Arctoseius Thor 1930

Key to species of Arctoseius Thor, 1930 of Fennoscandia, North-Western Europe

The key is mainly based on females, but reliable identification often requires investigation of males. Total length refers to length of dorsal shield.

1. Gnathotectum biramous; incisions of dorsal shield very deep, their length about 1/3 of dorsal shield width; tibia IV with six setae; peritremes not extending anteriorly beyond mid-level of coxae II; in female sternal shield weakly sclerotized, lacking endopodal elements, nearly rectangular................................................................... 2

- Gnathotectum triramous; incisions of dorsal shield shorter or absent; tibia IV with seven setae (exception A. sexsetus); peritremes of different length; sternal shield with or without angular extensions formed by endopodal elements between coxae I–II and II–III........................................................................................... 4

2. Dorsal shield setae longer, most of them extending to base of next posterior seta in series, seta Z2 reaching or surpassing insertion of Z 3; opisthogastric soft integument with eight pairs of ventral setae (ZL 3 absent); fixed digit of chelicera with 3–4 teeth; in male, dimorphically modified seta on telotarsus II absent. Female 350–420 µm, male 270–310 µm. Cosmopolitan..................................................................................... semiscissus (Berlese, 1892)

- Dorsal shield setae shorter, most of them not extending to base of next posterior seta, seta Z2 not reaching insertions of Z 3; opisthogastric soft integument with nine pairs of ventral setae (JL 1– JL 5, ZL 1– ZL 4); fixed digit of chelicera with six or more teeth; in male, one ventral seta on telotarsus II swollen basally, with sharply curved hair-like tip...................... 3

3. Epigynal shield usually with posterolateral margins abruptly expanded beyond the genital setae; fixed digit of female chelicera with six teeth (in male, 10–12 teeth); in general larger species. Female 350–420 µm, male 300–310 µm. European Arctic, Siberia, Chukotka............................................................ nikolskyi Makarova & Petrova, 1992

- Epigynal shield usually with almost parallel or gradually divergent posterolateral margins beyond the genital setae; fixed digit of adult chelicera with 7–11 teeth; in general smaller species. Female 270–360 µm, male 250–280 µm. Cosmopolitan........................................................................................ cetratus (Sellnick, 1940)

4. Mid-lateral incisions of dorsal shield poorly visible or absent; dorsal shield less than 350 µm in length.................. 5

- Mid-lateral incisions of dorsal shield present, clearly visible; dorsal shield more than 350 µm in length................. 7

5. Mid-lateral incisions of dorsal shield present but often poorly visible, reticulate ornamentation developed on both podonotal and opisthonotal regions of shield; sternal shield with anterolateral and posterolateral angular extensions formed by endopodal elements. Female 285–340 µm, male 260–270 µm. Europe, South Siberia.................... insularis (Willmann, 1952)

- Mid-lateral incisions of dorsal shield absent, shield ornamentation distinct pronounced mainly in podonotal region, opisthonotal region smooth or punctate; sternal shield with or without lateral angular extensions.............................. 6

6. Podonotal region of dorsal shield deeply foveate, opisthonotal region smooth, most of dorsal shield setae clearly daggershaped, posteromedial setae J 1–3 almost reaching bases of next posterior setae in series; sternal shield without lateral angular

extensions; in male, spermatodactyl much thinner than cheliceral digits. Female 325–340 µm, male 235 µm. Europe........................................................................................ dendrophilus Karg, 1969 - Anterior part of dorsal shield with squamous ornamentation, opisthonotal region punctate; dorsal shield setae needle-like or with slightly dilated base, posteromedial setae J 1–3 clearly not reaching bases of next posterior setae; sternal shield with well developed lateral angular extensions; in male, spermatodactyl as thick as cheliceral digits. Female 270–325 µm, male 250–260 µm. Holarctic...................................................................... minutus (Halbert, 1915)

7. Female with large, almost quadrate ventri-anal shield bearing besides three circum-anal setae, one pair of opisthogastral setae (JL 3); dorsal shield poorly reticulate with elongate caudal setae (J 1–4 11–16 µm, Z 4 42 µm, Z 5 58 µm); in male, spermatodactyl straight, apically pointed. Female 440–480 µm, male 380–400 µm. Europe, Caucasus........ magnanalis Evans, 1958

- Female with anal shield of different size bearing only three circum-anal setae; dorsal shield ornamentation varying; in male, spermatodactyl of different form.........................................................................8

8. Female with anal shield very large, twice as wide as the narrow sternal shield, the latter without lateral angles; dorsal shield with rather long setae (j 5, J 4 24 µm, Z 4 45–50 µm, Z 5 67–69 µm); tarsus I plump; claws I of the same size as on legs II–IV; cheliceral digits much shorter than corniculus (lch/lco 0.74–0.77). Female 390–422 µm. Europe, Caucasus................................................................................................. eremitus (Berlese, 1918)

