Parisotoma baicalica Potapov & Gulgenova, 2020

Potapov, Mikhail, Huang, Cheng-Wang, Gulgenova, Ayuna & Luan, Yun-Xia, 2020, New and little known Isotomidae (Collembola) from the shore of Lake Baikal and saline lakes of continental Asia, ZooKeys 935, pp. 1-24 : 1

Parisotoma baicalica Potapov & Gulgenova sp. nov. Figures 43 , 44-57

Type material.

Holotype: female. Russia, East Siberia, Irkutskaya Region, Slyudyanka District, Angasolskaya, shore of Lake Baikal, 51.7314°N, 103.8280°E, in shingle, 09.VIII.2015, coll. G. Efanov (deposited in MSPU). 3 paratypes from the same place (deposited in MSPU), 4 paratypes from Russia, Buryat Republic, Barguzinskiy District, 53.29645°N, 108.6213°E, floatation of shingle at water edge, 03.VIII.2014, coll. M. Potapov and A. Gulgenova (2 paratypes deposited in SMNG, 2 - in BSU).

Description.

Body length from 0,7 to 0,9 mm. Pale with diffuse greyish pigment on body, eye spot less marked than in most species of Parisotoma with one ocellus (Fig. 43 ). Ant.1 with 5-7 short s-setae ventro-laterally, three basal microsetae, two dorsal and one ventral (Fig. 47 ). Inner s-setae of AO III large. Ant.4 as common for the genus. One small ocellus on each side of head (Fig. 46 ). PAO wide, 1.4-1.8 as long as internal crest of Claw 3. Labral formula 4/554, apical folds sharp, as in P. notabilis ( Schäffer, 1896). Maxillary outer lobe with four sublobal hairs and trifurcate apical palp. Labial palp with five papillae (A-E) and full set of guards (16, including e7), lateral process expanded. Papilla B with small basal process on its inner side (Fig. 52 ) (see the remarks). Labium with five basomedian, five basolateral, and four proximal setae. Number of postlabial setae from 3+3 to 4+4 (Figs 48 and 49 ), in the latter case an additional pair set between a1 and m1 (marked in Fig. 48 ). Inner mouthparts as usual for the genus: lamella 1 longer than capitulum with apex fan-shaped expanded, with marginal ciliation and one row of long denticles on inner side, lamella 6 with marginal ciliation and several (>3) irregular rows of denticles. Lower subcoxa of Leg 1 with one outer seta (Fig. 44 ). Tibiotarsi of all legs with only seven setae in apical whorl. Claw slender, without clear teeth (Fig. 55 ). Empodial appendage with broad lamella. Ventral tube with 3+3 lateral, 3+3 anterior (rarely two or four), and 4-6 posterior setae (Fig. 54 ). Retinaculum with 4+4 teeth and 2(3) setae. Furcal subcoxa with 27-35 setae. Manubrial thickening simple. Anterior side of manubrium with numerous setae of which 2+2 shorter medial ones in its apical part. Dens with numerous setae on anterior side and eight setae on posterior side (two basal, three internal and three external) (Fig. 56 ). Mucro with three teeth (Fig. 53 ).

Macrosetae differentiated, on last abdominal segments with few cilia (Fig. 45 ), on Abd.V shorter than length of tergite (ca. 0.6). S-setae thin, well different from common setae, pattern of s-setae complete, s-formula Th.II-Abd.V: 2al+6accp, 1al+6accp / 6 accp, 6 accp, 6accp, 1 am+6 accp, 2 am + 5 accp (Fig. 44 ). Micro s-setae 1,1/1,1,1 (ms) on Th.II-Abd.III. Micro s-setae of Abd.III shorter than s-setae (Fig. 10 ). As a rule, two common setae of p-row separate neighbouring accp s-setae. Formula of common setae in p-row between s and ms: 3-4s1-2s2s1s (Abd.I), 3-5s1-2s2s2-3s1-2s1-2s (Abd.II), 3-5s1-3s2-4s2-4s1-2ms0s1-2s (Abd.III), 1-3s2-3s2s1-2s2-4(s)1s (Abd.IV) (Fig. 44 ). Males present.

Affinity.

Due to posterior position of accp4 s-setae on Abd.IV the species, as expected, belongs to Palearctic branch of species of the genus Parisotoma ( Potapov et al. 2011). Short macrosetae, many s on Ant.1, and increased number of common setae between s-setae in p-row indicate the similarity to P. appressopilosa Potapov, 1991, described also from Baikal shore. They differ in number of laterodistal setae on ventral tube (3+3 in P. baicalica sp. nov. vs. 2+2 in P. appressopilosa ), outer setae on lower subcoxa of Leg 1 (one vs. two), shape of claw (more slender in P. baicalica sp. nov.), number of s-setae on body tergites (fewer in P. appressopilosa ) and number of internal setae (three vs. two) on dens. In appearance, the grey P. baicalica sp. nov. is well distinguished from the white P. appressopilosa if mixed in one site. The new species occurs along Baikal shore where the third congener, P. reducta Rusek, 1984, is very common in the forest litter. Both species are grey and can be mixed together in littoral zone. Less distinct eye pigment and shorter macrosetae readily help to discriminate between them. They also differ in size of lateral process of papilla E (Fig. 50 vs. Fig. 51 ), number of internal setae on dens (Fig. 56 vs. Fig. 57 ), outer setae on lower subcoxa of Leg 1 and other characters. P. terricola Rusek, 1984 (also described from Baikal) and P. baicalica sp. nov. share large inner s-setae of AO on Ant.3. Concerning European species, P. agrelli (Delamare Deboutteville, 1950) lives on sea shores and most resembles the new species due to short macrosetae, small ommatidia, and 3+3 laterodistal setae on ventral tube. They sharply differ in outer setae on lower subcoxa of Leg 1 (absent in P. baicalica sp. nov.) and number of s on Ant.1 (only two in P. agrelli ).

