Arctoseius Thor

De Moraes, Gilberto J., Britto, Erika P. J., Mineiro, Jefferson L. De C. & Halliday, Bruce, 2016, Catalogue of the mite families Ascidae Voigts & Oudemans, Blattisociidae Garman and Melicharidae Hirschmann (Acari: Mesostigmata), Zootaxa 4112 (1), pp. 1-299 : 18-19

Arctoseius Thor

FEMALE

Gnathosoma. Anterior margin of epistome with three (occasionally two or four) pointed and smooth (occasionally distally denticulate) projections. Usually h1 or h3 longest, pc intermediate and h2 shortest; insertion of h2 about in transverse line or slightly posterior to insertion of h3 (anterior in A. sexsetus Lindquist & Makarova ). Inner palp trochanter seta slightly to distinctly longer than outer seta but not elongate. Deutosternum wide, with delimiting lateral lines (usually divergent toward base, in some species subparallel or convergent posteriorly to second-third row of denticles from base; lines not distinguishable between first and third row from base in A. dendrophilus Karg ) and seven (rarely eight) rows of 8–25 denticles each. Corniculi 2–3 times as long as their basal widths (about as long as basal width in A. idiodactylus Lindquist ; about four times as long in A. brevichelis Karg and A. sexsetus ), with pointed tips, subparallel. Palp tarsal apotele two-tined. Cheliceral digits of similar lengths, ranging from short to long; fixed digit usually with 3–5 teeth (in a few species, 6–7; nine or more in A. cetratus Sellnick ), A. haarlovi Lindquist & Makarova , A. kolymensis Makarova & Petrova , A. multidentatus Evans and A. weberi Evans ) in addition to apical tooth; movable digit with two teeth (one in A. brevichelis ) in addition to apical tooth, without ventral projection.

Idiosoma. Oval or ovoid. Dorsum: podonotal and opisthonotal shields fused (not fused in A. longispinosus (Hirschmann)) , smooth or ornamented, with distinct lateral incisions at region of fusion (without incisions in A. dendrophilus , A. minutus (Halbert) , A. pulvisculus (Berlese) and some populations of A. pannonicus Willmann ), without transverse and nearly straight lines, delineated strip along lateral margins or posterior tubercles; anterior end of dorsal shield not strongly deflexed. No supernumerary setae on dorsal shield(s) or on unsclerotised lateral cuticle. Podonotal region of shield (or podonotal shield) usually with 17 pairs of setae (in some species, 14–16 or 18; z1 present; s2 usually on unsclerotised lateral cuticle); setae j1, j2 and z1 not in transverse line along anterior margin of dorsal shield. Opisthonotal region of shield (or opisthonotal shield) with 14 pairs of setae (S2 absent; in some species, 12–13). Unsclerotised lateral cuticle with 7–11 pairs of setae (in some species 4–5), including r3, which is either similar to neighbouring setae or more perpendicular to surface of idiosoma than neighbouring setae; UR setae absent. Most dorsal and lateral setae of idiosoma similar in length, short (in A. longispinosus setae usually longer than distance to subsequent setae), acicular and smooth. Ve n t e r: a pair of presternal platelets usually weakly sclerotised fused with sternal shield (distinct, not fused in A. brevichelis , A. venustulus (Berlese) and A. weberi ; totally fused with each other in A. babenkoi Makarova , A. miranalis Makarova and A. productus Makarova ). Sternal shield with three pairs of setae of similar lengths (st1–st3; st1 inserted on unsclerotised presternal region in A. bilinear Nasr ) and three pairs of lyrifissures (iv1–iv3; the latter on posterior shield margin, which is usually slightly convex, truncate or undulate, rarely concave or distinctly convex); st2 equidistant to st1 and st3. Seta st4 inserted on unsclerotised cuticle (shown on metasternal plate in the original description of A. dendrophilus ). Genital shield usually narrow, widening posteriorly but not wide enough to include iv5 or st5; posterior region usually slightly to distinctly convex (rarely truncate). One or two pairs of usually elongate metapodal plates, the anterior usually transversely oriented and the posterior longer and longitudinally oriented (the posterior minute, probably a fragmentation of the anterior in A. bilinear ). Usually with a sclerotised line and a pair of elongate platelets between genital and anal shields (none or two pairs of platelets in some species). Opisthogaster with 7–10 pairs of setae (six pairs shown in the original description of A. brevichelis ) on unsclerotised cuticle, in addition to circumanal setae (a pair of opisthogastric setae on ventrianal shield in A. euventralis Karg , A. latoanalis Karg and A. magnanalis Evans , but the first two species may belong to different genera - see notes under each of these species further in this text); anal shield usually rounded to ovoid, rarely subquadrate to semicircular; para-anal setae inserted between levels of anterior and posterior anal margins, usually much shorter than post-anal seta (rarely as long as post-anal seta) the latter not stout. Anal opening small (1/3 to 1/5 times anal or ventrianal shield length), from slightly anterior to slightly posterior to shield centre. Anterior section of endopodal shield normally developed and fused with sternal shield, or reduced and represented by small projections from the sternal shield between coxae I–II and/or II–III (often in this case concurrently represented by platelets between coxae); section behind sternal shield usually reduced to an elongate (in some species triangular) platelet beside coxa IV (not shown in the original description of some species); sometimes endopodal shield totally reduced ( cetratus group). Exopodal shield indistinct or fragmented at several places along coxae II–IV.

