Oribatella arctica Thor, 1930

Behan-Pelletier, V. M., 2011, Oribatella (Acari, Oribatida, Oribatellidae) of eastern North America, Zootaxa 2973 (1), pp. 1-56 : 5

Oribatella arctica Thor, 1930

Oribatella arctica Thor, 1930, p. 97

( Fig. 1A–F )

Material examined. Svalbard, Adventsdalen, Nordlysstasjonen, sample 3/1, 30.vi.2009 (T. Solhøy) 22 specimens; U.S.A.: Alaska, College (?), 1 mi. N (?) 4 vi.1948 (S. Lienk) female; (note, this specimen was identified by M. Hammer and formed part of her study on Alaskan Oribatida ( Hammer 1955)) ; the specimen was remounted by R.A. Norton 25.xi.1983 ( RNC); Canada: Northwest Territories, Bernard Harbour, 10.vii.1988 (J. Troubridge) from litter under willows; from Silene acaulis (L.) on acid slope; from Astragalus alpinus L.; 11.vii.1988, from mouse nest; Banks Island, Nanuk, 73°05’N 123°23’W, 20.viii.1974 (T. Beck, V. Day) from sparse tundra vegetation; Yukon Territory: nr. Spring River, 69°10’N 138°30’W, 18.i.1971 (P. Kevan) frozen (-50F) when collected; Blow River, 68°56’N 137°06’W, 7.vii.1987 ( VBP) from litter of tall grass on river bank; from willow litter and moss in small gorge; from very rich Alnus, Ribes, Salix litter on bluffs above river; from Alnus, Spiraea, Ribes , Vaccinium, Artemesia litter; Running River, 68°57.5’N 137°17’W, 7.vii.1987 ( VBP) from litter of Pyrola, Saxifraga spp. , Castilleja , Epilobium , moss and lichens; Nunavut: Somerset Island, 7.viii.1974 (K. Hay) from arctic willow and moss.

Diagnosis. Total length of adult 420–490 µm, notogastral width 300–320 µm (data from Thor 1930). Integument of prodorsum, notogaster, venter and mentum micropunctate ( Fig. 1D, F ). Integument of coxisternum with very faint striae; integument of lamellae with long striae ( Fig. 1A ); integument of pedotectum I with faint reticulate pattern. Rostrum tridentate: with deep, wide, parallel-sided indentation, forming 2 lateral teeth, margin between teeth with single, medial tooth, subequal in length to lateral teeth ( Fig. 1B ). Lamella with cusp about 89 µm long, cusp about 55 µm long and 38 µm wide at level of insertion of seta le. Lamellar cusps contiguous, or not, anteromedially; separated posteromedially, leaving prodorsum visible through oval opening about 6 µm at greatest width. Translamella without tooth, about 7 µm at greatest width and depth. Medial dens on lamellar cusp about 12–36 µm long, one-third to subequal lateral dens (31–48 µm) ( Fig. 1A, 1C ). Medial dens with 0–1 teeth, lateral dens with 2– 4 teeth. Number of teeth on lateral margin of cusp varying among specimens and on either side of same specimen. Seta ro about 64 µm long, strongly barbed along length, acuminate, strongly directed medially. Setae le about 53 µm long, thick, heavily barbed, tapered. Setae in about 91 µm long, thick (less so than le), heavily barbed, tapered; mutual distance of pair about 38 µm. Bothridial setae about 84 µm long, with barbed, fusiform to clavate head, rounded distally ( Fig. 1A, 1C ), stalk short, smooth; head directed slightly anteromedially. Exobothridial setae about 19 µm long, thin, tapered. Genal tooth broad, subrectangular, with dens ventrodistally ( Fig. 1B arrow), without dens anterodorsally; with longitudinal ridge ventrally. Tutorium about 96 µm long, of which cusp about 43µm long, rectangular, distal margin with 6 dens. Custodium about 24 µm long, apex directed anteroventrally ( Fig. 1E ). Porose area Al about 10 µm in diameter. Notogaster length subequal to width. Anterior margin undulating, with small projection lateral to bothridium, with 3–5 transverse ridges. Pteromorph rounded anteroventrally. Porose areas small, Aa about 8 µm wide. Ten pairs of smooth notogastral setae present; c setae 27–30 µm, l and h series setae about 19 µm, p series setae about 16 µm. Notogastral setae positioned laterally, lm posterior to Aa; lp anterior of A1. Distance setae h 1 –h 1 about 26 µm, wider than distance p 1 –p 1 about 19 µm. Lenticulus very faint. Epimeral setae 3c and 4c subequal in length and shape to other epimeral setae. Genital, aggenital, anal and adanal setae smooth, about 10–14 µm long; genital setae 2+4, g 1 an d g 2 on anterior margin of plate. Postanal porose area oval 16 x 10 µm. Mentum without thickened ridge anteromedially, without tectum ( Fig. 1F ). Axillary saccule about 4 x 2 µm. Leg setation (I to IV): trochanters, 1-1-2-1; femora, 5-5-3-2; genua, 3(1)-3(1)-1(1)-2; tibiae 4(2)-4(1)-3(1)- 3(1); tarsi, 20(2)-15(2)-15-12. Seta l“ of genu I about 29 µm. Tarsi heterotridactylous.

Remarks. The type specimens of O. arctica , collected from Svalbard, Norway ( Thor 1930) are destroyed ( Marshall et al. 1987), but I have examined specimens collected from this island by Torstein Solhøy. Thor (1930) described the dens of the lamellar cusps as being of almost equal length. In the specimens that I have examined from Svalbard and elsewhere the relative length of medial and lateral dens is highly variable. In specimens from the same sample the medial dens can vary from one- third to subequal to the length of the lateral dens. For example, on one specimen from Yukon, medial dens 22 µm, lateral dens 31 µm on one cusp, medial dens 13 µm and lateral dens 36 µm on second cusp; on second specimen from same sample: medial dens 23 µm, lateral dens 48 µm on one cusp and medial dens 17 µm, lateral dens 44 µm on second cusp; on a third specimen medial and lateral dens were equal in length on both cusps.

Distribution and Ecology. Oribatella arctica is known from arctic latitudes of the Nearctic and Palaearctic ( Marshall et al. 1987). A subspecies, O. arctica littoralis Strenzke 1950 , has been found associated with littoral habitats in the Netherlands ( Polderman 1974), and has been used to evaluate archaeological findings ( Schelvis 1990).

Figures

FIGURE 1 A–F Oribatella arctica Thor, differential interference contrast microscope images of adult females: A, prodorsum; B, detail of rostrum, with arrow to anteroventral dens on genal tooth; C, detail of lamellar cusps; D, micropunctate pattern on notogaster; E, pteromorph and custodium, with arrow to custodium; F, mentum of subcapitulum. Scale bars: A, C = 50µm; B, D–F = 25µm.