Oligaphorura interrupta (Fjellberg, 1987) Fjellberg, 1987

Babenko, Anatoly B. & Fjellberg, Arne, 2015, Subdivision of the tribe Oligaphorurini in the light of new and lesser known species from North-East Russia (Collembola, Onychiuridae, Onychiurinae), ZooKeys 488, pp. 47-75 : 54-55

Taxon classification Animalia Collembola Onychiuridae

Oligaphorura interrupta (Fjellberg, 1987) comb. n.

Onychiurus (Archaphorura) interruptus Fjellberg, 1987: 282.

Micraphorura interrupta (Fjellberg): www.collembola.org

Material.

holotype, ♀, "USSR, Magadan Reg., "Death Valley", Magadan-Ust’ Umchug [road], 209 km from Magadan, moss, lichen, Vaccinium , 30 vii 1979" (CNC 165045, type No 20107); Paratypes, 9♀ and 1♂, same sample (CNC 165134, type No 20106), all A. Fjellberg leg.

Additional material.

1 specimen, Magadan District, Bolshoi Annachag Mts. Range, upper reaches of Kolyma River, field station “Aborigen” [61°56'N, 149°40'E], alpine study area (lichen, moss, Dryas , Empetrum ), 26 vii 1979, V. Behan leg.; 11 specimens, same region, Butugychag ("Death Valley") [61°18'N, 149°11'E], moist Sphagnum , litter Betula nana , Alnus thickets, 30 vii 1979, A. Fjellberg leg.; 10 specimens, Magadan vicinities, "Snow Valley", rich meadow ( Veratrum , Angelica ), 20 viii 1979; ca. 15 specimens, Northern Yakutia, Shirokostan Peninsula, Ledyanoe lake [72°25'N, 141°00'E], various habitats, 1994, A. Babenko leg.; 1 ♀, North-Eastern Yakutia, delta of Indigirka river [71°26'N, 149°45'E], Eriophorum vaginatum tussock, 1994, A. Babenko leg.; ca. 30 specimens, Magadan District, upper reaches of Ola River [60°39'N, 151°16'E], various sites, viii 2011, A. Babenko leg.

Redescription.

Colour white. Size 0.75 mm. Body shape cylindrical. Antennae about as long as head, Ant.3-4 broad, club-like. Ant.4 with a peg-like subapical organite, microsensillum located in proximal row of setae. AO consisting of 5 long and thin papillae, two sensory rods, two granulated sensory clubs (internal straight, external much bigger and bent), 5 guard setae and a lateral microsensillum set below the organ. Ant.1 and 2 with 8 setae and 13-14 setae respectively. PAO with 3-4 lobes, longer than nearest pseudocellus. Labrum with 4/3-2-2 setae. Apical part of labium with thick terminal setae on papillae A and C, common number of guard setae (6 long and 4 spiniform ones), and 6 proximal setae. Basal fields with 4+5(6) setae. Maxillary palp simple with two sublobal hairs.

Most common dorsal pseudocellar formula (pso) as 32/033/33353, submedial pso a and b on Abd.1-2 set close together (with pso b on level with setae p3). Variations are frequent and specimens with additional pso on some abdominal terga (usually asymmetrical) are seen. The whole formula may be expressed as follows, 32/033/3(4),3(4),3(4),(4)5,3(4). Ventral side of head with two pso as usual. Parapseudocelli (psx) invisible. Each subcoxa with one pso. Granulation fine and uniform, sometimes clearly coarser around pseudocelli. Dorsal chaetotaxy almost symmetrical, setae smooth, macrosetae short, needle-like usually blunt at tip, sensory setae more or less distinct, usually 2/011/22211 in number, sensilla like, broaden seta usually present on lower Scx.3. Th.1 with 5-6 setae on each side. Both Th.2 and 3 with lateral ms, p1 on head and Th.2-3 usually slightly in front of p2, Abd.1-3 with setae p4 usually present. Abd.5 with m1 curved, thinner and shorter than the straight a1 and p1. Unpaired setae: d0 absent, p0 frequently present on Abd.5, Abd.6 with two axial setae, a0 clearly shorter than a2. Thoracic sterna 1-3 with 0-0-1 setae, sometimes setae completely absent. Furca remnant as a small fold in some distance from anterior border of Abd.4 sternum, chaetotaxy of manubrial field in juveniles as in Fig. 19, usually with 3+3 proximal q- setae and 3+3 setae in triangles between cuticular fold and q- setae. In adults 1-3 additional setae usually present in intermediate position (Fig. 20). Four irregular setal rows may be distinguished. Ventral tube with 6+6(7) distal and 2(1) proximal setae at base. Subcoxae usually with 3(4)-4(5)-4 setae, tibiotarsi with 20-20-19 setae: each distal whorl (A+T) with 11 setae, whorl B with 7-7-6 setae, setae M and Y present on all tibiotarsi. Unguis simple, without inner or lateral teeth, unguiculus with small basal lamella, about 3/4 as long as unguis. Anal spines short and thick, slightly bent and constricted at base, set without papillae.

Remarks.

The number of pseudocelli in the species appears to be more variable than stated in the original description by Fjellberg (1987), even within the region of the type locality. That is why Nearctic Oligaphorura nuda , characterized by increased number of abdominal pso, appears to be hardly separable from Oligaphorura interrupta despite their different generic positions on the www.collembola.org. Nevertheless the chaetotaxy of manubrial field in Oligaphorura interrupta is identical to that of Oligaphorura groenlandica (cf. Figs 17-18 and Figs 19-20) and clearly differs from the pattern typical of Micraphorura absoloni (Figs 26-27). The structure of manubrial field in the nuda holotype (CNC 165047, type No 20103) also indicates its position within the genus Oligaphorura .

The presence of ventral setae on Th.3 in Oligaphorura interrupta was used by Fjellberg (1987) as an additional diagnostic character to separate Oligaphorura interrupta and Oligaphorura nuda (setae absent). However, new material of Oligaphorura interrupta from various regions of eastern Palaearctic shows this character to be invalid. Some specimens of Oligaphorura interrupta may also be completely devoid of ventral setae on thorax. More material is evidently needed to clarify the real relationships between these two species.

Only one other known species of the tribe shares the absence of pso on Th.1 combined with presence of 5 pso on Abd.4 with Oligaphorura interrupta and Oligaphorura nuda : Oligaphorura reversa (Fjellberg, 1987). This characteristic species differs from the above-mentioned species in having an unusual position of the dorsal pseudocelli on Abd.1-3: the medial pso a is set in a posterior position, clearly behind submedial pso b.

The species listed as Oligaphorura sp. aff. nuda in Babenko (2013) from Taimyr is another congener with a similar dorsal pseudocellar formula. It differs from both Oligaphorura interrupta and Oligaphorura nuda having 1+1 ventral pso on Abd.4.