Appendisotoma stebayevae ( Grinbergs, 1962 )

Potapov, Mikhail, Babenko, Anatoly, Bu, Yun, Bayartogtokh, Badamdorj, Gulgenova, Ayuna & Luan, Yun-Xia, 2024, Taxonomy of the Cryptopygus complex. IV. Cyclomorphosis in three species of Appendisotoma and description of a new species from Kazakhstan (Collembola, Isotomidae), Zootaxa 5453 (4), pp. 487-510 : 493-498

Appendisotoma stebayevae ( Grinbergs, 1962)

Figs 16–34 , 62

Syn.: Proisotoma asiatica Martynova, 1971 (also as Appendisotoma )

Syn.?: Proisotoma xinjiangica Hao & Huang, 1995 (also as Appendisotoma )

Syn.nov.: Appendisotoma juliannae Traser et al., 1993

Syn.nov.: Proisotoma franzi Haybach, 1962 (also as Appendisotoma )

Syn.nov.: Appendisotoma montana Martynova, 1969

Material. Winter form: Russia, European part, S Moscow area, Malinki station , on surface of stream among melting snow, edge: mixed forest—damp meadow. 08.04.2001, leg. M.P .

W Moscow area, nearby Shakhovskaya, mixed forest, rotten wood, 08.04.2024, leg. M.P.

N Moscow area, Odintsovsky district, Zvenigorod station of MSU, pitfall traps in snow, in mixed forest, near stream. 23– 30.01.2023, leg. A. Shamrina and P. Petrov.

Russia, Central Yakutia , Leno-Vilyuysky interfluve, Gorny ulus, nearby Asym, N 62 24'01'' E 126 47'35'': larch forest, 18.08.2022, leg. A. Burnasheva. One other site nearby, leg. A. Burnasheva (in mixture with summer form)

Russia, Far East, Khabarovsk, Krasnoflotsky district , mossy burnt site, May 2007, leg. E. Sokolova.

Kyrgyzstan, Tien Shan , Terskey Alatau, fir forest, 2600 m alt., 19.03.1968. leg. P. Vtorov (holotype of Appendisotoma montanum Martynova, 1969 ) .

Hungary, Asotthalom , 04.01.1988. leg. G. Traser (2 paratypes of Appendisotoma juliannae ) .

Summer form: Russia (European part), Samara Region, Bol’shechernigovski District, Kirillov Dol, 4 km SW from Fitali , ~ N 52o 03’ E 51o 20’, July 1993, slope steppe, leg. I. Smelyanski.

Volgograd Region, Pallasovski District, Elton Lake, (mouth of Khara River), steppe in depression (under Amygdalus nana ), 19.04.2007, leg. M.P.

Russia (Asiatic part), Tuva: Mugur-Aksy Mt., upper part, dry tundra ( Oxytropis sp. ), 22.07.1993, leg. S.S.; Tere-Khol’ Lake, poplar oasis, 04.08.1985, leg. I.Vtorov. Tere-Khol’ Lake, sands on lake shore with Caragana bungei , 13.07.1993, leg. S.S. 10 km NW from Erzin, Tsyger-Els, steppe ( Caragana bungei ), 12.07.1993, leg. S.S. Valley of Aryskanyg-Hem River, under Caragana spinosa , 15.07.1993, leg. S.S. ~2 км from Samagaltai, poplar wood in floodplain, 15.07.1993, leg. S.S., Shivilig-Hem, fir forest, ant nest, 25.07.1978, leg. S.S.

Zabaikalsky Krai, Onon District, Chindant, meadow, leg. S.S.; Zabaikalsky Krai, Alkhanai, valley of Ilya River, Ara-Ilya, N 50º55.865' E 113º12.393', 876 m alt., sedge-herb meadow, 12.07.2014, leg. A. Gulgenova.

Yakutia: Central Yakutia, Leno-Vilyuysky interfluve, Gorny ulus, nearby Asym N 62 23'56'' E 126 48'18'': larch forest, 28.06.2022, leg. A. Burnasheva. One other site nearby, leg. A. Burnasheva; Central Yakutia, Leno-Vilyuysky interfluve, Gorny ulus, nearby Asym N 62 24'01'' E 126 47'35'': burnt larch forest, 18.08.2022, leg. A. Burnasheva. Another site nearby, leg. A. Burnasheva (in mixture with winter form); Central Yakutia, 17 km from Yakutsk to Tabaga, valley of Lena river, birch-wood, litter, 14.07.1992, leg. M.P.; Northern Yakutia, Verkhoyanskyi range, Orto-Salakh river (near Kele), Populus and Chosenia rotten wood, 23.07.1989, leg.G.Lukovtsev.

