Arctoseius ambiguus Makarova & Huhta

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 : 555-559

Arctoseius ambiguus Makarova & Huhta sp. nov.

( Figs 1–11 )

Material examined. Holotype, female: Finland, Kolari (67°29’ N, 24°7’ E), wet coniferous forest ( Picea abies , Pinus sylvestris , Vaccinium spp., mosses), soil/litter sample, 4 August 2005, leg. V. Huhta, deposited in the Zoological Museum of Helsinki University , Finland (MusZHki). Paratypes: two females , same data as the holotype (MusZHki), two females , same data, Zoological Institute of the Russian Academy of Sciences, Saint Petersburg, Russia ; four females, South Siberia , NE Altai, Turochak district , Altyn-Tu Range, Archa Mt. (51°31' N, 87°26' E), 1600 m a.s.l., light forest ( Pinus sibirica , Betula rotundifolia ) with screes, from soil sample, 27 June 2006, leg. N.V. Ananieva [Vladimirova] (Siberian Zoological Museum, Institute of Systematics and Ecology of Animals of the Russian Academy of Sciences, Novosibirsk, Russia) . Other material: one female: Finland, Jyväskylä (62°13’ N, 25°29’ E), old mesic coniferous forest ( Picea abies , Pinus sylvestris , Vaccinium myrtillus , mosses) August 1994 (this specimen was lost during postal transfer).

Diagnosis (female only). Dorsal shield with lateral incisions, reticulate, with full set of relatively short setae. Sternal shield fused with endopodal elements I–II and II–III, reticulate. Anal shield rather large, longer than sternal shield, broadly oval or roundish-triangular, widest posterior to level of gv3, its lateral margins uneven, with roundish ledges; post-anal seta twice or more longer than para-anal setae. Peritremes long. Gnathotectum with three simple prongs. Corniculus and chela of normal proportions, fixed digit with four teeth. Claw I smaller than claws II–IV. Tibia IV with seven setae.

Description (female). Middle sized, short-legged, yellowish or brownish mites. Idiosomal shields moderately sclerotized, mainly reticulate. Most dorsal idiosomal setae and leg setae short, needle-shaped. Some setae of tarsi I and IV elongated and hair-like distally.

Idiosomal dorsum ( Figs 4, 5 ). Dorsal shield 468–512 x 264–288, lD/wD ca 1.72–1.82; its maximal width at level of opisthonotal setae S 3 ( Fig. 5 ); lateral incisions of moderate length (30–44), transverse, relatively narrow, often extended by lyrifissure idz 6; shield reticulation more distinct laterally. Podonotal region with 17 pairs of simple setae (z 3 present); s 2 usually on soft cuticle, seldom asymmetrically on shield margin. Opisthonotal region with 14 pairs of setae (S 2 always absent). Among podonotal setae, z 1 (12–18), s 1 (18–22) and s 2 (18–23) shorter than most others (18–33). On opisthonotal region, setae J 1–4 (13–21) shorter than others (19–30), except J 5 clearly shortest (12–17) and Z5 clearly longest (35–42); J (1–4) min/jmax 0.62–0.76, Z5/ (Z 5- Z 5) 0.35–0.46; (J 4- J 4) / (J 3- J 3)1.33–1.72. Dorsal shield with five pairs of gland pores: poorly visible gdj 2, gdj 4, gdz 6, and distinct gdZ 3, gdZ 4. All marginal setae on soft cuticle; four setae in series r (r 2–5; their length 19–27) and 4–5 setae in series R (R 1–4 or R 1-5; 15–22); setae of series R usually inserted ventrally ( Fig. 8 ).

