Ceratophysella dobrolyubovae, Babenko & Antipova, 2025

Ceratophysella dobrolyubovae sp. nov.

Figs 1–12 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURES 4–7 View FIGURES 8–17 , 18–31

Type material. Holotype male, Russia, Northwest Caucasus , Karachay-Cherkess Republic , Dombai, 400–500 m off Alibek Glacier, 43.2964°N, 41.5476°E, 2110 m alt., birch-willow shrubland ( Figs 1–2 View FIGURE 1 View FIGURE 2 ), pitfall traps, 15– 25.07.2024, M. Antipova leg. Deposited in MSPU. GoogleMaps

Paratypes 2 males & 2 females, 15 juv. same area, ~370 ind. in ethanol.

Additional material. 3 females, 1 male and 2 juveniles, Russia, Northern Caucasus, Republic of North Ossetia – Alania, Tsey glacier foreland, pitfall traps at the glacier edge, 42.7753°N 43.8609°E, ~ 2320 m alt., 22– 28.07.2021. O. Makarova, M. Antipova & A. Babenko leg. GoogleMaps ; 2 females, same region, but rocky river floodplain in forest belt 42.7933°N, 43.9239°E, ~ 1700 m alt., O. Makarova leg.; 9 females, 6 males and 4 juveniles, hundreds of specimens preserved in ethanol, collected using pitfall traps, Kabardino-Balkarian Republic, Cherek Bezingiisky (Khulamsky) River valley, Bezengi glacier foreland, 43.10635°N, 043.13156°E, 2044–2165 m alt., various sites, but most abundant on the 14-year old deglaciated surface, the stony mound dominated with Vicia alpestris and Chamaenerion colchicum , 20– 30.07.2022. M. Antipova & A. Babenko leg. GoogleMaps ; 9 females, 4 males and 6 juveniles, same region, Irik River valley , ~ 3000 m alt., alpine meadow, 24.09.1999. A. Babenko leg. ; 9 specimens, same area, data and collector, but ~ 2900 m alt., dense moss and grass cover on rock; 4 specimens, same area and collector, but Adylsu River valley , ~ 2300 m alt., organic debris in willow hollow, 25.09.1999 ; 1 female, same area, Baksan River valley, below Ulybka Shkheldy Glacier , ~ 2350 m alt., N. Morozova leg. ; 9 females, 2 males and 1 juvenile, same area, Mount Elbrus , ~ 3000 m alt., sedge association, 07.06.2018. O. Makarova leg. ; 2 males, 1 female, 1 juvenile, same area, 3500 m alt., mosses on the rocks, 26.07.2023 M. Antipova leg. 1 female, 1 male and 3 juveniles, ~200 ind. in ethanol, same area, Adylsu River valley, Kashkatash glacier foreland, 43.211484°N, 42.686428°E, 2520 m alt., young willow-birch forest, 74 years after glacier retreat, pitfall traps and Tullgren funnels, 16.07– 3.08.2023, M. Antipova & A. Babenko leg. GoogleMaps

DNA material. COI barcode sequences were obtained from four glacier forelands mentioned above: Bezengi (3 ind.), Kashkatash (3 ind.), Alibek (5 ind.) and Tsey (5 ind.). The sequences have been deposited in GenBank under accession numbers PX505022–PX505037.

Diagnosis. A relatively small-sized species of the denticulata - group, characterised by the fine and almost uniform cuticular granulation, the number of thickened sensilla on Ant. IV usual for the genus, a complete set of papillae on the labium, a virtually complete chaetotaxy with fine curved microsetae and short, straight and usually serrated macrosetae that taper only close to their tips. Apart from the distinctive chaetotaxy, its most striking feature is the presence of a complete set of papillae on the labium.

