Pseudanurophorus barathrum 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

Pseudanurophorus barathrum Potapov & Gulgenova sp. nov. Figures 1-5 , 6-11 , 12-13

Type material.

Holotype: female. Buryat Republic, Severo-Baykalskiy District, ~ 30 km N Severobaykalsk, near Slyudanskoye Lake, 55.4627°N, 109.1698°E, shingly beach of Baikal, 17.VIII.2013, coll. M. Potapov and A. Gulgenova. 5 paratypes from the same place (Holotype and 2 paratypes deposited in MSPU, 3 - in SMNG). 2 paratypes from Russia, East Siberia. Irkutskaya Region, Slyudyanskiy District, Slyudyanka, shore of Lake Baikal, 51.6529°N, 103.7350°E, on moistened big stones (by aspirator), 29.VIII.2008, coll. M. Potapov (deposited in BSU).

Other material.

Irkutskaya Region, Slyudyanskiy District, Angasolskaya, shore of Lake Baikal, 51.7314°N, 103.8280°E, in shingle, 09.VIII.2015, coll. G. Efanov; Irkutskaya Region, Irkutskiy District, shore of Baikal, Primorskiy Range, Pribaikal’skiy Nat. Park, Khargino, 52.320°N, 105.776°E, stony beach, near water edge (by aspirator), 17.VIII.2013, coll. A. Babenko; Irkutskaya Region, Olkhonskiy District, Primorskiy Range, Kuyada, mouth of Talovka River, 52.553°N, 106.136°E, stony beach, under stones, 15.VII.2013, coll. A. Babenko; Buryat Republic, Kabansky District, Posolskiy Sor Bay, near Baykalskiy Priboy, 51.91216°N, 106.13954°E, seaweed debris near water, 23.VII.2011, coll. A. Chimitova and L. Vanyavina; 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. The materials are deposited in MSPU and SEM.

Description.

Size 1.0-1.5 mm. Body broad, with long legs (Fig. 1 ). Pigmentation from almost white to pale grey, forming a diffuse net interrupted by intersegmental areas. Cuticle finely reticulated ( “smooth”), size of polygons much smaller than bases of setae. Large specimens sometimes with regularly scattered hardly visible small pits. Lateral parts of intersegmental area with secondary granulation (Fig. 6 ). Ocelli absent. PAO small, not constricted, ca. 0.3 as long as Ant.1 width and ca. half as long as U3 (Fig. 8 ). Maxillary outer lobe with simple maxillary palp and four slender sublobal hairs (Figs 2 , 3 ). Labral formula as 3/556 (Fig. 3 ). Labral edge reduced, apical ridges absent. Apical row (p-row) of labral setae projecting above mouth aperture (Figs 2 and 3 ), normally with six setae: p1, p2, and p3 on each side, lateral pair (p3) more slender and long. Medial pair p1+p1 is sometimes replaced with one (p0) giving five setae (p0, p1, p2) in apical row and labral formula 3/555 (Fig. 3 ). Setae of two rows (m, p) of labrum and sublobal hairs form a basket surrounding the mouth. Labium with all papillae (A-E), papillae A without guards (Fig. 4 ). Guard a1 detached and integrated to papilla B which, in result, supplied with five guards (a1, b1-4). Guards b2, b3, b4 set together, on lateral expansion of papilla B. Papilla C without guards, D with four guards in normal position. E with seven guards, lateral process and two lateral guards enlarged. Terminal setae of all papilla short. All elements of hypostomal group (H, h1, h2) considerably enlarged and bent towards labrum complementing the upper “basket” (Figs 2 , 4 ). Main part of labium with three proximal, four basomedian and five basolateral setae. Maxillary head modified: capitulum slender and formed by fused claws, lamellae enlarged. Lamellae 1 and 2 well beyond capitulum, each supplied with apical and inner rows of cilia. Outer edge of lamella 1 gently ciliated, sometimes wavy. Lamella 3 expanded, with strong teeth (Fig. 5 ). Ventral side of head with 5-6+5-6 postlabial setae. S-setae and bms-setae of antennae slender and resemble common setae. Ant.1 with two basal, ventral and dorsal, bms, two ventro-lateral s, and ca. 30-40 common setae (Fig. 8 ). Ant.2 with three bms and one laterodistal s. Ant.3 with one bms, five common s (two outer, two inner, and one lateral spine-like), and a group of additional thin s-setae located on dorsal and inner sides of segment (Fig. 9 ), inner additional s-setae hardly differ from common setae. S-setae on Ant.4 weakly differentiated, subapical organite rudimental, apex without bulb (Fig. 10 ).

