Hypogastrura metegensis Antipova & Babenko 2024, sp. nov.

Hypogastrura metegensis sp. nov.

Figs 1–13

Type material. Holotype female, North Caucasus, Kabardino-Balkaria, Psygansu River valley, southern spurs of Metegen Mt [43.1°N 43.5278°E], 2300 m alt., sedge bog, 19.09.2019. O. Makarova leg. Deposited in MSPU.

Paratypes, 2 males and 4 females, same habitat as holotype; 1 male and 1 female, same area, altitude and date, mosses with Dryas sp. All O. Makarova leg. Deposited in MSPU collection.

Diagnosis. A species of the monticola -group which differs from other members of the group by the following combination of characters: moderate dorsal and fine dental granulation,Ant. IV with three dorsal and two dorsolateral sensilla, Th. II–III with setae m6 present, tibiotarsal tenent setae blunt or slightly clavate, dens to mucro ratio as 2.2–3.2, and mucro with a low outer lamella reaching the apex.

Description. Body length discarding antennae 0.9–1.2 mm, holotype — 1.1 mm, sizes of males and females barely varying. Habitus typical of the genus. Body color in alcohol brownish of variable intensity, ventral side slightly paler, especially in furcal area (Fig. 1). Integument granulation moderate, usually with 6–8 granules between setae p1 on Abd. V.

Antennae almost equal in length to head.Ant. IV with a simple apical bulb (Fig. 9), sensilla (three dorsal, S1, S2, and S3 and two lateral, S7 and S8) cylindrical, elongate and slightly curved, well differentiated from common setae (Fig. 8); subapical organite (or) and microsensillum (ms) present, as usual. Ant. III with a typical AO, composed of two short, inner, club-like sensilla, two guard sensilla and one ms on outer side (Fig. 8). Ant. I–II with seven and 13 smooth common setae, respectively.

Head with 8+8 subequal eyes. PAO 1.5–2 times as large as adjacent ocellus, consisting of two elongated anterior and two rounded posterior lobes, an accessory boss present (Fig. 5). Distal edge of labrum with six low papillae, setal formula: 4/554. Labial palp with a full set of papillae (A–E), 14 guards (among them a1, b1, b2, d2, and e2 shorter and set on low papillae) and six proximal setae, a lateral process (lp) rudimentary. Basomedial field on labium (submentum) with four setae, basolateral field (mentum) with five setae, as usual. Head with 3+3 postlabial setae along ventral line. Maxillary head of the tullbergi - type, with three teeth on main part and six usual lamellae (Fig. 6): L.1 not extending beyond tip of maxillary teeth, L.2 and L.3 with short marginal filaments, all other lamellae beset with fine denticles. Outer maxillary lobe simple, with two sublobal hairs, as is usual for the genus.

Chaetotaxy of head typical of the genus, with 2+2 v-setae (Fig. 4). Most dorsal setae on body short and smooth, longer and slightly serrate on last abdominal segments. Sensorial setae 1.5–2.0 times as long as common ones. Main characteristics of tergal chaetotaxy: setae m6 always present on both Th. II and Th. III, setae m2 on Th. II, and m4 on Th. II–III present or absent (Fig. 3), often asymmetrical. Setae m2 and m3 on Th. III replaced by a single seta (m2/ 3 in Fig. 3) in intermediate position. Chaetotaxy of Abd. IV–V unstable, usually with few additional setae variable in number and position.

Chaetotaxy of legs 1–3 as follows: upper subcoxae—1, 2, 3 (among them, one macroseta on each subcoxa); lower subcoxae—0, 3, 3; coxae—(2)3, 3, 3; trochanters—7(8), 7(8), 7; femora—13–14, 13–14, 12–14; tibiotarsi— 19, 19, 18 setae, respectively. Tibiotarsal tenent setae (1–1–1) blunt or weakly clavate, about as long as 1.1–1.5 inner unguis edge (Fig. 13). Unguis with a small tooth in midsection of inner edge, lateral teeth invisible. Unguiculus slightly exceeding the middle of unguis inner edge, with a clear basal lamella.

Ventral tube with 4+4 distal setae. Retinaculum with 4+4 teeth (Fig. 12). Furca well-developed. Dorsal side of dens with fine granulation and seven smooth setae; outer basal seta as long as 2/3 dens (Fig. 10). Mucro elongate, approximately 0.3–0.4 as long as dens, its outer and inner lamellae low and fused to each other at some distance from mucro apex, forming a subapical tooth (Fig. 11).

Abdominal tip with small, slightly curved, anal spines on papillae adjacent to each other. The spines almost equal in length to basal papillae (Fig. 7).

Etymology. Named after Mount Metegen in the Rocky Ridge of the Greater Caucasus (Fig. 2), its foot being the type locality of the new species.

