Xenylla aculeata, Babenko & Efeykin & Bizin, 2020

Babenko, Anatoly, Efeykin, Boris & Bizin, Mikhail, 2020, Three new and one little-known species of Hypogastruridae (Collembola) from Russia's northeast, ZooKeys 1005, pp. 1-20 : 1

Xenylla aculeata sp. nov. Figs 30-35

Type material.

Holotype Russia, North-East • ♂; Magadan Province, "Magadan-Ola Road (closer to Ola) [~ 59°35.25'N, 151°08.00'E]; treeless bog with Ledum , Arctostaphylos , Empetrum , and Betula vegetation (sample taken in Carex and moss), 20.07.1979"; V. Behan leg. The type is deposited in MSPU.

Diagnosis.

A species of chaetotaxic group VI (b) of the genus Xenylla Tullberg, 1869, characterised by the presence of one sublobal seta on the maxillary outer lobe and a complete reduction of both furca and retinaculum.

Description.

Holotype length 0.67 mm. Intravital colour unknown, holotype stored in alcohol for more than 30 years completely lacks dark pigment even on the eye fields. Tegument granulations rather fine and uniform. Ant.4 with a simple apical vesicle and four blunt sensilla (one dorsal and three lateral), rather short and subequal in size, both subapical microsensillum and organite invisible due to the poor condition of the slide. AO typical of the genus, outer sensilla rather short. Ant.1 and Ant.2 with seven and eleven setae, respectively.

Head with 5+5 subequal ocelli, as usual. Buccal cone typical of the genus, not elongate. Setal formula of labrum, 4/554, setae of distal row clearly thickened. Labium with all common papillae (A-E), 9 guards (five long and four short, truncate and papillate) and six proximal setae. Basomedial field of labium (submentum) with four setae, basolateral field (mentum) with five setae, as usual. Maxillary outer lobe simple, with one sublobal seta.

Most dorsal setae stout, finely ciliate and clearly differentiated into finer microsetae and subspiniform macrosetae, sensilla usually long and straight, especially on abdominal tip and laterally on Th.2 and Th.3 (Figs 30-31 ). Head with all usual dorsal setae present, except for c1 [b]; setae p1, p4, d2, oc2, q1, q3, l0, l1, and l3 more or less clear macrosetae, l1 only slightly longer than l3 (ratio = 1.1-1.2/1). Th.2 and Th.3 with seta a2 in a posterior position compared to a1 [h1], both p1 and p2 setae set in front of p3, setae la1 and m3 absent [i and k]; setae p1, p5 and p6 being macrosetae, lateral sensilla long, but dorsal ones rather short (Fig. 30 ). Chaetotaxy of abdominal terga as follows: Abd.1 without p5, m3 setae absent from Abd.4 [o] and a2 from Abd.5 [q] (Fig. 31 ). Ventral chaetotaxy: head with setae p1 and m3 (Fig. 32 ), Th.2 and Th. 3 with 1+1 axial setae, abdominal sterna as in Fig. 34 , Abd.2 with p1, but without p2, Abd.3 with a medial unpaired seta, Abd.4 with only one m-seta (m1 and m2 absent [a4 and a5]). General code of chaetom: bh1ikoqa4a5.

Ventral tube with 4+4 setae. furca and retinaculum completely absent. Tibiotarsi of legs 1-3 with 19, 19, and 18 setae, respectively; all setae of distal whorls (A+T) more or less clearly clavate (Figs 34 , 35 ). Anal spines rather long and set on subequal cuticular papillae (Fig. 31 ).

Etymology.

The name of the new species is derived from the Latin Xenylla aculeata , meaning spiny, to reflect the shape of the dorsal macrosetae characteristic of X. aculeata sp. nov.

Affinities.

The chaetotaxic pattern of X. aculeata sp. nov. allows us to include it into group VI (b), although a forward position of both p1 and p2 on Th. 2 and Th.3 appears to be unique to the new species. There is only one other species in the group that has neither a furca nor a retinaculum, viz. X. osetica Stebaeva & Potapov, 1994. Yet the latter species can easily be distinguished from X. aculeata sp. nov. by the presence of three sublobal setae on the maxillary outer lobe (vs. one in X. aculeata sp. nov.) and a complete chaetotaxy of Th.2 and Th.3 with setae al1 and m3 being present (absent in X. aculeata sp. nov.). Thus latter character (the absence of setae) seems to point to the relations between X. aculeata sp. nov. and several other congeners of the same group that share a functional furca with one ( X. betulae Fjellberg, 1985) or two dental setae ( X. corticalis Börner, 1901, X. grisea Axelson, 1900, X. hexagona Fjellberg, 1992, and X. laurisilvae Fjellberg, 1992). Among these species, only X. betulae has hitherto been known from the region under study. It appears to be rather similar to the new species in having an identical dorsal chaetotaxy including such fine characters as short sensilla in p-row on Th.2-Abd.1 and the usual absence of setae p5 from Abd.1 and of setae p7 from Abd.4. Ventral chaetotaxy (the absence of p2 from Abd.2 and of some m-setae from Abd.4, the presence of axial unpaired setae on Abd.3), the rather strong anal spines, and the long stout setae on the abdominal tip are also similar. Apart from the complete absence of a furca, X. aculeata sp. nov. differs from X. betulae in having much finer tegument granulation, coarser and more clearly differentiated dorsal setae, only one sublobal seta on the maxillary outer lobe (vs. two sublobals in X. betulae ), p1-setae in an anterior position on Th.2 and Th.3, and numerous clavate setae on tibiotarsi (vs. 2-2-2 in X. betulae ). The latter character appears to be unique in the genus, but needs verification based on fresh material.

Distribution and ecology.

The only known specimen of X. aculeata sp. nov. was found in a typical swampy association of the region, but a search in similar communities in the same area failed to reveal additional material. Taking this into account, as well as some morphological traits of the new species, namely the complete reduction of a furca and the presence of numerous clavate tibiotarsal setae, X. aculeata sp. nov. can be assumed to rather represent a corticicolous, not hygrophilous, species.

Figures

Figures 30 - 35. Xenylla aculeata sp. nov. 30 dorsal chaetotaxy of head and thorax 31 dorsal chaetotaxy of abdomen 32 ventral chaetotaxy of head 33 ventral chaetotaxy of Abd. 2 - 4 34, 35 tip of tibiotarsus, different views. Scale bars: 0.1 mm (30 - 33), 0.01 mm (34, 35).