Idiosomal venter ( Figs 1 , 6, 8, 9 ). Base of tritosternum trapezoidal (21–23 x 16 –18); laciniae (68–80) with sparse large barbs, free for ca 0.8–0.9 of lengths, their fused basal area fringed anteriorly ( Fig. 1 ). Presternal platelets small, weakly sclerotized, lineate, adjacent to sternal shield ( Fig. 8 ). Sternal shield as long (108–115) as wide (102–116), lSt/wSt 0.97–1.06, fused with endopodal platelets between coxae I–II and II–III. Narrow distal part of endopodal projection between coxae I–II nearly bacilliform, sometimes separated, their lateral part encompassing opening of gland gvb. Sternal shield entirely reticulated with ornamentation more distinct in lateral parts; anterior margin straight or slightly concave; posterior margin more or less straight. Sternal shield with typical setae st 1–3 (26–35) and lyrifissures iv 1–3. Setae st 4 (24–28) on soft cuticle. Endopodal strips between coxae III and IV free, rather narrow. Epigynal shield narrowly flask-shaped (118–136 х 47–52), reticulated posteriorly, fully punctate with dots much denser in anterior part ( Fig. 8 ); its hyaline flap well distant from sternal shield, and posterior margin broadly convex; setae st 5 (24–26) and paragenital poroids iv 5 on soft cuticle. Opening of gland gv 2 on soft cuticle between st 5 and end of peritrematal-exopodal strip. Postgenital platelets not visible. Anal shield relatively large (116–124 x 101–120; [lAn x wAn] / [lD x wD] 8.4–10.6 %), slightly longer than wide (lAn/wAn 1.03–1.19), broadly oval or roundish-triangular, widest posterior to level of gland gv 3; its lateral margins bent, with roundish ledges of different size ( Figs 8, 9 ); shield weakly reticulate anteriorly and coarsely punctate laterally and especially posteriorly; post-anal seta (44–49) twice or more longer than para-anal setae (20–22); papillae of cribrum forming rows and arcs. Opisthogastral setae (8–10 pairs, JV 1–5, ZV 1–5; ZV 3 and ZV 5 often omitted) of varying length, JV 5 usually longest (32–36), ZV 1 usually shortest (14–16); among others, setae in series JV (20– 34) usually longer than setae in series ZV (16–26). Anterior metapodal platelets small, of variable form; posterior metapodal platelets elongate oval (32– 40 x 7–10). Exopodal platelets between coxae II and III, as well as between coxae III and IV, small rudimentary ( Fig. 6 ), not visible in ventral aspect. Peritrematal shield normally developed ( Figs 4 , 8 ); its posterior edge fused with exopodal strip surrounding coxa IV posteriorly ( Fig. 8 ); poroids ip 1, ip 2 and gland pores gp 1, gp 2 present. Peritreme not shortened (226–240 х 9–11), extending to frontal level of seta j 2 anteriorly ( Fig. 4 ). Spermathecal apparatus not visible.

Gnathosoma ( Figs 3 , 7, 10, 11 ). Gnathotectum (16–22 x 30 –40) triramous, with simple prongs of almost equal size ( Fig. 3 ). Subcapitulum almost as long (108–112) as wide (100–104) ( Fig. 7 ). Deutosternum with seven rows of denticles (12–20 denticles in each row); groove delineated laterally, slightly wider in the middle (up to 19). Hypostomatic setae hp 1 (33–36) and hp 3 (36–38) longer than hp 2 (19–21) and pc (22–26); all setae needle-like, attenuate. Corniculi small, of normal proportions, 29–34 х 10–12; lCo/lD 6.10–6.64 %. Internal malae slightly shorter than corniculi, with lateral margins fimbriated basally. Chelicera medium-sized ( Figs 10, 11 ), its length without basal segment 108–116; cheliceral digits of moderate size (47–50, lCh/lD 9.22–10.09 %), half as long again as corniculus (lCh/lCo 1.44–1.64). Fixed digit with a row of three teeth in paraxial position, and pilus dentilis and one tooth in antaxial position. Movable digit bidentate. Palp length 148–162; internal seta of trochanter (30– 35) one third longer than external seta (22–26); palpi with typically specialised setae on femur (al 20–21) and genu (al 1 15–16, al 2 20–21) strong, cultriform.