- Female anal shield narrower than sternal shield; sternal shield with or without lateral angles; dorsal shield setae of different length; tarsus I plump or of normal proportions, with claws of different size, cheliceral digits shorter or longer than corniculus................................................................................................... 9

9. Cheliceral digits very short, much shorter than the robust corniculus (lch/lco 0.64–0.76), digitus mobilis with one tooth; sternal shield lacking endopodal elements, with parallel lateral margins; dorsal shield smooth, opisthonotal region with 13 pairs of setae (J 1 absent) and remarkably elongate setae Z5 (52–68 µm, while j 5 20–29 µm, J 2–4 18–22 µm); peritremes anteriorly not extending beyond anterior margin of coxa II. Female 375–440 µm, male 340 µm. Palaearctic........ brevichelis Karg, 1969

- Cheliceral digits longer, often longer than corniculus (lch/lco not less than 0.74), digitus mobilis with two teeth; sternal shield including endopodal elements, with lateral angles; dorsal shield smooth or reticulate, with or without setal deficiency, seta Z5 remarkably elongate or not; peritremes of different length.....................................................10

10. Peritremes commonly extremely short, extending anteriorly only to mid-level of coxa III; corniculus of normal proportions (lco/lD 6.9–9.1 %); dorsal shield smooth, its opisthonotal region normally with 13 pairs of setae (only one pair of setae present in area usually occupied by J 4 and Z 4). Female 368–468 µm, male 332–376 µm. Circumpolar............................................................................................... haarlovi Lindquist & Makarova, 2011

- Peritremes longer, extending anteriorly at least to mid-level of coxa II; corniculus of normal proportions or elongate (lco/lD 11.5–13.1%); dorsal shield smooth or reticulate, its opisthonotal region with 13–14 pairs of setae (if deficient, setae S 1 absent).................................................................................................. 11

11. Peritremes not extending anteriorly beyond mid-level of coxa II; dorsal shield smooth; para-anal setae relatively long, at least 0.7 as long as post-anal seta........................................................................... 12

- Peritremes extending anteriorly at least to level of coxa I; dorsal shield smooth or reticulate; para-anal setae relatively short, about half as long as post-anal seta...................................................................... 13

12. Dorsal shield without podonotal seta z 3 and opisthonotal seta S 1; corniculi large (lCo/lD 11.5–13.1 %), longer than cheliceral digits (lCh/lCo 0.74–0.93); fixed digit of chelicera terminating with trident, behind which one denticle present; tibia IV with six setae; tarsi II–IV with needle-shaped subapical ventral setae; in male, ventrianal shield broadly oval, metapodal platelets free; dimorphically modified setae on leg II absent; spermatodactyl straight, hardly protruding beyond tip of digit. Female 444–552 µm, male 404–464 µm. East Europe, Siberia, Far East, Alaska............ sexsetus Lindquist & Makarova, 2011

- Dorsal shield with podonotal seta z 3 and opisthonotal seta S 1; corniculi relatively small (lCo/lD 7.7–9.6 %), slightly shorter than cheliceral digits (lCh/lCo 1.03–1.17); fixed digit of chelicera polydont; tibia IV with seven setae; tarsi II–IV with subapical ventral setae av -1 and pv -1 stout and blunt; in male, ventrianal shield relatively wide, subtriangular, incorporating metapodal platelets; dimorphically modified setae on leg II well developed; spermatodactyl tightly sinuate, half protruding beyond tip of digit. Female 528–616 µm, male 446–552 µm. East Europe, Siberia, Chukotka... koltschaki Makarova & Lindquist, 2013

13. Dorsal shield clearly uniformly reticulate; anal shield and sternal shield almost of the same size. Female 468–512 µm. Finland, Altai Mts............................................................................... ambiguus sp. nov.

- Dorsal shield almost smooth or partly (anteriorly and laterally) reticulate; anal shield clearly smaller than sternal shied; female 356–407 µm........................................................................................ 14

14. Presternal platelets membranous, fused with sternal shield; sternal shield almost smooth, some ornamentation lines visible laterally; dorsal setae short and uniform (j 5 15–20 µm, J 1–4 11–16 µm, J 1–3 more than half as long as distance to next seta in series), Z5 (18–23 µm) slightly longer than other dorsal setae. Female 356–402 µm, male 332 µm. Europe, South Siberia........................................................................................ pristinus Karg, 1962

- Presternal platelets well sclerotized, semicircular, free; sternal shield intensively uniformly reticulate; dorsal setae of middle length (j 5 19–28 µm, J 1–4 18–28 µm, J 1–3 a little shorter than distance to next seta in series, Z5 (30–42 µm) clearly longer than other dorsal setae. Female 360–407 µm. Europe.......................................... resinae Karg, 1969