Description. Body length without antennae 0.9–1.1 mm, holotype — 1 mm. Habitus typical of the genus. General body colour in alcohol ranging from bluish to brownish ( Fig. 3 View FIGURE 3 ), with diffuse dorsal pigmentation and a paler ventral side. Granulation of integument rather fine and more or less uniform, sometimes a little coarser in the mid part of Abd. V, with 8–14, usually 10 granules between setae p1.

Antennal segments subequal in length to head. Ant. IV usually with a slightly divided apical bulb, seven blunt curved sensilla (five dorsal, S0, S1–S4 and two dorsolateral (external), S7 and S8), well differentiated from common setae; subapical organite (or) and microsensillum (ms) present as usual ( Fig. 19 View FIGURES 19–30 ); ventral sensory file with few short blunt setae, some of which slightly capitate ( Fig. 20 View FIGURES 19–30 ). Eversible sac between Ant. III and Ant. IV quite small and barely noticeable. Ant. III with a typical AO ( Fig. 20 View FIGURES 19–30 ), ms on outer side present. Ant. I–II with 7 and 13 smooth common setae, respectively, inner ones slightly longer as usual.

Head with 8+8 subequal eyes ( Figs 4–5 View FIGURES 4–7 ). PAO 2.5–2.8 times larger than adjacent ocellus, consisting of two long anterior and two smaller posterior lobes, an accessory boss present ( Fig. 22 View FIGURES 19–30 ). Labrum with 4/554 setae, its distal edge without distinct papillae as usual. Labial palp of the denticulata type with 6 proximal setae, all common papillae (A, B, D, E and C) and 14 guards, among them a1, b1, b2, d2, and e2 short, a1 rod-shaped, a lateral process (lp) small ( Figs 6 View FIGURES 4–7 , 23 View FIGURES 19–30 ). Basomedial field of labium (submentum) with four setae, basolateral one (mentum) with five setae, as usual. Head with 3+3 postlabial setae along ventral line. Maxillary head of the denticulata - type with three teeth on main part and six usual lamellae, L.1 extending beyond tip of maxillary teeth and slightly expanded at apex ( Fig. 18). Outer maxillary lobe simple, with one sublobal hair.

Dorsal chaetotaxy typical of the denticulata - group, dorsal setae short and clearly differentiated into curved microsetae and short, straight and usually serrated macrosetae ( Figs 8–9 View FIGURES 8–17 ). The latter usually more or less rod-shaped, tapering only at the tips ( Figs 10–12 View FIGURES 8–17 ), sensorial setae about as long as macrosetae, on Abd. V usually longer ( Fig. 12 View FIGURES 8–17 ). Main peculiarities of tergal chaetotaxy: Th. II–III with most setae in a-row (excluding a3 on Th. II) as microsetae of similar length; m3 on Th. II present only occasionally and always absent from Th. III, as usual for the genus; macrosetae p2 slightly thinner and longer than p3; a lateral ms present on Th. II. Abdominal chaetotaxy ( Fig. 9 View FIGURES 8–17 ): Abd. I–III with a2’ and m3–m4 present; position of a1 setae relative to midline on Abd. IV rather variable; Abd. V without a2’, i.e. only 3 a-setae present between bases of macrosetae p1 and p5.

Chaetotaxy of legs 1–3 stable and typical of the genus: upper subcoxae—1, 3, 3 (among them, one macroseta on each subcoxa); lower subcoxae—0, 3, 3; coxae—3, 8, 8; trochanters—7, 7, 7; femora—14, 13, 12; tibiotarsi—19, 19, 18 setae, respectively. Tibiotarsal tenent setae (A1) acuminate, as a rule, rarely blunt or even slightly widened at apex, about as long as or slightly shorter than inner unguis edge ( Fig. 29 View FIGURES 19–30 ). Unguis with a small tooth in midsection of inner edge and a pair of lateral teeth basally ( Figs 28–29 View FIGURES 19–30 ). Unguiculus slightly shorter than half unguis inner edge, with a distinct basal lamella.