Legs ( Fig. 2 ). Legs relatively short (I 408–464, II 312–364, III 278–330, IV 364–404); leg I clearly shorter than dorsal shield, lExI/lD 0.85–0.92. Length of tarsi I 108–128, II 88 –102, III 80 –92, IV 112–127; tarsi shortened: lT IV /lD 0.23–0.25, lT III /wT III 2.94–3.29; tarsus I dilated distally. Legs II, IV slightly thicker than legs I, III. Leg chaetome as described for the genus ( Lindquist & Evans, 1965); tibia IV with seven setae, pl present. Most leg setae simple, short or of moderate lengths; length of pd 2 on genu II (16–21) clearly shorter than width of segment (44–48). Tarsi II–IV each with some rather long setae (up to 64 on tarsus IV), many of them with piliform tips; with subapical setae al 1, pl 1 (14–17) and av 1, pv 1 (13–16) about equally distant from tarsus apex ( Fig. 2 ), av 1and pv 1 noticeably thicker. Ambulacrum I on pedicellate base, claws I (12) smaller than claws II–IV (15–18). Tarsus I distally with seven rod-like solenidia (five apical, two subapical); length of sensillum with lanceolate apex 30–32. Ambulacra of legs II–IV (length 32–38) with rather long paradactyli (22–24) extending clearly beyond apices of claws. Tarsi II–IV with apical setae ad 1 and pd 1 threadlike, approximately as long (26–30) as ambulacrum.

Male. Not found.

Remarks. Females of A. ambiguus are similar to those of A. venustulus ( Berlese, 1916) . They both possess fully reticulated sternal and dorsal shields (in the former species, reticulation is more pronounced laterally) and relatively large, posteriorly dilated anal shield. However, the idiosoma in A. ambiguus is larger (dorsal shield length 468–512 instead of 365–445) and wider (lD/wD 1.72–1.82 instead of 1.95–2.12). Dorsal setae in the female of the new species are in general longer and more heterogeneous, setae j 2-6 [20–28] usually longer than J 1-4 [12– 21] (weakly distinguished in A. venustulus , j 5= J 1=10 µm), seta Z 5 are significantly longer than other opisthonotal setae, particularly in the series J (length ratio Z 5/ J 1 1.9–2.4 instead of 1.3 in A. venustulus ). In A. ambiguus , the lateral margins of the anal shield often have broad ledges as in Fig. 9 (usually almost smooth in A. venustulus ); posterior and lateral parts of the shield are coarsely punctate (alternatively reticulate to different degree and finepunctate). The gnathotectum of A. ambiguus is wider (width/length ratio 1.8–2.6 instead 1.1–1.7). The sternal shield in A. ambiguus is clearly reticulate only in the lateral parts (totally and evenly so in A. venustulus ), and the presternal platelets are weakly sclerotized, abutting the sternal shield (well sclerotized, separated in A. venustulus ).

Variability. The morphological variation in A. ambiquus is minimal and concerns mainly the number of opisthogastral and posterior marginal setae of the R series ( Fig. 8 ), the position of seta s 2 (rarely on the dorsal shield margin) and the development of lateral protuberances on the anal shield ( Figs 8, 9 ).

Etymology. The specific name ambiguus highlights the absence of pronounced, easily recognisable differential features in this new species.

Distribution and ecology. At present the new species is known only from Finland and Altai Mts., South Siberia. Such distant records possibly reflect either an insufficient level of our knowledge, or peculiarities of Arctoseius bionomy. All specimens were collected from soil and litter in forests of different humidity. Forest soil is principally a stable environment, but may include unstable and scattered microhabitats. Thus the inclination of the genus to eutrophic and temporary substrata as well as their phoretic associations with dipterans (see Makarova 1999) may be involved.

Figures

FIGURES 1 – 5. Arctoseius ambiguus sp. nov., female. 1. tritosternum; 2. ambulacrum and tarsus II distally, ventral aspect; 3. gnathotectum; 4. peritrematal region; 5. idiosomal dorsum. Scales: 1 – 2 25 µm, 3 – 5 50 µm.

FIGURES 6 – 11. Arctoseius ambiguus sp. nov., female. 6. acetabula II – IV and exopodal platelets; 7. subcapitulum; 8. idiosomal ventrum; 9. anal shield; 10. cheliceral digits, dorsal aspect; 11. chelicera without basal joint, paraxial aspect. Scales: 6 – 9 50 µm, 10 – 11 25 µm.