Buryat Republic: Baikal Lake shore, ~ 30 km N Severobaikalsk, near Slyudyanskoye Lake , swampy larch wood, N 55.482, E 109.166, ~ 400 m alt., under bark of tree, 17.08.2013, leg. M.P., A. Gulgenova. Vitim plateau (E Buryatia), Eravninskaya Basin, flotation of sand on NW shore of bank of Bol'shaya Eravna Lake , 7.06.2009, leg. A. Gulgenova. Schuch'ye Lake , under Spiraea aquilegifolia , in pit-fall traps, 14.06.2013, 14.06.2013, leg. A. Gulgenova. Selenga River mouth, steppe, 18.08.1982, leg. S.S .

W Siberia: Kemerovo Region, Novonikolayevka, steppe, 15.07.1984, leg. S.S. Khakassia, Maina (~45 rm from Askiz), steppe, 16.07.1990, leg. S.S .

Mongolia: Zavkhan Aimag, Tosontsengel Soum, 15 km NW from Tosontsengel , larch forest, soil, 2031 m., N 48.816667 E 98.103056, 22.07.2004., leg. B.Bayartogtokh ; Khovd Aimag, Erdenebüren Soum , soil of mountain steppe (under Caragana sp. ), N 49.320833 E 91.310556,Alt. 1470 m, 01.08.2004, leg. B.Bayartogtokh ; Uvurkhangai Aimag, Arvaikheer Soum, 6 km NE from Arvaikheer , soils of mountain steppe, N 46.301389 E 102.777778, Alt. 1860 m, 07.08.2004, leg. B.Bayartogtokh.

Kazakhstan: Aksu-Dzabagly Reserve, Dzabagly-Tau Range, 2200 alt., S slope, terrace, ephemeral meadow, 02.05.1991, leg. S. Iordansky; Aksu-Dzabagly Reserve, Kshi-Kaindy Canion (upper part), lower subalpine, 2500 alt. alt., 28.07.90, ibidem, Kshi-Kaindy Pass, 300 m alt., xerophytic steppe, leg. S. Iordansky; Aksu-Dzabagly Reserve, N slope, Ugamsky Range, Aksu river, under Betula sp. , 2250 alt., 17.06.1995, leg. A. Matalin; Abai Region, Irtysh River, Semiyarka, pine wood, 26.07.1972, leg. S.S.

China: W China, Inner Mongolia Province (area close to Ningxia Pr.), Helan Mts., near Halawu , N 38.86675 E 105.910183, 2325 m alt., 11.08.2010, leg. C.W. Huang, Y. Bu.

Materials of Appendisotoma sp. aff. stebayevae : Central China, S Gansu Province, Aut.reg. Gannan, near Xiahe (=Labrang) (close to border to Qianchai), ~ 3000 m alt., soil in glade in spruce forest, 21.08.2014, leg. S. Dmitriev.

Description. Body size 0.7–1.0 mm. Corpus slender. Pale, from fully unpigmented to spotty bluish-grey (partly affected by cyclomorphosis). Abd.V separated from Abd.IV and fused with Abd.VI. Cuticle with thin hexagonal primary granulation. Ocelli 8+8 ( Figs 18 , 26, 31, 33 ), G and H always smaller, one or both often hardly visible. Eye pigmentation can mask real number and size of ocelli ( Fig. 16, 17 ). Ratio PAO length: ocellus = 1.5–3.2 (affected by cyclomorphosis), 0.4–0.7 as long as width of Ant.I. PAO shorter than inner unguis length (0.7–1.0). Maxillary head with unmodified lamellae. Maxillary outer lobe with 4 sublobal hairs, maxillary palp simple. Labral formula as 4/5,5,4. Labium with 5 usual papillae (А–Е) and labial formula A1B4C0D4E6 (15 guards at whole), guard chaetae e7 absent, 3 proximal, 4 basomedian and 5 basolateral chaetae. Ventral side of head with 4+4 (rarely 5+5) chaetae. Ant.I with 16 common chaetae (11 of basal set and 5 additional ones), 2 s-chaetae and 3 bms-chaetae, 2 dorsal and 1 ventral. 2 dorsal bms on Ant.I large, chaetae-like. Ant.II with 1 latero-distal s and 5 bms (2 dorsal set together, 2 ventral and 1 additional) ( Fig. 22 ). Ant.III with 1 bms, 6 distal s of AO (including 2 lateral s), and with 3–6 additional s-chaetae ( Fig. 22 ). S-chaetae on Ant.IV weakly differentiated. Organite small, micro s-chaeta small, of common shape. Males with spurs on Ant.II and III.

