Hypogastrura crinigera, Antipova, 2025

Antipova, M. D., 2025, A new species of the springtail genus Hypogastrura (Collembola: Hypogastruridae) from southern Kazakhstan, Middle Asia, Russian Entomological Journal 34 (1), pp. 1-9 : 2-8

Hypogastrura crinigera sp.n.

Figs 1–20 .

TYPE MATERIAL: Holotype female, Kazakhstan, Turkistan Region , East Kyzylkum sandy desert, basin of Syr Darya River, 85 km W of Arys, 42.2325 oN 67.8128 oE, 230 m alt., pitfall-traps, 14–16 October 2023, L. Kim leg. Deposited in MSPU.

Paratypes, 11 female, 11 males on slides, 8 slides with head parts, same data and deposition . 1 female, 3 males and 1 slide with mouthparts kept in the author’s collection.

OTHER MATERIAL: ca 100 specimens in alcohol from other 8 places located from 200 meters to 7 kilometers from the type locality.

DIAGNOSIS. A species of the manubrialis -group that differs from other members of the group by the following characters: the long, thick and strongly serrate setae covering the whole body, including a few basal antennomeres; the quite large anal spines; only four clearly differentiated sensilla on Ant. IV; the characteristic maxillary head with a short L.1 with a slightly broadened tip covered with two rows of filaments (apical and subapical), and several stiff spines in addition to small denticles at the base; and some peculiarities of chaetotaxy, for instance, the absence of setae m2 from both Th. II–III and of an m-row on Abd. V.

DESCRIPTION. Body length of holotype discarding antennae — 1.5 mm, sizes of males and females barely varying: female — 1.3 (1.09–1.61) mm, male — 1.16 (1.00–1.26) mm. Habitus typical of the genus. Body colour in alcohol dark blue ( Fig. 2 ), ventral side slightly paler, especially in furcal area ( Fig. 3 ). Integument granulation moderate to quite coarse, usually with 5–9 conical granules between setae p1 on Abd. V.

Antennae subequal in length to head. Ant. IV usually with a simple apical bulb ( Figs 7 , 16 ), sometimes with an outgrowth ( Fig. 17 ); common setae smooth or slightly jagged, sensilla (three on outer lateral side, S7, S8, S9 and one dorsal, S?) cylindrical, elongate and more strongly curved than common setae ( Figs 7–8 ), seta i not identified; subapical organite (or) and microsensillum (ms) present, as usual. Ant. III with a typical AO, composed of two short, inner, roundish sensilla, two elongated guard sensilla and one ms on outer side, common setae on Ant. III usually serrate ( Figs 7–8 ). Ant. I–II with 7 (seta p’ absent) and 13 serrate setae, respectively, those on ventral side somewhat more smooth.

Head with 8+8 subequal eyes. PAO 1–1.3 as long as adjacent ocellus, consisting of four bean-shaped lobes subequal in size, sometimes with minor outgrowths, an accessory boss invisible ( Fig. 19 ). Papillae on distal edge of labrum hardly expressed ( Fig. 20 ), setal formula: 4/554. Labial palp with a full set of papillae (A–E), 14 usual guards (among them a1, b1, b2, d2, and e2 shorter and borne by low papillae) and six proximal setae, a lateral process (lp) invisible. 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 with three teeth on main part and six lamellae ( Figs 6 , 18 ): L.1 not extending past tip of maxillary teeth, barely broadened, with an apical and a subapical row of filaments, also with a few bristles in basal part; 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 typical of the genus.

Head chaetotaxy typical, with 2+2 v-setae ( Fig. 13 ). Dorsal setae on head and body poorly differentiated, long, thick and distinctly serrate, on last abdominal segments slightly longer ( Fig. 4 ). Sensorial setae well-discernible, smooth, twice as thin and 0.2–0.8 times as long as common ones ( Fig. 5 ). Tergal chaetotaxy complete and typical of the group, with p4 and m7 on Th. II–III, p5 on Abd. I–IV and p3 on Abd. V being sensorial setae. The only notable characters are the absence of setae m2 from Th. II and of an m-row from Abd. V ( Figs 13–15 ).

