Arrhopalites colchicus, Vargovitsh, 2025

Arrhopalites colchicus sp. nov.

Figs 3–7 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 , Tables 1–3 View TABLE 1 View TABLE 2 View TABLE 3

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Diagnosis (female). Body unpigmented, 0.9 mm long. Eyes not detectable. Setae of head dorsum slender, 3 axial present. Antenna about 2× of head; Ant III with well-developed sense organ; Ant IV subdivided into 6 subsegments weakly separated from each other by 1–3 annuli, with 14 whorls of setae. Trochanter I, II and III with 4, 4, 5 setae. Femur I, II, III with 11, 13, 12 setae. Tibiotarsus I, II, III with 42, 41, 44 setae. Claws slender and extremely elongated, without tunica and without inner tooth; empodia short, without corner tooth. Manubrium with 5 + 5 setae. Dens without distinct spines, posterior side with 16(15) and anterior side with 3, 2, 1, 1, 1 setae, Ia weakly spine-like. Mucro with small slightly knobbed apex, edges of posterior lamellae partly accreted. Trichobothria ABC form about right angle. Posterior setae of great abdomen 4× longer than anterior. Sixth abdominal segment with ordinary smooth not broadened circumanal setae; dorsal valve with 11 + 2 axial setae per side, lateral valve with 16 setae; appendices anales rod-like, smooth, acuminate and apically curved. Belongs to Arrhopalites caecus group of species s. str. ( Vargovitsh 2013).

Type material. Holotype on slide C-1036a-1: female, W Caucasus, Abkhazia, Sukhum District, Verkhniaya Eshera Vill., Verkhneesherskaya Cave (N 43° 04′ 34″; E 40° 58′ 33″; 540 m a.s.l.), ~ 400 m distance and 60 m depth from entrance, on water surface, 20.vii.2016, R.S. Vargovitsh leg. GoogleMaps Paratype on slide C-1036a-2 ( Fig. 6A View FIGURE 6 ): male, collected together with holotype from the same cave and by the same collector. The holotype and paratype are preserved in the collection of the Schmalhausen Institute of Zoology, National Academy of Sciences of Ukraine, Kyiv GoogleMaps .

Description. Female. Body length 0.9 mm, unpigmented (see Table 1 View TABLE 1 and 2 View TABLE 2 for other measurements).

Head ( Fig. 3A View FIGURE 3 ). Eyes not detected. Clypeal area includes six rows a to f with 4 + axial + 4 / 5 + 5 / 5 + 5 / 5 + 5 /5 + 5 / 6 + 6 setae respectively, and median region M with 4 asymmetrical setae. Interantennal area: row α: 2 + 0 (variable), row β: 1 + axial + 1. Dorsal area with four rows (A to D) with 1 + 1 / 1 + axial + 1 / 2 + axial + 2 / 2 + 2 setae respectively; all setae of head dorsum slender ( Figs 4D View FIGURE 4 , 6B View FIGURE 6 ). In total, head dorsum bears 3 axial setae ( Figs 3A View FIGURE 3 , 6B View FIGURE 6 ). Head axial setae (labral, clypeal and dorsal) marked in black in Fig. 3A View FIGURE 3 . Chaetotaxy of the head posterior side as in Fig. 3A View FIGURE 3 (dotted circles).

Chaetotaxy of mouth region. Labrum ( Figs 3A View FIGURE 3 , 6E View FIGURE 6 ): labral (a m p) / prelabral chaetotaxy: 4 5 5 / 6; setae of a-row situated on four labral papillae. Labium: submentum with 4 setae, mentum with 5 setae ( Fig. 6F View FIGURE 6 ); labial palp ( Fig. 3C View FIGURE 3 ) with 5 proximal setae, 5 papillae (A, B, C, D, E) with deeply inserted setae and with 13 associated guard setae (a1, b1–4, d1–4, e1–4 of which a1 is blunt and strongly curved) and 3 hypostomal setae (H, h1, h2). Maxilla head as in Fig. 6G View FIGURE 6 . Maxillary outer lobe ( Figs 3D View FIGURE 3 , 6E View FIGURE 6 ): apical seta of the maxillary outer lobe with short subparallel branch at the base, sublobal plate with three sublobal hairs. Oral fold with 2 setae ( Fig. 6E View FIGURE 6 ).

Antenna ( Fig. 3B View FIGURE 3 ) 1.9× of head. Length ratio of antennal segments I / II / III / IV = 1 / 2 / 3 / 7.4. Ant I with 7 setae, p as microseta (5.3 μm). Ant II with 14 setae. Ant III without swelling, with following chaetotaxy: 15 simple setae, especially thin Api and Ape setae, 2 well developed sensory rods (11.6 μm) in shallow pits and Aai as small (4 μm) blunt sensillum ( Fig. 6D View FIGURE 6 ); 20 setae in total. Ant IV indistinctly subdivided into 6 subsegments separated from each other by 1–3 weakly developed and hardly visible annuli. Subsegmental formula: 1 + 4 + 1. Ant IV bears 14 whorls of setae: 4 on apical subsegment (A1–A3 + M1–M2), 4 on median subsegments (M3–M6) and 5 on basal subsegment (BA + BM1–BM3 + BB).