Slender claw, polychaetosis, short macrosetae, and expanded lateral process of papilla E indicate adaptation to live in contact to fresh water. The combination of 3+3 laterodistal setae on ventral tube and only one outer seta on lower subcoxa of Leg 1 indicate the formal similarity with the eurytopic species P. notabilis (rare at Lake Baikal) but P. baicalica sp. nov. differs by all “littoral” characters mentioned above.

The value of basal process on labial papilla B (Fig. 52 ) calls for further study. So far it was not mentioned in the descriptions of labium while we have seen it also in P. reducta and P. appressopilosa that may suggest its diagnostic importance for the genus Parisotoma .

Distribution and ecology.

Known only from two distant localities on the Baikal shore. A littoral species.

Name derivation.

It is named after the location of the type locality.

New species records on the shore of Lake Baikal

Folsomia uniramia Potapov & Gulgenova, 2013: Buryat Republic, SE shore of Lake Baikal, at Ust’ -Barguzin, 53.4086°N, 108.9879°E, floatation of sand at 5 m distance from water edge, 05.VIII.2014, coll. M. Potapov and A. Gulgenova.

Scutisotoma baica Potapov, Babenko & Fjellberg, 2006: Buryat Republic, SE shore of Lake Baikal, at Ust’ -Barguzin, 53.4086°N, 108.9879°E, floatation of wet sand at water edge, 05.VIII.2014, coll. M. Potapov and A. Gulgenova.

Isotomurus stuxbergi (Tullberg, 1876): Buryat Republic, SE shore of Lake Baikal, 5 km N from Turka, 14.V.2017, coll. A. Gulgenova and S. Gulgenov.

Other new records of species concern shores of saline lakes and therefore are given in the Table of Appendix 1.

Faunistic notes

Three ecological groups can be recognised among the recorded species:

Species widely distributed in the Holarctic and living also at sites distant from the lake shore (notated as W in Appendix 1). This group mostly consists of xerophilic and steppe species (e.g., F. parvulus, A. stebayevae, A. mongolicus, F. mongolica sp. nov.) which occur also on neighbouring arid landscapes of continental Asia. They often prefer saline lands and penetrate to catenas of saline lakes where they can be numerous. The group also include widely distributed eurytopic (P. notabilis, P. minima) and ruderal species (P. minuta). The latter species can be very abundant in lower part of catenas.

Lake species (as L in Appendix 1). This group consists of species found so far only in lake shores. They mostly belong to the fauna of Lake Baikal (P. barathrum sp. nov., S. acorrelata, S. baica, S. robustodens, P. appressopilosa, P. baicalica sp. nov.). Folsomia uniramia presumably belongs to the group since it has been recorded only in dunes at this lake shore. S. acorrelata and P. appressopilosa also occur in shore of saline Alginskoye Lake which is close to Baikal Lake. Considering salt-lake catenas, E. buryatica sp. nov. is only species which belongs to this group.

Hygrophilic widely distributed species (as H in Appendix 1). In our materials, Isotomurus stuxbergi (Tullberg, 1876) is the only member belonging to this group. It was found once in the Baikal shore.

Figures

Figure 43. Appearance of Parisotoma baicalica sp. nov.

Figures 44 - 57. Parisotoma baicalica sp. nov. (44 - 50), (52 - 55) and P. reducta (51, 56) 44 s-, ms-setae, and macrosetae on body 45 macroseta of Abd. V 46 PAO and ocellus 47 Ant. 1, lateral view (s and ms shown) 48, 49 postlabial setae, variation 50, 51 papilla E of labial palp, lateral view 52 papilla B, ventral view 53 mucro 54 ventral tube, lateral view 55 apical part of Leg 3 56, 57 posterior side of dens. Abbreviations: s-s-seta, ms-micro s-seta, bms-basal micro s-seta, l. p. - lateral processes, b. p. - basal processes, B, E-papillae of labium, int, ext-internal and external setae of posterior side of dens.

Figures 6 - 11. Pseudanurophorus barathrum sp. nov. 6, 7 s-setae on body in one variant 8 PAO and Ant. 1, lateral view 9 Ant. 3 (only sockets shown for setae, additional s-setae on inner side of segment not shown), lateral view 10 apex of Ant. 4 (pin-seta, organite, and subapical ms shown) 11 apical part of Leg 2. Abbreviations: bms-basal micro s-seta, sms-subapical micro s-seta, org-organite, pin-pin-seta, s-s-seta, ms-micro s-seta, PAO-postantennal organ, is, ls, os-inner, lateral, and outer s-setae of antennal organ.