Chaetotaxy of legs 1–3 as follows: upper subcoxae — 1, 2, 3 (all macrosetae); lower subcoxae — 0, 3, 3 (one macroseta, two microsetae); coxae — 3, 7(8), 6(7); trochanters — 7, 7, 7; femora — 13, 13, 12; tibiotarsi — 19, 19, 18 setae, respectively. Tibiotarsal tenent setae (1–1–1) weakly clavate, about as long as 1.2–1.4 inner unguis edge ( Fig. 11 ). Unguis with a clear inner tooth slightly shifted towards apical part, lateral teeth invisible. Unguiculus slightly exceeding the middle of unguis inner edge, basal lamella narrow ( Fig. 11 ).

Ventral tube with 4+4 distal setae. Retinaculum with 4+4 teeth. Furca well-developed. Dorsal side of dens with roundish coarse granulations and seven mostly smooth setae (sometimes bearing a few serrations visible under high magnification); outer basal seta as long as 0.6 dens ( Fig. 9 ). Mucro approximately 0.3–0.4 as long as dens, curved ventrally to varying degrees. Outer lamella rather high, with a subapical excavation in lateral view ( Fig. 10 ).

Abdominal tip with high, clearly defined papillae bearing the anal spines. Spines rather variable in length: from equal to papillae to 2 times larger ( Fig. 12 ). Inner edge of unguis to anal spines length ratio as 1: 0.60–0.86.

VARIABILITY. The following aberrations have been revealed in the type material: three anal spines on Abd. VI, absence of PAO from one of the sides of the head, asymmetric absence of m4 on Th. II, and split tergal setae .

NAME DERIVATION. The species is named for its unusually long dorsal setae. The epithet “ crinigera ” is the feminine singular of the Latin adjective “ criniger ” (meaning “having long hair”).

DISTRIBUTION AND ECOLOGY. Known only from the type locality: East Kyzylkum sandy desert, Kazakhstan .

AFFINITIES. The most noticeable distinguishing feature of H. crinigera sp.n. is undoubtedly its dorsal chaetom formed by long, thickened and strongly serrate setae, which taper only slightly towards their tips. Nothing similar is known for the described species of the genus. Hardly surprisingly, during the initial sorting the material it was considered a representative of the genus Ceratophysella Börner, 1932 rather than Hypogastrura . However, in fact it turned out to be a fairly typical species of the manubrialis -group, characterized by all usual features of the group: maxillary head with a modified L.1; weakly distinguished sensilla on Ant. IV; labrum without or with unclear distal papillae; unguiculus with a narrow basal lamella; not more than 1–1–1 tibiotarsal tenent setae; VT with 4+4 setae; retinaculum with 3+3 or 4+4 teeth; dens with seven setae, and comparatively coarse granulations on dens and body [ Yosii, 1960; Christiansen, Bellinger, 1980; Babenko et al., 1994; Skarżyński, 2009].

According to Bellinger et al. [1996 –2024], the manubrialis- group is currently represented by 28 named species. Hypogastrura crinigera sp.n. shows notable differences from all known species within the group, characterized, as it was mentioned above, by the presence of unusually thick, long and strongly serrate setae that cover the entire body, extending from the antennae to the furca. Clearly serrate setae have been documented only in a few species of the group, for instance, H. serrata (Ågren, 1904) (Scandinavia), H. pityusica Ellis, 1974 (Mediterranean) and H. tianshanica (Tien Shan) , but the degree of seta modifications in these species is hardly comparable with that of H. crinigera sp.n. Apart from this, all above species are clearly distinguishable from the new one by a number of other characters described below (see also Suppl. Table).

The chaetom in some representatives of the genus Hypogastrura is well known to be able of variation as a result of ecomorphosis associated with adaptations to a changing environment [ Cassagnau 1955, 1956a, b; Bonfanti, 2023]. Our material was collected during only one season (autumn) and it is probably impossible to exclude a potential connection between the structure of the setae and their seasonal modification under the influence of external conditions, given the arid habitat so very atypical of the taxon. However, the combination of a number of other subtle morphological features still does not allow us to relate H. crinigera sp.n. to any of the already known species.

Up to now only one congener, H. deserti Babenko, 1994 , appears to be known from comparable arid habitats (wormwood desert, Uzbekistan and the bank of a salty lake, Novosibirsk Region, Russia). This species shows a number of unique morphological characters easily distinguishing it from H. crinigera sp.n.: ventral setae on Th. II–III (absent from H. crinigera sp.n. as in all other known species of the genus), the absence of sublobal hairs (present in H. crinigera sp.n. as in the majority of other congeners), peculiar chaetotaxy of labrum (2/454, vs 4/ 554 in H. crinigera sp.n.), slightly reduced dorsal chaetotaxy, retinaculum with 3+3 teeth (vs 4+4 teeth in H. crinigera sp.n.), the absence of inner teeth from the unguis, different shape of mucro, fine cuticular granulations etc.