Legs. Foreleg ( Fig. 4A View FIGURE 4 ): precoxae 1, 2 and coxa with 1, 0, 1 setae respectively. Trochanter with 3 anterior and 1 posterior setae. Femur with 11 setae, a4 turned perpendicularly to the longitudinal axis of the segment. Tibiotarsus with 42 setae, tibiotarsal formula: 9, 8, 8, 8, 6, 3; seta Ja of distal whorl I curved and moderately spine-like; whorl V without ai and pi setae; region F with primary setae e, ae, pe. Pretarsus with 1 anterior and 1 posterior setulae. Foot complex ( Fig. 7C View FIGURE 7 ). Claw: slender and much elongated (91 μm), without tunica, without inner tooth, with a pair of long subapical lateral teeth; about 2.2× shorter than tibiotarsus. Empodium: thin, without corner tooth; very short (1.9× shorter than claw); tip of empodial filament far not reaching tip of claw.

Mid leg ( Fig. 4B View FIGURE 4 ): precoxae 1 and 2 with 1, 1 setae respectively, precoxal process present, coxa with 3 setae and one microsensillum ( Fig. 5A View FIGURE 5 ). Trochanter with 4 setae: anterior trochanteral organ, 2 anterior and 1 posterior simple setae. Femur with 13 setae. Tibiotarsus with 41 setae (9, 8, 8, 8, 5, 3); Ja curved and moderately spine-like, whorl V without ai and pi setae; region F with primary setae e, ae, pe. Pretarsus with 1 anterior and 1 posterior setulae. Foot complex ( Fig. 7D View FIGURE 7 ). Claw: slender and much elongated (92 μm), without tunica, without inner tooth and a pair of long subapical lateral teeth; 2.1× shorter than tibiotarsus. Empodium: thin, without corner tooth; very short (2× shorter than claw); tip of empodial filament far not reaching tip of claw.

Hind leg ( Fig. 4C View FIGURE 4 ): precoxae 1 and 2 with 1, 1 setae respectively, process on precoxa 1 present, coxa with 3 setae and one microsensillum. Trochanter with 5 setae: anterior trochanteral organ, 3 anterior and 1 posterior simple setae. Femur with 12 setae, 2 posterior ones (p1 and p3) as microsetae. Tibiotarsus with 44 setae (9, 8, 8, 8, 7, 4); Ja of whorl I as simple seta, region F with primary setae e, ae, pe and secondary seta FSa. Pretarsus with 1 anterior and 1 posterior setulae. Foot complex ( Fig. 7E View FIGURE 7 ). Claw: slender and elongated (81 μm) but shorter than claw I and II, without tunica, without inner tooth, with pair of relatively long subapical lateral teeth; about 2.7× shorter than tibiotarsus. Empodium: broad, without corner tooth; 1.6× shorter than claw; tip of empodial filament not reaching tip of claw. Lengths ratio of tibiotarsi I / II / III = 1 / 1 / 1.1. Tibiotarsi about 1.6× shorter than head.

Ventral tube with 1 + 1 subapical microsetae.

Tenaculum ( Fig. 5C View FIGURE 5 ): each ramus with 3 teeth and basal process; anterior lobe with 1 seta.

Furca ( Fig. 5B View FIGURE 5 ). Manubrium with 5 + 5 posterior setae. Dens with 23–24 setae (8 anterior and 15–16 posterior). 3, 2, 1, 1, 1 setae on anterior side, Ia–IVa, Ba and IIae somewhat thickened, Ia weakly spine-like ( Fig. 4K View FIGURE 4 ). Posterior side without spine-like setae, Vpe variable (present on one and absent on other dens). Mucro ( Fig. 7F View FIGURE 7 ): posterior lamellae with teeth partly accreted together, margins look partly wavy or serrated; anterior lamella smooth and well developed; tip rounded or spoon-like but not broadened. Dens 2× as long as mucro ( Table 2 View TABLE 2 ).

Great abdomen ( Fig. 5A View FIGURE 5 ). Each of segments Th II and III bearing single bent sensillum in row a (13–14 μm) ( Fig. 4F View FIGURE 4 ) and 3 setae in row m with m1 ( Fig. 4E View FIGURE 4 ) 3–4× shorter than most posterior setae (dI–dIII)-1 of posterior dorsal complex ( Fig. 4G View FIGURE 4 ). Anterior part of abdomen with row a (5 setae), row m (4 setae) and seta p. Trichobothrial complex ( Figs 5A View FIGURE 5 , 7A View FIGURE 7 ): ABC form an angle close to right (74°; 94°) and AB is 1.2× longer than BC; seta p is located above the level of trichobothrium B; seta b1 lies on line BC, closer to C; seta c1 (25 μm) thinner and shorter than c2 but not as microseta, c1 lies in front of trichobothrium C and seta c2—below C. Posterior lateral complex with 5 setae in two rows (2 + 3) and furca base complex with 8 setae in two rows, neosminthuroid seta absent. Central dorsal complex with seta 3 smaller than 1 and 2 ( Fig. 7A View FIGURE 7 ). Posterior dorsal complex with 18 long setae arranged in 3 longitudinal rows dI–dIII with 6 / 6 / 6 setae respectively, the longest of which (the most posterior setae of rows dI–dIII) = 68 μm is shorter than hind claw ( Tables 1 View TABLE 1 , 2 View TABLE 2 ). Ventral complex is variable, with one seta on one side of body ( Fig. 5A View FIGURE 5 ) and two on the other (not shown in Fig. 5A View FIGURE 5 ).

