. 28 vs Figs 29, 32). Being often mixed with habitually similar species (often with F. imparis sp. n.), F. hidakana is normally easy to recognize by scattered pigment grains on body.

Figures 28–35.

Folsomia spp. 28 F. hidakana, end of abdomen, dorsal view 29–31 F. amurica sp. n., end of abdomen, specimens from Amurskaya Region, dorsal (29) and lateral views (31), specimen from Inner Mongolia Province, lateral view (30) 32 F. imparis sp. n., end of abdomen 33–35 F. amurica sp. n., chaetotaxy of anterior side of manubrium, variations.

Specimens collected in Japan, both in Honshu and Hokkaido, differ from specimens from Russia by three (vs two) s-setae on Ant.I. In Japanese populations the individuals with two s rarely occur so we keep both variants within diagnosis of F. hidakana.

Distribution and ecology

Species was described from Hokkaido (Hidaka-Mombetsu) and subsequently listed in catalogues of Japanese Collembola (Yosii 1977; Furuno et al. 2000; Niijima and Hasegawa 2011). Known from Hokkaido (Suma 1997, 2008, Hishi et al. 2012), eastern Honshu (Ibaraki) (Hasegawa et al. 2009), Aomori Pref. (Yamauchi and Suma 1999, 2009). In Far East of Russia the species was previously recorded near Ussuriysk (Kutyreva 1988) and in Shikotan Island (as ‘F. sp.aff. hidakana’ in Potapov and Marusik 2000).

As a whole, distributional range of the species appears to cover southern area of the Russian Far East, North Korea, and northern half of Japan (Fig. 90). It inhabits forest litter and decaying wood in low mountains, rare in higher altitudes.

Subgroup ‘macrochaetosa’