Affinities. Hypogastrura metegensis sp. nov. represents the monticola –group characterized by thin and long sensilla on Ant. IV; PAO 1.5–2 times as long as adjacent ocellus; labrum with clear distal papillae; unguiculus with a broad basal lamella; not more than 1–1–1 clavate tibiotarsal tenent setae; VT with 4+4(5) setae; retinaculum with 4+4 teeth; dens with seven setae, but without spine-like granules; Th. II–III usually with setae m6; some m-setae may also be present on Abd. V (Skarżyński 2009).

Until now, only one species of this group have been known in the entire Caucasus (Teberda, Western Caucasus): H. hatiparae. Six paratypes of this species, kept in the MSPU collection, have been rechecked. The species is really very similar to H. metegensis sp. nov. in having an almost identical dorsal chaetotaxy with setae m6 on Th. II–III and a slightly polychaetotic abdominal tip, as well as a relatively long mucro with low lateral lamellae. Nevertheless, it can be easily distinguished from H. metegensis sp. nov. due to the coarse granulation of the cuticle, the miniature anal spines on hardly distinguishable papillae, and the presence of six rather than five sensilla on Ant. IV, all being typical of H. metegensis sp. nov. The new species shares the absence of lateral sensillum S9 on Ant. IV with only four species of the group: H. monticola Stach, 1946, which is widespread in European mountains, being known from the French part of the Pyrenees, the Alps, the Tatras, the Carpathians and Sudetenland (Skarżyński 2009), and three Spanish, probably endemic species: H. hispanica (Steiner, 1955), H. dasiensis Selga, 1966 and H. herrerosvelai Arbea & Pérez Fernández, 2020 (see Table).

Hypogastrura metegensis sp. nov. and H. monticola show many characters in common, but the former differs in having a clearly longer mucro with lower lateral lamellae (dens/mucro ratio as 4–5 in H. monticola, vs 2.2–3.2 in H. metegensis sp. nov.). Apart from this, H. monticola is characterized by a finer cuticular granulation (13–16 granules between setae p1 on Abd. V, based on material from the Tatras, leg. A. Smolis, 1999, vs 6–8 such granules in H. metegensis sp. nov.), the pointed tenent setae on the tibiotarsi (blunt or slightly clavate in H. metegensis sp. nov.), and the presence of many additional m-setae on Abd. IV, vs only few such setae occasionally and usually asymmetrical present in H. metegensis sp. nov.

Hypogastrura hispanica was originally described as a member of the genus Ceratophysella, likely due to the special structure of the mucro: hook-shaped with a slightly rounded, tooth-like outer lamella. Apart from the mucro, H. hispanica also differs from H. metegensis sp. nov. in having 5+5 setae on VT, vs always 4+4 setae.

The most apparent feature clearly distinguishing H. metegensis sp. nov. from H. herrerosvelai, the latter species recently described from a Spanish cave, is the presence of setae m6 on thoracic terga II and III. In H. herrerosvelai, these setae are absent from Th. II and only occasionally present on Th. III, vs always present on both terga in H. metegensis sp. nov. The relatively short mucro (1/4–1/5 dens) with a rather high outer lamella may also be useful for separating these species. Comparing the chaetotaxy of the monticola -group members in the original description of H. herrerosvelai, Arbea & Pérez Fernández (2020, table 1) paid special attention to the number of m-setae on Abd. IV–V and of p-setae between sensilla on Abd. V. Unfortunately, both characters are highly variable in H. metegensis sp. nov. and most likely cannot be considered as reliable diagnostic features.

* based on Skarżyński (2009) and Arbea & Pérez Fernández (2020)

** According to Arbea & Pérez Fernández (2020), H. papillata sensu Jordana et al. 1997, described on the material from Portugal, lacks m6 setae on both Th. II–III. It can be supposed that this is a different, not yet described species.

Hypogastrura dasiensis, considered endemic to the Spanish Pyrenees, is perhaps the most similar to the new species. It also has three dorsal and two lateral sensilla on antennal segment IV, a similar dorsal chaetotaxy, distinctly clavate tenent setae on the tibiotarsi, and 4+4 distal setae on the VT. However, H. dasiensis is characterized by a coarse granulation of the integument, as well as the different shape and relative size of the mucro. The latter is probably the most reliable diagnostic feature to separate these two species. H. dasiensis has a shorter mucro: 1/4 as long as dens, according to the original description, 1/3 dens, according to Jordana et al. (1997) and, as a result, 1/3– 1/4 dens in Arbea & Pérez Fernández (2020). Besides this, as in most species of the group, the mucro of H. dasiensis has a wide outer lamella which is sharply narrowed before reaching the apex. As a result, a notch-like excavation (una excavación a modo de escotadura sensu Selga 1966, p. 147) is formed in front of the tip (see also Jordana et al. 1997, fig. 27Е). On the contrary, in H. metegensis sp. nov. the outer lamella is low, is gradually attenuated towards the tip and is merged with the inner one at some distance from the apex forming a subapical tooth.