Small abdomen. Fifth abdominal segment ( Fig. 5A View FIGURE 5 ) with 2 setae and trichobothrium D in row a, and 2 setae in row p. Genital field with 2 + 2? microsetae along anterior margin of genital opening.

Sixth abdominal segment ( Figs 5D View FIGURE 5 , 7B View FIGURE 7 ) without any cuticular spines. Dorsal valve with 11 + 2 axial + 11 setae. Each of lateral valves ( Fig. 7B View FIGURE 7 ) bears 16 setae, seta mpi2 of circumanal row absent. Setae of circumanal row slender and not modified, the longest = 45 μm, that is 1.5× shorter than posterior setae of great abdomen ( Fig. 4H View FIGURE 4 ). Appendices anales ( Figs 4I–J View FIGURE 4 ; 7B View FIGURE 7 ) (24 μm) rod-like, smooth, apically curved and acuminate; sitting on globular basal papilla.

Male. 0.85 mm length, slightly smaller than female ( Fig. 6A View FIGURE 6 ). Antenna 2.1× of head, Ant IV with 7 subsegments separated from each other by 2–4 annuli which are more distinct than in female ( Fig. 6C View FIGURE 6 ). Both dens with complete set of setae (8 anterior and 16 posterior). Small abdomen ( Fig. 5E View FIGURE 5 ): dorsal anal valve of Abd VI with 7 + 2 axial +7 setae, ventral valve with 15 setae each, genital opening surrounding with 9 + 9 short setae. Whorl V of left and right tibiotarsus III with 5 and 6 setae respectively. Otherwise, male chaetotaxy corresponds to females; for measurements see Tables 1 View TABLE 1 and 2 View TABLE 2 .

Variability. In female: interantennal area is aberrantly incomplete on the left side (row α: 2 + 0); ventral complex of great abdomen with 1 or 2 setae per side; dens seta Vpe present or absent. In male arrangement of left and right interior dens surface is different: normal 3, 2, 1, 1, 1 and aberrant 3, 1, 2, 1, 1.

Ecology and distribution. Two specimens of Arrhopalites colchicus sp. nov. were found on the water surface in pools along the cave stream at a depth of 65 m, approximately 400 m from the entrance of Verkhneesherskaya Cave (Upper Eshera Cave) ( Figs 1 View FIGURE 1 , 2 View FIGURE 2 ). The air temperature at the sampling site was 10.2 °C, while the water temperature was 11.0 °C. Among the ten morphospecies of Collembola found in the cave, no specimens of A. colchicus sp. nov. were captured in the terrestrial habitat or by Barber traps.

Etymology. The species name “ colchicus ” is the Latinized adjective derived from Colchis (Colchida), historical name which in modern-day is western Georgia, the place where the type locality is situated. Colchis is known in Greek mythology as the land of the Golden Fleece, sought by Jason and the Argonauts.

Taxonomic remarks. The new species belongs to the A. caecus species group s. str. with 3, 2, 1, 1, 1 setae on the anterior side of the dens. It resembles two highly troglomorphic Caucasian species with extremely elongated claws— A. macronyx from Anukhvinskaya Cave (Anukhva Cave) and A. profundus from the Snezhnaya Cave System. Apart from elongated claws, all these species share the following characteristics: absence of spine-like setae on the head dorsum; very small or undetectable eyes; relatively long antennae (2× the head length) with 6–7 subsegments on Ant IV, with several annuli between neighboring subsegments; an enlarged antennal III organ; short empodia not reaching the tip of the much elongated corresponding claw; long posterior setae of the great abdomen (3–4× longer than the anterior setae); absence of distinctly spine-like setae on dens; mucro with partly or entirely accreted teeth on the lateral lamellae, a large anterior lamella, and with a not broadened tip. This set of important taxonomic features suggests a very close relationship among the considered taxa. From both mentioned species A. colchicus sp. nov. differs by presence of 3 axial setae on head dorsum (vs. 4), 7 setae on Ant I segment (vs. 6), absence of corner tooth on empodium of hind leg (vs. present), presence of ms5 seta on dorsal valve of Abd VI (vs. absent) and absence of mpi2 seta on lateral valve (vs. present). A combination of several characters allows distinguishing these three taxa as distinct separate species ( Table 3 View TABLE 3 ).