Hypogastrura crinigera sp.n. is significantly more similar to H. tianshanica , a species described from Issyk-Kul Region of Kirgizia and from a comparable habitat (dry riverbed, litter un- der Perowskia ) located ~680 air-km east of the type locality of the new species. Hypogastrura tianshanica has similarly serrate dorsal setae, relatively long anal spines that are twice the size of papillae, and it is also characterized by the absence of p’-seta from Ant. I. However, it can be easily distinguished from H. crinigera sp.n. due to its distinctive pale coloration, the presence of setae m2 on Th. II and of m-setae on Abd. V, dorsal sensorial setae being distinctly longer than common setae, pointed tenent setae on the tibiotarsi, retinaculum with 3+3 teeth, a relatively shorter mucro and the shape of the maxillary head with a wide L.1 clearly protruding beyond the teeth.

The presence of serrate setae on the dorsal side of the body also brings the new species closer to the Holarctic H. serrata . Fjellberg [1998] synonymized this species with H. ripperi Gisin, 1952 , suggesting this serration could be related to infections by Sporozoa, which had been noted during the species redescription by Ellis [1974]. Even without taking this into account, H. serrata differs from H. crinigera sp.n. quite significantly, primarily in having the tullbergi - type of the maxillary head and the distinctly pointed tenent setae on the tibiotarsi. Two more species, H. tigridis (Brown, 1926) ( Iraq) and H. pityusica , (Mediterranean) also show ciliate dorsal setae, yet both are distinguished by having 6 instead of 7 setae on the dens.

Despite the rather incompletely studied springtail fauna of Middle Asia, a fairly large number of other species of the manubrialis -group have also been recorded from the region and adjacent territories. Among them, there are not only such widespread species as H. assimilis (Krausbauer, 1898) , H. vernalis (Carl, 1901) and H. manubrialis (Tullberg, 1869) , but also those known only from a limited number of habitats, in particular H. yosii Stach, 1964 ( China and Russian Far East), H. rangkuli (Pamir, and also Taimyr, Alaska & India), H. turkmenica Babenko, 1994 (Turkmenia), H. druki Babenko, 1994 ( Mongolia) and H. ubsunurensis Babenko, 1999 (Siberia).

Only three of the above widespread species, i.e. H. assimilis , H. vernalis and H. manubrialis , apart from the shape of the setae, differ from H. crinigera sp.n. in the length of L. 1 in the maxillary head and in more than five (often up to 10) sensilla on Ant IV. Other distinguishing features are presented in Table.

Hypogastrura rangkuli was originally described from the Pamir region, located approximately 500 air-km southeast of the type locality of the newly described species. The most apparent distinguishing features are the tullbergi - type of the maxillary head [according to Fjellberg, 1984] and the increased number of sensilla on Ant. IV (up to 10, vs only 4 in H. crinigera sp.n.). Hypogastrura turkmenica (~1000 air-km southwest of the type locality of H. crinigera sp.n.) also differs in the peculiar structure of the maxillary capitulum [ Babenko et al., 1994: 53] and by the presence of m-setae on Abd. V and seven sensilla on Ant. IV.

The other two Asian species, H. yosii and H. druki , both of which share with H. crinigera sp.n. coarse granulations on the cuticle and the number of teeth on the retinaculum (4+4). In addition, the former also lacks m2 setae on Th. II and setae of m-row on Abd. V, and it has weakly clavate tenent setae. Hypogastrura yosii may be distinguished from H. crinigera sp.n. by an increased number of sensilla on Ant. IV (9–10, vs 4 in H. crinigera sp.n.), rather large PAO (1.5–2.5, vs 1.0–1.3 times as large as adjacent ocellus in H. crinigera sp.n.), structure of the mucro, the shape of the maxillary head, and the absence of small labial guard a1 (see Babenko et al. [2020]) (present in H. crinigera sp.n.). Hypogastrura druki is also very different from H. crinigera sp.n. in having both setae m2 on Th. II and m-setae on Abd. V, as well as pointed tibiotarsal setae and long maxillary L.1.