Ventral tube with 4+4 distal setae. Retinaculum with 4+4 teeth. Furca well-developed. Dens with six equally thick dorsal setae; outer basal macroseta about 0.7–0.9 × as long as dens ( Figs 7 View FIGURES 4–7 , 24, 26 View FIGURES 19–30 ), area without visible granulation on ventral surface of dens rather large ( Fig. 25 View FIGURES 19–30 ). Mucro of usual shape with a high, triangular, outer lamella, 1.6–2.1 × as long as dens.

Anal spines light and curved, borne by high papillae ( Fig. 30 View FIGURES 19–30 ), together with papilla clearly longer than inner unguis.

Epitoky. Epitokous changes in the morphology of the adult individuals of C. dobrolyubovae sp. nov. are clear, but not very pronounced. The modifications observed are quite consistent with those described for representatives of the genus ( Cassagnau 1964b, Bourgeois 1971, 1974, 1981; Bourgeois & Cassagnau 1973; Waltz & Hart 1986; Zettel & Zettel 1994; Skarżyński 2000): individuals in the reproductive stage show a clearly shortened furca ( Fig. 27 View FIGURES 19–30 ), the eversible sac between Ant. III–IV reduced, and the sensilla in the ventral sensory file are less noticeably modified ( Fig. 21 View FIGURES 19–30 ). In addition, the buccal cone in the reproductive stage is noticeably flattened while the long guards on the labial palp are clearly shortened and thickened.

Etymology. Named in honor of Tatiana Dobrolyubova, who first recorded this species (as C. succinea ) from this region during her long-term studies (1975–1992) of the collembolan fauna in the Northwest Caucasus.

Affinities. The most noticeable feature of C. dobrolyubovae sp. nov. seems to be the partial reduction of dorsal setae on the dens. The structure of the furca is a very stable feature of the genus. However, of 146 species of the world fauna ( Bellinger et al. 1996 –2025), more than 14% show some degree of its reduction. Five of such species have been described from North and Central America, i.e. C. densornata ( Maynard, 1951) ; C. orizabae Yosii, 1962 ; C. scotti Yosii, 1962 ; C. sedecimocellata Yosii, 1962 and C. engeli Ellis, 1968 . Four species ( C. proserpinae ( Yosii, 1956) ; C. kutyrevae ( Babenko, 1994; in Babenko et al. 1994); C. zhangi (Zhao, 1998; in Tamura & Zhao 1998); and C. taiguensis Jia, Skarżyński & Li, 2010 are known from the Far Eastern regions of the Palaearctic. Ceratophysella czukczorum Martynova & Bondarenko, 1978 , a complex of closely related forms, inhabits the Beringian region on both sides of the Bering Strait. The identity of all these species, many of which are insufficiently well described, with C. dobrolyubovae sp. nov. is questionable simply because of the latter’s very distant occurrence. Among the species listed, C. dobrolyubovae sp. nov. seems to be particularly similar to C. zhangi (the description of which was based on a single and probably immature specimen ( Jia et al. 2010)) and C. taiguensis . Of these two species, the former one is distinguished by the short unguiculus (~ 1/3 U3) and the unguis without teeth, while the latter, on the contrary, shows an elongated unguiculus (~ U3).