Common chaetae smooth. S-formula as 3,3/2,2,2,4,4 (s), 1,0/0,0,0 (ms) ( Figs 19, 20 ). Macrochaetae 1(2),1(2)/3,3,3 in number, medial macrochaetae on Th.II–Abd.II much shorter and often hardly visible (not shown in Fig. 19 ). Macrochaetae on Abd.V 1.2–1.8 times longer than dens and 2.1–4.3 times longer than mucro. Foil chaetae at the tip of abdomen absent. Axial chaetotaxy of Th.II–Abd.III as 7–9,6–7/4(5),4(5),4–5,5–7. Thoracic segments without ventral chaetae.

Unguis with lateral teeth and one variable inner tooth (sometimes absent) ( Fig. 21 ). Empodial appendage 0.5–0.7 as long as unguis. Tibiotarsi without T-chaetae (at whole with 7 chaetae in apical whorl). Tibiotarsi I and II usually with 1–2 additional chaetae (21+1–2 = 22–23 chaetae at whole), tibiotarsi III with few (>4) additional chaetae. Adult males without differentiated spurs on Leg III. Tibiotarsal tenent hairs pointed or with blunt tips, 0.6–1.2 as long as length of inner edge of unguis (affected by cyclomorphosis). Ventral tube with 4+4 laterodistal and usually 5 posterior chaetae (2 in distal transversal row and 3 proximal), anteriorly without chaetae. Tenaculum with 4+4 or 3+3 (affected by cyclomorphosis) teeth and 2 chaetae. Anterior furcal subcoxa with 12–18, posterior one with 8–9 chaetae. Anterior side of manubrium with 2+2, 1+1, 1+1 chaetae ( Fig. 34 ), posterior side with 3+3 laterobasal and many chaetae on main part, normally with 2+2 latero-central chaetae. Dens crenulate or with notches on posterior side (affected by cyclomorphosis), with 4 (very rarely 3 on one side) anterior chaetae. Posterior side with 5 chaetae. External lobe near apex of dens present or absent (cyclomorphosis). Mucro with 4–5 teeth: 3 ones positioned in a line (apical, subapical and proximal), one outer and one inner. Inner tooth often absent, its size and position vary ( Figs 28, 29 ). Ratio manubrium: dens: mucro = 3.2–4.4: 1.8–2.4: 1.

Males present, without any specific modification in reproductive stage.

Cyclomorphosis. "Winter" specimens have notches and apical lobe on dens variable in size ( Figs 28, 29 vs. 24), more developed cornea of ocelli ( Figs 31, 33 vs. 26), chitinized furcal apparatus ( Fig. 34 ), and 3+3 (vs.4+4) teeth on tenaculum ( Fig. 30 vs. 25). Tibiotarsal tenent hairs longer in "winter" specimens: ratio Tibia t.h.: inner edge of U = 0.8–1.2(W) vs. 0.6–0.8(S). "Winter" form is usually darker but the variability within the "summer" form is high and masks the colour difference between the forms. Eye spot appears to have similar coloration in the two forms in spite of difference in size of ocelli.

Winter form may be present even in May (see the Materials and Methods part). In population from central Yakutia both winter and summer forms are mixed together in August (18.08.2022). The occurrence of both forms in one locality was also recorded by Traser et al. (1993, 2002) and Traser & Horváth-Szováti (2006) (as A. juliannae and P. franzi ) and Martynova & Sklyar (1973) (as A. montana and P. franzi ). After Traser & Horváth-Szováti (2006), both two "species" occurred at spring time (March 26–27) in Csévharaszt ( Hungary). Martynova & Sklyar (1973) tagged A. montana as strictly autumn-winter in the nests of small mammals in the Azov steppes. We guess, the lifetime of the two seasonal forms and their overlap throughout the year depends on climate, but further study is needed to verify this.

Remarks. Appendisotoma stebayevae is a well-defined species due to characteristic pigmentation (unpigmented or, more rarely, pale greyish-blue body with black eye spots), furca, and incomplete apical whorl of tibiotarsi (7 chaetae). The latter character is shared with only A. monomorpha sp. nov., which has more reduced furca.