Body with numerous smooth short setae. Dorsal axial setal pattern asymmetric, can approximately be described as: 12-14,11-14/9-10,9-10,9-10,12-14 (Th.II-Abd.IV). Macrosetae not differentiated. S-setae on tergites weakly differentiated, subequal to common setae (Fig. 13 ). S-setae varies as 4,4-5/3-5,4-5,4-6, ~9, ~10, number and arrangement asymmetrical. With incomplete set of ms-setae (1,0/0,0,1). Most s-setae on Abd.I-Abd.V in p-row of setae (Figs 6 , 7 , 13 ). Th.I, II, and III without ventral setae.

Unguis rather slender, without teeth (Fig. 11 ). Empodial appendage with lamellae, without teeth. All tibiotarsi with many additional setae, ca. 40 on Ti.1 and Ti.2 and 50-60 on Ti.3. Adult male often with slightly swollen Ti.3, with stick-like thin spurs (x and B5). Tibiotarsi of all legs with seven setae in apical whorl. Tibiotarsal tenent setae pointed (Fig. 11 ). Ventral tube with 12-14+12-14 distal and ca. 20 posterior setae, without anterior setae. Distal setae in two groups, anterior (9-11+9-11) and posterior (3+3). Tenaculum and furca entirely absent. Tenacular field with ca. 20-30, manubrial field with ca. 40-50 setae (Fig. 12 ). Manubrial setae in anterior and posterior groups. Anterior furcal subcoxae with 13-16 setae, posterior subcoxae with 18-20 setae. Posterior subcoxa weakly separated from setaceous part of segment. Males present.

Affinity.

This remarkable species is characterised by two (more rarely one) additional setae on labrum that is so far unknown in Pseudanurophorus Stach, 1922 and other Collembola as well. Labral formula 5,5,4 (vs. 5,5,5-6 in P. barathrum sp. nov.) is invariable in Isotomidae and it is clear that the character is often omitted although being implied in the descriptions. Other mouth parts are also strongly modified: labral edge is reduced; two anterior setal rows and the sublobal hairs form a basket surrounding the mouth; hypostomal setae and lateral process are enlarged; guard a1 is integrated with papilla B; guards b2, b3, b4 set on lateral expansion of B; maxillary head has slender capitulum and expanded lamella. Unusually high number of setae on tibiotarsi and ventral tube and the dense and short abdominal hair cover is an apparent adaptation to live in close contact with water, as in many other littoral species.

The new species belongs to the " boerneri " group due to three prelabral, 4+4 or more postlabial setae, simple maxillary palp and other characters (for details see Potapov 1997). It most resembles two species with short macrosetae P. arcticus Christiansen, 1952 and P. montanus Martynova, 1971 (1971a), for which labral formula is unknown. Following the first description and Fjellberg’s comments (1975) on P. arcticus paratypes, these two species have much fewer setae in axial group of tergites and yet have macrosetae on last abdominal segments (vs. absent in P. barathrum sp. nov.). Pseudanurophorus arcticus is described and subsequently recorded in the Arctic and P. montanus in the mountains of Middle Asia.

Distribution and ecology.

Several records from the littoral zone of the shore of Lake Baikal, none found inland. It is one of the common species in shingly beaches.

Name derivation.

It is named after the specific mouth parts ( barathrum - a glutton in Latin, among other translations).

Figures

Figures 1 - 5. Pseudanurophorus barathrum sp. nov. 1 appearance of dark coloured specimen 2 labrum, maxillary outer lobe and hypostomal setae, lateral view 3 labrum and maxillary outer lobe, fronto-ventral and ventral views 4 labium, ventral view 5 maxillary head. Abbreviations: A, B, C, D, E-papillae of labial palp, H, h 1, h 2 - hypostomal setae, mo, m 1, m 2, p 1, p 2, p 3 - setae of m - and p-row of labrum, mx. ol-maxillary outer lobe, cap., 1 - 6 - capitulum and lamellae 1 - 6 of maxillary head, a 1, b 1, b 2, b 3, b 4, e 7 - labial guards, l. p. - lateral processes. Characters of greater value encircled.

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.

Figures 12, 13. Pseudanurophorus barathrum sp. nov., chaetotaxy of ventrum of Abd. III-VI (12) and dorsum of Abd. IV-VI (13) Abbreviations: ten. a. - tenacular area, man. f. - manubrial field, ant. scx, post. scx-anterior and posterior subcoxae, s-s-seta.