The fauna of Europe is the richest in species that have a reduced number of setae on the dens: four such species of the armata -group, i.e. C. quinquesetosa ( Gisin, 1958) ; C. cylindrica Cassagnau, 1959 , C. penicillifer Cassagnau, 1964 and C. sextensis Cassagnau, 1968 , and at least seven species of the denticulata - group, C. succinea ( Gisin, 1949) ; C. norensis Cassagnau, 1964 (1964a); C. varians ( Stach, 1967) ; C. kapoviensis ( Babenko, 1994; in Babenko et al. 1994); C. vargovychi Skarżyński , Kaprus’ & Shrubovych, 2001; C. michalinae Skarżyński, 2005 and C. robustiseta Skarżyński & Smolis, 2006 . There is also one “forgotten species”, C. sphagni ( Becker, 1905) ( Moscow Region, Russia), which also has six, not seven, setae on the dens and may well be a senior synonym of C. succinea . Within the denticulata - group, two species ( C. succinea and C. michalinae ) can easily be distinguished from C. dobrolyubovae sp. nov. by the absence of papillae C from the labial palp. The same is also characteristic of C. kapoviensis [new data]. Unlike the new species, C. norensis (mountainous regions of southern France) is characterised by a noticeable reduction of dorsal chaetotaxy, in particular the presence of only 2+2 axial microsetae on Abd. IV. For both C. varians ( Malta) and C. robustiseta ( England, but from an artificial substrate in a botanical garden), the presence of only 6 setae on the dens is rather an exception than a rule, since in both cases the dens in the figures shows 7 setae. In addition, the former species has dorsal macrosetae smooth, on the last tergites being about as long as those tergites ( vs clearly shorter and usually serrated in C. dobrolyubovae sp. nov.). Ceratophysella robustiseta is characterised by four primary lobes of the postantennal organ with more or less numerous fingershaped papillae, as well as both macro- and microsetae being thick, abruptly pointed at tips and clearly serrated, a long unguiculus and a very long basal seta on the dens ( vs normal lobes in PAO, a clear difference in the shape of the macro- and microsetae, a shorter unguiculus and a shorter basal macroseta on the dens in C. dobrolyubovae sp. nov.).

Among the European species compared, C. vargovychi inhabits an area (the Crimean Peninsula) relatively close to the Caucasus, but it has been found only in caves. It differs from C. dobrolyubovae sp. nov. by the larger size (up to 2.1 mm), the relatively light colouration, the significantly longer dorsal setae and the unguiculus exceeding half the inner edge of the unguis. In addition, in C. dobrolyubovae sp. nov., most setae of the a-row on Th. II excluding a3 are microsetae subequal in length, whereas in C. vargovychi both setae a2 and a3 are differentiated as typical macrosetae.

Remarks. In one of the Caucasian regions ( North Ossetia – Alania, the Tsey River Gorge), two superficially similar forms have been found, both differing only in the level of dorsal setae differentiation (cf. Figs 13–17 View FIGURES 8–17 & Figs 8–12 View FIGURES 8–17 ). The short-setae form, described above as C. dobrolyubovae sp. nov., was found mainly in the alpine belt (lower only in the rocky floodplain near streams), whereas the second form, which had longer and thinner setae (see Figs 13–14 View FIGURES 8–17 ) was recorded only in forest communities. Initially, we assumed these were two different forms of the same species and their differences were directly related to the harsher living conditions encountered by the high-mountain form. As similar polymorphism has previously been noted in the genus Ceratophysella , albeit in the armata -group ( Skarżyński 2003), there was nothing extraordinary in such an assumption. However, molecular studies have revealed considerable genetic divergence between these forms ( Fig. 31 View FIGURE 31 ). The Kimura 2-parameter (K2P) pairwise distances for the COI gene range from 19% to 21% ( Table 1), corresponding to interspecific variation levels typical of Ceratophysella ( Skarżyński et al. 2021; Jia et al. 2024; Salimi et al. 2025). This strongly suggests they represent distinct species. Although typical representatives of a given form are easily distinguishable, there are also intermediate variants that are difficult to clearly assign to either form. Moreover, in the available old material from different regions of the Greater Caucasus and Transcaucasia, further several forms seem to be represented, the morphological differences of which are minimal. At present, we are forced to consider them as a complex of closely related forms of unclear status ( C. sp. aff. dobrolyubovae ) and can only state a highly diverse complex in the fauna of the Caucasus.

Distribution and ecology. The new species appears to be endemic to the Caucasus region, distributed at least from Teberda in the west to North Ossetia – Alania in the east ( Fig. 1 View FIGURE 1 ) and found primarily in alpine highlands ( Fig. 2 View FIGURE 2 ).