Micranurida distincta, Babenko & Shveenkova & Potapov, 2022

Babenko, Anatoly, Shveenkova, Yulia & Potapov, Mikhail, 2022, The genus Micranurida Börner, 1901 sensu Deharveng 1982 (Collembola Neanuridae, Pseudachorutinae) in the fauna of the Russian Far East, Zootaxa 5188 (5), pp. 489-500 : 493-496

Micranurida distincta sp. nov.

Figs 12–23 ; Table 1

Type material. Holotype: female, Southern Primorye , Chuguev District , National Park «Zov Tigra», Mount Oblachnaya, Ussuri River valley, mixed forest, 43°36.04'N 134°11.58'E, ~ 550 m alt., rotten wood, 19–20 September 2018. A. Kuprin leg. Paratypes: 1 juvenile, same region, Partisan District , Mount Olkhovaya, mixed forest in valley, 43°18.35'N 133°40.07'E, ~ 500 m alt., litter, 20 August 2018. M. Potapov, Yu. Shveenkova & A. Kuprin leg. ; 1 immature female, same region, Ussuri State Nature Reserve , mixed forest, 43°38.2'N 132°20.98'E, ~ 380 m alt., litter, 23 July 2016. N. Kuznetsova & M. Potapov leg.

Diagnosis. A white, unpigmented species characterized by the absence of ocelli; the presence of six ovoid or flame-shaped sensilla, and the absence of seta i on Ant. IV; dorsal side of body with prominent fields of coarser granulation; the presence of only six setae on basal parts of labium; almost complete dorsal chaetotaxy with p2 present on all terga from Th. II to Abd. IV; thickened lateral sensilla on Th. II and tergum of Abd. IV, and 15–15–14 or 14–14–13 setae on the tibiotarsi.

Description. Length (without antennae) 0.36–0.38 mm, holotype – 0.38 mm. Habitus similar to the genus, slightly expanded. Body white, without pigment. Head and all terga with regular prominent fields of coarser granulation ( Fig. 15 ).

Antennae slightly shorter than head, Ant. III–IV fused dorsally. Ant. IV with simple apical vesicle and six more or less spherical or flame-shaped sensilla (S1–S4, S7–S8); external ms present as usual but subapical or and seta i absent ( Figs 16–17 ). Antennal organ of Ant. III typical, inner sensilla small, both sgv and sgd curved, rather small and subequal. Ant. I–II with 7 and 11 setae, respectively.

Ocelli absent. PAO rounded or slightly elliptic, consisting of 5–9 vesicles ( Figs 18–20 ). Buccal cone not especially long. Maxilla styliform, lamellae not seen. Mandible delicate, with at least three tiny apical teeth. Labrum with 7–10 (?) labral and four prelabral setae. Main part of labium with four ordinary setae A–D, sensorial elements absent; submentum and mentum with three setae each, probable homology as in Fig. 21 , i.e. setae E and e absent. Head ventrally with 2+2 postlabial setae as usual.

Dorsal chaetotaxy almost complete and symmetrical ( Fig. 12 ). Ordinary setae thin and acuminate, lateral sensilla on Th. II and dorsal one on Abd. IV clearly thickened, candle-like; other dorsal sensilla slender, thin and longer than ordinary setae, total number of tergal sensilla as usual: 22/11111; lateral ms present only on Th. II. Head with unpaired seta d0 and 3 setae on prominent ocular field ( Fig. 13 ). Th. I with 2+2 setae. All terga from Th. II to Abd. IV with setae p2 present and set anteriorly to setae p1 and p3. Abd. V with 1+1 axial setae (p1) between sensilla p3, i.e. setae a1 and p2 absent. Unlike the pattern of two axial fields of coarser granulation characteristic to all terga from Th. II to Abd. III, axial setae on Abd. IV (a1, p1 and p2) and Abd. V (p1 and p3) set on single medial field.

Thoracic sterna without setae. Ventral tube with 4+4 setae. The presence of unpaired axial setae on abdominal sterna uncertain: such seta present on sternum of Abd. III in one paratype, but two setae present on this position in holotype and another paratype ( Fig. 14 ). Furcal field without distinct cuticular swelling with few tiny setae in mid sternal position of Abd. IV. Anal valves with two hr setae each.

