Erythraeus (Parerythraeus) thomasi, Roland & Gabryś, 2020

Roland, Elżbieta & Gabryś, Grzegorz, 2020, Erythraeus (Parerythraeus) thomasi sp. nov. (Acari: Actinotrichida: Erythraeidae) from Finland, with a redefinition of Parerythraeus Southcott, 1946 stat. nov. as a subgenus and a key to species, Zootaxa 4718 (3), pp. 324-336 : 326-333

Erythraeus (Parerythraeus) thomasi sp. nov.

( Figs. 1–14 , Tabs. 1–5 )

Diagnosis. Female. Medium to large mites (length from 1767 to 2513, width 1099–1464), body oval. Palptibia with 3–5 strong and short conalae, palpgenu with 1–3 conalae and 1–2 semiconalae. Crista metopica distinct, typically formed. Anterior process, in shape of isosceles triangle, if seen. Anterior sensillary area with 6–10 stout and rigid nonsensillary setae of various lengths. Double eyes located symmetrically on each side of crista metopica. Body with a uniform cover of setae. Dorsal opisthosomal setae very characteristic, of one type, asymmetrical, regularly elliptic; dorsal, convex side with four regular rows of denticles along the axis, 8–9(10) denticles in each row; on ventral, concave side, the keel of the setae is clearly visible, along both sides of a keel tiny setulae in several (4–6) regular rows. Ventral setae of different structure: narrow, needle-like, blunt, weakly setulose; setae closer to end of the body stouter and more setulose. Legs IV clearly longer than legs I–III, almost twice as long as the body. All legs with relatively strong, slightly asymmetrical, mucronate apically serratalae with distinct denticles.

Male. Body shape and structure as in female. Palptibia with 4 conalae, palpgenu with 1–3 conalae and 1 semiconala. Well sclerotized internal genital sclerite present.

Deutonymph. Body shape and structure as in adults but much smaller (length 1348, width 814). Palptibia with 2–4 conalae, palpgenu with 0–2 conalae. Anterior sensillary area of crista metopica with 5–9 nonsensillary setae.

Larva. Not known.

Description (based on holotype, with additional data from paratypes); metric data in Tables 1–3 .

Female. Life colour not known, brown after preservation in isopropyl alcohol. Medium to large size (length from 1767–2513, width 1099–1464). Body oval, almost twice as long as wide (LB/WB mean: 1.64).

Gnathosoma. Chelicerae narrow, dagger-shaped, retractable into idiosoma, typical for genus. Palps ( Figs. 1 , 9 ) with relatively dense setation. Setae on palptibia long, slender, covered with minute setulae. Palptarsus clavate, slightly protruding beyond palptibial odontus, with solenidia in apical part. Palptibia triangular in outline with single odontus. Odontus delicately denticulate in apical half, with small denticle at base. Ventral side of palptibia with 3–5 conalae and long, delicately setulose seta. Palpgenu with 1–3 conalae and 1–3 semiconalae.

Character Female Male Deutonymph Holotype (female)307/31

n=sample size; x=mean; - = not suitable for measuring; symbols denote the length of the structure, unless stated otherwise; SD = standard deviation. For other abbreviations see: Southcott (1961); Welbourn & Young (1987); Gabryś (1992, 1999); Gabryś & Roland (2016, 2018).

Aspidosoma. Crista metopica ( Fig. 2 ) well defined. Rod between anterior and posterior sensillary areas linear, 19 wide, on average. Anterior sensillary area slightly oval (width:length ratio 1.14), with a pair of sensillary setae (ASens), anterior to middle of area; ASens slightly setulose in apical part (at 1/3 length). Anterior sensillary area with 6–10 rigid, scaly serrate nonsensillary setae (AM) of various lengths, mostly 76–185 ( Fig. 3 ). Anterior process, 90 long on average, in shape of isosceles triangle, if seen ( Fig. 2 ). Posterior sensillary area oval (length:width ratio 1.3 on average), with two smooth sensillary setae (PSens). PSens longer than ASens. Eyes ( Fig. 2 ) symmetrical at sides of crista metopica, sessile, composed of two round lenses; anterior lens slightly smaller than posterior lens.

Opisthosoma. Uniformly covered with setae. Dorsal opisthosomal setae ( Figs. 5a, b , 10, 11 ) very characteristic, of one type, not very long, slightly longer towards end of body, from 37 at mid part (mdS) to 55 in posterior part of opisthosoma (pdS). Setae rigid, slightly arched, elliptical in outline. Dorsal side of seta with 4 rows of distinct ‘denticles’ arranged symmetrically along setal axis, 8–9 (10) denticles in one row. Ventral side with exposed keel, with 4–6 regular rows of tiny spikes at its sides. Ventral opisthosomal setae ( Figs. 4 , 12 ) of different shape, needle-like, blunt, slightly setulose; setae closer to end of body stouter and more clearly setulose.