Peritreme. Ranging from short, extending from stigma to posterior margin of coxa II, to long, almost reaching level of z1; about as wide as or narrower than diameter of stigma. Peritrematic shield narrow or wide; not fused with dorsal shield or fused with it by a narrow extension beyond tip of peritreme; extending posteriorly around coxa IV, apparently incorporating remnant of exopodal shield in this region ( A. multidentatus with distinct remnant laterad of coxa IV).

Legs. All legs with pretarsi. Setation of legs I–IV, genu: 12, 10, 7, 7; tibia: 12, 9, 7, 7 (or 6). Leg II not distinctly different from other legs. Legs without macrosetae. Setae al1, pl1, ad2 and pd2 of tarsi II–IV not elongate. Spermathecal apparatus. Distinct in A. babenkoi , A. magnanalis .

MALE

Gnathosoma similar to female, but fixed cheliceral digit with 2–14 teeth in addition to apical tooth, movable digit with one tooth in addition to apical tooth; spermatodactyl about as long as movable digit, directed forward, tapering, curved slightly upward distally or sinuous (spoon-shaped in A. weberi ). Dorsal shield ornamentation and relative setal lengths similar to female. Presternal area similar to female. Sternogenital shield with five pairs of setae (st1–st5; four pairs in some specimens of A. tschernovi Makarova , with st5 on unsclerotised cuticle) and three pairs (iv1–iv3) of lyrifissures; not fused with ventrianal or peritrematic shields; posterior margin truncate to convex. Ventrianal shield ranging from a broad triangle, covering most of the opisthogastric surface, to a narrow triangle, or variously eroded anteriorly or laterally, including 3–7 pairs of setae in addition to circumanal setae; some species with a variously shaped ventral and a separate roundish anal shield. Endopodal shield totally fused with sternogenital shield, or section of endopodal shield beside coxae III–IV represented by a strip free or fused with sternogenital shield only by anterior end, or shield absent. Peritreme similar to female, but peritrematic shield sometimes fused with dorsal shield anteriorly ( A. semiscissus (Berlese) , A. babenkoi ). Leg II with or without spineshaped setae on the ventral face of some segments.

NOTE: there is considerable variability within each species in this genus, especially in relation to the shape of epistome, female genital and anal shields, number of teeth on fixed cheliceral digit, extent of dorsal shield, including a variable number of setae, and the shape and extent of male ventrianal shield.