Legs I –III with 1, 2, 2 setae on upper subcoxae, 0,?,? setae on lower subcoxae, 3, 5, 6 setae on coxae, 5, 5, 5 on trochanters, and 12, 11, 10 setae on femora. Tibiotarsi with 15–15–14 setae, respectively, i.e. setae T2 , T3 , A4 and M absent , as well as seta B7 on leg III ( Figs 22–23 ), one of the paratypes additionally lacks seta A5, having totally 14–14–13 tibiotarsal setae. Unguis toothless, unguiculus absent as usual.

Remarks. The material from Anyuinski National Park, Khabarovsk Territory, contains one immature specimen which also lacks ocelli, has coarse granulation of the integument (but without prominent tubercles), six antennal sensilla, and strongly swollen sensilla on Th. II and Abd. IV. Unlike M. distincta sp. nov., it is characterized by the presence of seta i on Ant. IV, three ordinary setae and two sensory elements on the main part of the labium, more strongly reduced dorsal chaetotaxy without p2 setae on the abdominal terga, and a complete set of tibiotarsal setae, i.e. altogether 19–19–18, respectively. Obviously, this is a different species, probably related to M. spirillifera Hammer, 1953 , but additional material is necessary to describe it.

Etymology. The name of the new species reflects its clear differences from congeners, from Latin distinctus– – distinct.

Affinities. The genus Micranurida s. str. embodies only six species characterized by the presence of six sensilla (including sensillum S2 sensu D’Haese) on Ant. IV, namely, M. spirillifera , M. retezatica Gruia & Harșia, 1990 , M. bescidica Smolis & Skarżyński, 2004 , M. rostrata , M. russica and M. potapovi . Most of them are easily distinguished by the number of tibiotarsal setae: 15–15–14 setae in M. distincta sp. nov., vs 12–12– 11 in M. potapovi , 14– 13–14 in M. rostrata , 14–14– 14 in M. bescidica and 17–17– 16 in M. spirillifera and M. russica ( Table 1 ). This character is unknown only for M. retezatica , a European species characterized by elongated sensilla S7 on the antennae, as well as the absence of p2 setae on all terga.

The presence of clearly defined fields of coarser granulation on all terga makes it easy to distinguish M. distincta sp. nov. from the vast majority of congeners. Perhaps the only exception is M. russica , described from the same region (a comparison with the latter species is given below).

Taking into account the dorsal chaetotaxy of M. distincta sp. nov., in particular, the presence of p2 setae not only on the thoracic, but also on the abdominal terga, it is comparable only to three Eastern Palearctic species of the above list, namely, M. rostrata , M. potapovi , and M. russica . Of these, the former two are eyeless, like M. distincta sp. nov., while M. russica has 1+1 ocelli. However, it is the latter species, whose main diagnostic feature (the fusion of two sensilla on the antennae) is almost unique to the genus (a similar fusion is known only in M. bescidica ), that seems to be most close to M. distincta sp. nov. This assumption is mainly based on a high similarity of their dorsal chaetotaxy, in particular the anterior position of the p2 setae on the terga and the location of all dorsal setae within the fields of enlarged granules. The only sound difference between the dorsal chaetotaxy of these two species lies in the presence of four ordinary chaetae (а3, а4, m4 and p4) in dorsolateral position on Th. II-III in M. russica (vs three such setae in M. distincta sp. nov., i.e. m4 is absent), as well as 2+2 setae between sensilla on Abd. V in M. russica , vs 1+1 setae in M. distincta sp. nov.

It is also noteworthy that these two species are not only very similar morphologically and inhabit the same region, but both can also occur in the same biotopes and even in the same soil sample. Nevertheless, in addition to the above-mentioned differences in dorsal chaetotaxy, the number of tibiotarsal setae, and the presence/absence of ocelli, there are several other subtle, but significant differences that indicate the extent of possible variation in some morphological structures. Thus, the new species lacks seta i on Ant. IV, which is present in the majority of related species, including M. russica . The absence of this seta is known only in M. bescidica and M. rostrata . Some reduction of setae in the basal parts of the labium (mentum and submentum) also deserves mention. Nothing similar seems to have previously been noted in the genus.

Figures

FIGURES 12–14. Micranurida distincta sp. nov.: 12, dorsal chaetotaxy, Th. I–Abd. VI; 13, head chaetotaxy, dorsolateral view; 14, Abd. I–Abd. VI, ventrolateral view. Scales: 0.1 mm.

FIGURES 15–23. Micranurida distincta sp. nov.: 15, habitus; 16, Ant. III–IV (outer side); 17, ibid. (inner side); 18–20, PAO; 21, labium; 22, tibiotarsus of leg II (outer side); 23, ibid. (inner side). Scales. Fig 15: 0.1 mm; 16–23: 0.01 mm.