Specimens from Gansu Province (Central China, see the Material’s part) belong to another species with 1+1 chaetae on ventral side of Th.III (absent in A. stebayevae ), and 6 (vs.5) additional chaetae on Ant.I. The incomplete description of Proisotoma xinjiangica from Xinjiang (Western China) does not allow us to describe a new species based on Gansu specimens.

Synonyms. In the Palaearctic key for the genus ( Potapov 2001), three species of Appendisotoma share the same chaetotaxy on anterior side of manubrium as in A. stebayevae (i.e. 2+2, 1+1, 1+1 chaetae, as in Fig. 34 ). They are discriminated based on presence of apical lobe on dens, 3+3/4+4 teeth on retinaculum, and pigmentation of the body. After our study of vast material from different parts of the Palearctic we concluded that the "differential" characters mentioned above are affected by season and reflect the morphological differences between summer and winter forms only.

Appendisotoma juliannae ( Hungary) and A. montana ( Kazakhstan), described from winter collections with dates 04.01.1988 and 19.03.1968, respectively, have lobe on dens. Therefore, we conclude that they belong to a winter form of A. stebayevae . Their coloration, pale grey-blue in the former species and pale violet in the latter, also indicate the usual winter darkening of A. stebayevae , which is normally colorless. After our examination of type specimens of A. montana and A. juliannae , all other characters (e.g. distribution of s-chaetae, tibiotarsal chaetotaxy) appear to be identical with A. stebayevae . In A. juliannae we observed 4+4 s-chaetae on Abd.V (vs. 2+ 2 in original description). We have not seen the type specimens of Proisotoma franzi from Austria but its synonymy to our widely distributed species appears certain. Proisotoma franzi and P. asiatica both fit to a summer form of A. stebayevae .

According to the catalogues by Kaprus’ et al. (2006) and Dányi & Traser (2008), both A. franzi and A. montana were recorded in Ukraine and Hungary, indicating the presence of both both summer and winter forms of A. stebayevae . It is telling that both "species" were found at the same location for both countries mentioned. The species was recorded as A. franzi in Poland ( Sterzyńska et al. 2007) and Austria ( Querner 2008).

Both P. stebayevae and P. franzi were described in 1962. Priority of the former name upon the latter follows the earlier publication of Grinbergs (1962).

Distribution and ecology. We suppose a Palaearctic distribution of the species, if accepting all its synonyms ( Fig. 62 ). The species is sparsely recorded in European part of the region. In arid areas of Asia it is a frequent species in steppes and dry forests. So far S. stebayevae has not been observed on snow (apart two records near Moscow).

Figures

FIGURE 34. Furca in Appendisotoma stebayevae, winter form, anterior view (Yakutia), basal condyle less visible and not shown. Abbreviations: BR—basal rod; BP2—basal plate 2; BS2, BS3—basal sclerite 2 and 3.

FIGURES 16–22. Appendisotoma stebayevae, summer form: 16, 17, pigmentation of eye spot in individual from Kazakhstan (16) and Central China (17); 18, ocelli and PAO; 19, 20, macrochaetae and s-chaetae on thorax (19) and abdomen (20); 21, tibiotarsus III, lateral view; 22, Ant.I–III, dorsal view of right antenna. Abbreviations: as—additional s-chaetae, ls, ls’—lateral s-chaetae of AO, other abbreviations as on Figs 1–7.

FIGURES 23–33. Cyclomorphosis in Appendisotoma stebayevae, summer (23–26) and winter (27–33) forms: 23, 27, habitus of subadult individuals; 32, habitus of juvenile individual; 24, 28, 29, furca, lateral view (posterior side of manubrium not shown); 25, 30, retinaculum; 26, 31, 33 ocelli and PAO. Abbreviations: e.l.—external lobe on dens.

FIGURES 62–64. Records of A. stebayevae (62), A. bisetosa (63), A. monomorpha sp. nov. (63), and A. sibirica (64). The records blocking previous ones are not shown and not referred (especially in Tuva). Open circles—literature records (Dunger 1982; Grinbergs 1962; Hao & Huang 1995; Haybach 1961; Martynova 1971; Martynova & Sklyar 1973; Potapov et al. 2020; Sławska 2000; Smolis & Skarżyński 2003; Stebaeva 1974; Traser et al. 1993). The records in Siberia are given in more detail by Stebaeva (1976). Abbreviations: type—type locality, A.a., A.f., A.j., A.m., A.x.—type localities of A. asiatica, A. franzi, A. juliannae, A. montana, A. xinjiangica, respectively.