Arctoseius Thor, 1930

Makarova, Olga L. & Huhta, Veikko, 2017, A new species of Arctoseius Thor, 1930 (Acari: Ascidae) from taiga regions of the Palaearctic, with a key to Arctoseius species of Fennoscandia, NW Europe, Zootaxa 4268 (4), pp. 554-562 : 559-560

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