Genital-anal region ( Figs. 7, 8 ). Genital opening ( Fig. 7 ) surrounded with centrovalves (internal genital sclerites) and epivalves (external genital sclerites). Setae on valves needle-like, smooth, 49 long on average. Anus ( Fig. 8 ) with two pairs of valves. Internal anal sclerites membraneous. External anal sclerites slightly sclerotized. Valves with 18 (on average) needle-like, smooth setae, 45 long on average. ExGL/AnL = 2.85.

Podosoma. Legs IV> legs I> legs II and III. Legs IV noticeably longer than others, almost twice as long as body. All legs with asymmetrical, mucronate apically serratalae ( Figs. 6 , 13, 14 ). Dorsal side of serratala with two rows of distinct denticles (5–6 in one row). Denticles in a shape of isosceles triangle, relatively deeply incised. Ven- tral side of serratala with clearly visible axis. n=sample size; x=mean; L = length; W = width; Pa = palp; Fe = femur; Ge = genu; Ti = tibia; Ta = tarsus; Cl = palptibial claw (= odontus).

Character Female Male Deutonymph Holotype (female)307/31

Ventral side of tarsus I with 2–3 vestigialae in distal part and one in proximal part. Tibia I, genu I, telofemur I with one vestigiala. Tarsus II, tarsus III, and tarsus IV with one vestigiala in distal and proximal parts. Legs I more densely covered with solenidia than legs II, III, and IV. Solenidia on legs II, III, and IV concentrated mainly on ventral side of tarsus II, tarsus III, and tarsus IV; single solenidia also along legs and near joints.

Male. Shape and size of body similar to female but smaller. Palptibia with 4 conalae, palpgenu with 1–3 conalae and 1 semiconala. Strongly sclerotized internal genital sclerite present.

Deutonymph. Shape of body similar to adults, much smaller (1348 long, 814 wide). Palptibia with 2–4 conalae, palpgenu with 0–2 conalae. Nonsensillary setae on anterior sensillary area of crista metopica (AM) less numerous (5–9). Genital region with a pair of smooth needle-like genital setae. ExGL/AnL = 0.40.

Type locality. Southwestern Finland

Distribution. Finland.

Etymology. The name of the species has been derived from the given name of the senior author‘s husband— Thomas.

Type material. Holotype. Female. Slide No. 307/31; Finland, biogeographic province: Varsinais-Suomi, local- ity: 670: 25 V, Kaarina Kuusiston Kartano; Kuiva keto (= dry field) 13.6.– 15.7.1989, leg. S. Koponen.

Paratypes. 24♀♀, 4♂♂, 3DN, distributed as in ‘List of localities’ presented below.

The description of the specimens studied included the following data: geographic position according to Grid 27 0 system, name of the region, island, or a town, habitat, date of collection, name of the collector.

List of localities. 1) 665:21; Nauvo, Lökholm; dry meadow with junipers; 10.8.1969 –1970; P. T. Lehtinen; 2♀♀. 2) 666:20; Nauvo , Berghamn , Boskär ; dry meadow (7); 30.5– 24.7.1990; K. Heikka, P. T. Lehtinen ; 1DN. 3) 666:20; Nauvo , Berghamn , Boskär; dry meadow (11); 30.5.– 24.7.1990; K. Heikka, P. T. Lehtinen; 1♀, 1♂ , 1DN. 4) 666:20; Nauvo , Berghamn , Boskär; dry meadow (9); 30.5.– 24.7.1990; K. Heikka, P. T. Lehtinen; 2♀♀ . 5) 670:25; Kaarina Kuusiston Kartano ; dry field; 13.6.– 15.7.1989; S. Koponen; 12♀♀, 2♂♂ , 1DN. 6) 670:25; Kaarina Kuu- siston Kartano; dry field; 15.7.– 23.9.1989; S. Koponen; 7♀♀, 1♂ . 7) 672:26; Tarvasjoki , Eurankylä; south slope; 13.7.– 3.8.1969; S. Kännö; 1♀ .

Character Female Male Deutonymph Holotype (female)307/31

n=sample size; x=mean; I = first pair of legs; II = second pair of legs; III = third pair of legs; IV = fourth pair of legs; Cx = coxa; Tr = trochanter; bFe = basifemur; tFe = telofemur; Ge = genu; Ti = tibia; Ta = tarsus; H = height; L(∑) =sum of lengths Cx+Tr+bFe+tFe+Ge+Ti+Ta.

