Hypogastrura exigua Gisin, 1958

Skarżyński, Dariusz, 2011, A taxonomic study on some Alpine Hypogastrura Bourlet, 1839 (Collembola, Hypogastruridae), Zootaxa 2786, pp. 62-68 : 63-65

Hypogastrura exigua Gisin, 1958

Figs 2–8

Material examined. Holotype, female on slide, Ma3a, Italy, Dolomites, Padon, N Marmolada, 2,300–2,500m a.s.l., leg. Marcuzzi. Paratypes: 1 male, 8 juveniles, same data as holotype ( MNHG).

Other material. Italy (Dolomites, Marmolada): 1 female, Ma9c, 2,200m a.s.l., alpine grassland, leg. Marcuzzi ( MNHG); 1 female and 1 male, Ma19a, 2,600m a.s.l., pioneer saxifrages and Arabis sp., leg. Marcuzzi ( MNHG); 53 ex., mosses on rocks below pass Forcella de la Marmolada, 2,500–2,800m a.s.l., viii.2009, collector unknown ( DBET); Austria (other material of H. parvula from Hohe Tauern, Glockner group cited in Haybach (1972): 11 ex., G 606 (nr. 1), Wasserfallwinkel, foreground of Wasserfallkeeses, 2,640m a.s.l., zone of Saxifraga oppositifolia , tussock of Saxifraga with Bryum cf. pallescens , 7.vii.1967, leg. H. Franz ( NHMV); 6 ex., Gl 9 (nr. 22), east slope of Gamsgrube, tussock of Salix serpyllifolia , Ranunculus glacialis , Sesleria sp., Poa alpina vivipara , 2,780m a.s.l., leg. G. Haybach ( MNHG).

Redescription. Body length up to 0.8 mm. Colour spotted grey-brown. Granulation fine and uniform, 6–8 granules between setae p1 on abd. V.

Chaetotaxy of head typical of the genus. Setae short and smooth. Body sensilla (s) 2–3 times longer than ordinary setae, fine and smooth. Dorsal chaetotaxy of th. II and abd. III–VI as in Figs. 2–3 . Th. I with 3 + 3 setae. Th. II with setae m2, m3 and m4. Th. III with setae m4 and sometimes m3. Setae p3 and p7 on abd. IV present. Abd. V with setae a 2 in backward position, setae p2 present and m-setae absent. Subcoxae I, II, III with 1, 2, 3 setae respectively. Microsensillum on thoracic tergum II present.

Ant. IV with simple apical vesicle, subapical organite (or), microsensillum (ms), 4 (1 dorsal and 3 lateral) curved, short, cylindrical sensilla ( Fig. 5 ). Ant. III-organ with two long (outer) and two short (internal) sensilla. Microsensillum on ant. III present ( Fig. 5 ). Ant. I with 7 setae (seta p’ absent).

Ocelli 8 + 8. Postantennal organ with 4 (rarely 5) lobes typical of the genus, about 1.5 times larger than neighbour ocellus ( Fig. 6 ). Accessory boss absent. Labrum with 4 apical papillae. Labral setae 5, 5, 4, prelabrals 4. Maxillary head and labium of the H. tullbergi type. Outer lobe of maxilla with 2 sublobal hairs.

Tibiotarsi I, II, III with 19, 19, 18 setae respectively. Apical seta A1 clavate. Claws with small inner tooth. Empodial appendage with broad basal lamella and apical filament reaching slightly beyond middle of inner lamella of unguis ( Fig. 7 ).

Ventral tube with 5 setae on each side (3 in upper and 2 in lower row) ( Fig. 4 ). Retinaculum with 3 + 3 teeth.

Furca slightly reduced (ratio dens + mucro/inner lamella of claws III c. 2). Dorsal side of dens with fine, uniform granulation and 3–5 (usually 4) setae. Mucro spine-like with indistinct, low outer lamella. Ratio dens/mucro 3–3.5 ( Fig. 8 ).

Anal spines small, situated on low basal papillae ( Fig. 3 ).

Remarks. According to Gisin (1958), H. exigua has a constant number (5) of setae on the dens. However, examination of the original material revealed the existence of some variability in this feature. The holotype has 4 + 5 setae on the dens, the paratype (male) and a female from the sample Ma 9c have 5 + 5, a female and a male from the sample Ma 19a have 4 + 5 and 4 + 4 respectively. Adults recently collected from the area of the type locality also show variable setae numbers: 1 ex. 3 + 3, 1 ex. 3 + 4, 6 ex. 4 + 4, 1 ex. 5 + 3, 4 ex. 5 + 4. In the light of such variability, individuals of H. parvula (cited as other material in Haybach 1972) with 3 + 4 (3 ex.), 4 + 4 (11 ex.) and 4 + 5 (1 ex.) setae on the dens and a set of characters identical to H. exigua must be considered conspecific with the latter species.

Affinities. H. exigua clearly differs from all Hypogastrura species mentioned in the introduction in having a larger number of setae on the ventral tube (5 + 5 versus 4 + 4). The low number of setae on the dens (3–5 usually 4) makes this species somewhat similar to H. oreophila (2–4 usually 3), H. magistri from Siberia (5) and H. mongolica from Mongolia (4). Nevertheless, the first two species have additional m-setae on abd. V, and H. magistri has plurichaetotic chaetotaxy of abd. IV and 6 cylindrical ant. IV sensilla.

A comparison with H. mongolica is impossible at present since the holotype (Dog-Cagan Nuur, Northern Mongolia, sample of humus taken in a forest on the western side of Lake Chavsgal Nuur, 3 km from the lake, 10.vii.1975, leg. Dr. Kiefer, MNHG), which was the only basis for the original description ( Nosek 1976), appeared to be juvenile without genital plate. Moreover, the quality of the type specimen is rather poor and numerous structures (e.g. antennal chaetotaxy) are weakly visible. The description remains in general accordance with the holotype, but the arrangement of body setae is erroneously represented. In reality, chaetotaxy is typical for Hypogastrura : th. I. with 3 + 3 setae, th. II with setae m2, m3 (m4?) and dorsal body sensilla in position p4, abd. I with setae m3, m4 and body sensilla in position p4, abd. V with setae p1 clearly shorter than body sensilla. H. mongolica should be redescribed using adult topotypes.

The remaining species, i.e. H. pizzoci , H. capitata ( Lebanon) , H. verruculata ( China) and H. ramia (S Korea), are easy to distinguish from H. exigua as they have 6 setae on the dens. H. exigua is also similar to one of the Orogastrura members; for more complete information see the remarks to O. parva .

Figures

FIGURES 1 – 8. O. parva: 1, postantennal organ and ocelli; H. exigua: 2, chaetotaxy of th. II; 3, chaetotaxy of abd. III – VI; 4, chaetotaxy of ventral tube; 5, chaetotaxy of ant. III – IV; 6, postantennal organ and ocelli; 7, claw III with empodial appendage; 8, furca. Abbreviations in text.