The most characteristic feature of H. ubsunurensis , which makes it distinguished from H. crinigera sp.n., is the presence of only 3+3 teeth on the retinaculum, this being not very common in the group, yet observed, for example, in H. gisini Strenzke 1954 , H. breviempodialis ( Stach, 1949) , H. tianshanica and H. cretensis Skarżyński et Gwiazdowicz 2022 . Apart from this, the dorsal setae of H. ubsunurensis are short and thin, only slightly thickened at the end of the abdomen, and L.1 on the maxillary head is strongly elongated and broadened at the apex.

Supplementary data. The following materials are available online.

Supplementary Table. Main morphological differences between the most similar members of the manubrialis -group of the genus Hypogastrura and H. crinigera sp.n.

Acknowledgments. I would like to express my sincere thanks to Leonid Kim (The Institute of Zoology, Almaty) for collecting the specimens of the new species and to Anna Nekhaeva (A.N. Severtsov Institute of Ecology & Evolution, Moscow), who transferred it to me. I am deeply indebted to my supervisor, Anatoly Babenko, for inspiring me and providing assistance throughout the implementation of this work. I would also like to express my gratitude to Sergei Golovatch for editing the English, to reviewer, as well as to the editor for their valuable suggestions to improve the manuscript.

Figures

Fig. 1–3. Hypogastrura crinigera sp.n.: 1 — the type locality; 2, 3 — H. crinigera sp.n., non-type, in alcohol, dorsal and lateral views, respectively. Рис. 1–3. Hypogastrura crinigera sp.n.: 1 — типовое местообитание; 2, 3 — H. crinigera sp.n., нетиповой обраЗец, в спирте, дорсальный и латеральный виды, соответственно.

Fig. 4–8. Hypogastrura crinigera sp.n.: 4 — common seta of Abd. II; 5 — sensilla of Th. II; 6 — maxillary head; 7 — chaetotaxy of Ant. III–IV (dorsal side); 8 — chaetotaxy of Ant. III–IV (outer lateral side). Scales: 0.1 mm (4, 5, 7, 8) and 0.01 mm (6). Рис. 4–8. Hypogastrura crinigera sp.n.: 4 — обычнаЯ хета Abd. II; 5 — сенсилла Th. II; 6 — максиллЯрнаЯ головка; 7 — хетотаксиЯ Ant. III–IV (дорсальнаЯ сторона); 8 — хетотаксиЯ Ant. III–IV (внешнЯЯ латеральнаЯ сторона). Масштаб: 0,1 мм (4, 5, 7, 8) и 0,01 мм (6).

Fig. 9–12. Hypogastrura crinigera sp.n.: 9 — dorsal view of furca; 10 — lateral view of furca; 11 — claw and tibiotarsus with tenent seta; 12 — tip of Abd. VI with anal spines (lateral view). Scale: 0.1 mm. Рис. 9–12. Hypogastrura crinigera sp.n.: 9 — дорсальнаЯ сторона фурки; 10 — латеральнаЯ сторона фурки; 11 — коготок и тибиотарЗус с головчатой хетой; 12 — анальные шипы на конце Abd. VI (вид сбоку). Масштаб: 0,1 мм.

Fig. 13–15. Hypogastrura crinigera sp.n.: 13 — dorsal general view and chaetotaxy; 14 — dorsal chaetotaxy of Th. II; 15 — dorsal chaetotaxy of Abd. IV. Scale: 1 mm (13), 0.1 mm (14–15). Рис. 13–15. Hypogastrura crinigera sp.n.: 13 — обЩий дорсальный вид и хетотаксиЯ; 14 — дорсальнаЯ хетотаксиЯ Th. II; 15 — дорсальнаЯ хетотаксиЯ Abd. IV. Масштаб: 1 мм (13), 0,1 мм (14–15).

Fig. 16–20. Hypogastrura crinigera sp.n.: 16 — Ant. IV with a simple apical bulb; 17 — finger–like outgrowth on the apical bulb of Ant IV; 18 — Maxillary head; 19 — PAO and nearest ocelli; 20 — Labral edge. Рис. 16–20. Hypogastrura crinigera sp.n.: 16 — апикальнаЯ папилла Ant. IV; 17 — пальцевидный вырост апикальной папиллы Ant. IV; 18 — головка максиллы; 19 — ПАО и окруЖаюЩие глаЗки; 20 — край верхней губы.