Holotype and paratypes are deposited in the Acarological Collection of the Department of Zoology , Faculty of Biological Sciences, University of Zielona Góra, Poland .

Remarks. The details of the structure of the dorsal opisthosomal setae are the most important character that differs Erythraeus (Parerythraeus) thomasi sp. nov. from other species of the subgenus. The full data on this feature and other differentiating characters are given in Tables 4 and 5. Moreover, Erythraeus (Parerythraeus) thomasi sp. nov. differs from other species of the subgenus in having a set of characters given below.

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) serratociliatus in having conalae on palpgenu (vs. lack of conalae), more AM setae (6–10 vs. 3), and leg IV: LB ratio 2.04 (vs. 2.54).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) elegans in having conalae on palpgenu (vs. lack of conalae), more AM setae (6–10 vs. 5), leg IV: LB ratio 2.04 (vs. 2.22), and weaker serratalae of ‘ regalis’ type (vs. very strong serratalae of ‘ gregoryi-tragardhi ’ type).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) orientalis in having stronger serratale of ‘ regalis ’ type with denticles (vs. narrow, weakly developed serratalae of ‘ rupestris-adpendiculatus ’ type without denticles), more AM setae (6–10 vs. 5), and leg IV: LB ratio 2.04 (vs. 1.99).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) plumosus in having stronger serratale of ‘ regalis ’ type with denticles (vs. narrow, weakly developed serratalae of ‘ rupestris-adpendiculatus ’ type without denticles) and leg IV: LB ratio 2.04 (vs. 2.81).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) italicus in having fewer AM setae (6–10 vs. 18–20), fewer conalae palpgenu (1–3 vs. 6), leg IV: LB ratio 2.04 (vs. 1.73) and stronger serratale of ‘ regalis ’ type (vs. delicate, rather slim serratalae of ‘ phalangoides ’ type).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) delhiensis in fewer AM setae (6–10 vs. 12), fewer palpgenu conalae (1–3 vs. 6–7), fewer palptibia conalae (3–5 vs. 7) and leg IV: LB ratio 2.04 (vs. 2.33).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) gregoryi in having fewer palptibia conalae (3–5 vs. 7), leg IV: LB ratio 2.04 (vs. c. 3.26), and weaker serratalae that are mucronate apically of ‘ regalis’ type (vs. very strong serratalae not mucronate apically of ‘ gregoryi-tragardhi ’ type).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) mirjavehi in having fewer palptibia conalae (3–5 vs. 6), more AM setae (6–10 vs. 5), and leg IV: LB ratio 2.04 (vs. 3.32).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) nigritiensis in having fewer palpgenu conalae (1–3 vs. 4), fewer palptibia conalae (3–5 vs. 6), and leg IV: LB ratio 2.04 (vs. 3.97).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) indicus in having more AM setae (6–10 vs. 5), and leg IV: LB ratio 2.04 (vs. 3.27).

Erythraeus (Parerythraeus) thomasi sp. nov. differs from E. (P.) tragardhi in having weaker serratalae that are mucronate apically, and of the ‘ regalis’ type; on the dorsal side, laterally, with two rows of clearly developed denticles, 5–6 in each row; denticles slightly curved, in the outline of an isosceles triangle, quite deeply indented (vs. very strong serratalae, not mucronate apically, of ‘ gregoryi-tragardhi ’ type; on the dorsal side, laterally, with two rows of clearly developed denticles, 8–10 in each row; denticles at the base considerably broader and resemble an equilateral triangle in outline; the incisions in the denticles are shallow) and leg IV: LB ratio 2.04 (vs. 1.7).

Figures

FIGURES 1–8. Erythraeus (Parerythraeus) thomasi sp. nov. (1) left palpgenu, palptibia and palptarsus, medial aspect; setae on palptarsus omitted; (2) crista metopica with double eyes; (3) nonsensillary seta (AM); (4) midventral opisthosomal seta (mvS); (5) middorsal opisthosomal seta (mdS); a. dorsal view; b. lateral view; (6) serratala on genu IV; a. dorsal view; b. lateral view; (7) external genitalia; (8) anus.

FIGURES 9–14. Erythraeus (Parerythraeus) thomasi sp. nov. (9) left palp, medial aspect; (10) middorsal opisthosomal setae (mdS) dorsal view; (11) middorsal opisthosomal setae (mdS) lateral view; (12) midventral opisthosomal setae (mvS); (13) serratalae on genu IV, dorsal view; (14) serratalae on genu IV, lateral view.