Arrenurus (Truncaturus) chukotkaensis, Tuzovskij, 2020

Tuzovskij, Petr V., 2020, Description of a new water mite of the genus Arrenurus (Acari, Hydrachnidia: Arrenuridae) from Chukotka, Zootaxa 4802 (2), pp. 383-390 : 383-388

Arrenurus (Truncaturus) chukotkaensis sp. n.

( Figs 1–22 )

Type series. Holotype: male, slide 2571, Asia, Russia, Chukotka, Tenka District,small sedge-sphagnum bog near village Agrobasa , 8. 08. 1979 . Paratypes: From the same locality as holotype, 1 female 26. 06. 1979, 1female 7.07. 1979, 1fe- male, 2 males 8. 08. 1979 and 8 larvae reared in laboratory . Additional material: Chukotka, Anadyr District, small tundra pools near settlement Markovo , 1 male 8.08.1981, 1 male 12.08. 1981 and 1 male 3.09.1981.To obtain larvae, water mites were maintained in laboratory (with room temperature, natural day-night conditions). Eggs and larvae obtained from single female in glass with diameter 10mm, and a height 15 mm .

Description. Larva. Colour red. Dorsal plate ( Fig. 1 ) in unengorged larva covers nearly whole dorsum, bearing five pairs of setae (Fch, Fp, Vi, Oi and Hi), narrow and truncate anteriorly, indented near anterior eyes, and widened near Hi. Setae Hi longest, Fch, Fp and Oi subequal in length and a little shorter than Vi.Thichobothria Fp are trifurcate,and Oi simple and not furcate. Seven pairs of setae (Oe, He, Sci, Sce, Li, Le, Si) situated in soft integument, Oe longest, Si shortest, other setae (He, Sci, Sce, Li and Le) subequal. Medial margin of coxal plates I and III longer than medial margin of coxal plates II ( Fig. 2 ). Coxal plates I and II each with posteromedial apodemes directed laterally ( Fig. 2 ). Setae C2 longer than C1, C4 shorter and heavier than C3 and not reaching posterior margin of coxal plate III; Pi longer than Pe. All coxal plates and dorsal plate with reticulation. Setae Ci much longer than Se,Pe longer than Pi. Excretory pore plate ( Figs 3–5 ) nearly triangular, pointed anteriorly (sometimes with small anterior median projection), widest posteriorly with strong convex posterior margin; as long as wide or a little longer than wide (L/W ratio 1.00–1.17). Excretory pore plate setae (Ai and Ae) reduced and represent by alveoli, Ai located moderately away from anterior corner, Ae posterior to the center of plate flanking excretory pore; distance between setae Ae-Ae almost twice longer than distance between Ai-Ai. Basal segments of chelicerae relatively large, with slightly convex lateral margins ( Fig. 6 ). Chela small crescent-shaped, with two minute subapical teeth ( Fig. 7 ). Pedipalps short ( Fig. 8 ): P-1 very short, without setae; P-2 with single dorsal setae a little posterior to middle of segment; P-3 with very long, thick proximal seta and comparatively short, fine dorsodistal one; P-4 with two thin proximal setae, one thick, spine-like seta and massive dorsodistal claw; P-5 small with one rather long solenidion, and seven simple setae: one very long, thick seta, three moderately long, thick setae, one curved pectinate seta and two short setae (thick and thin). Legs moderately slender. Shape and arrangement of setae on legs segments as shown in Figs 10–12 . Total number of leg setae, excluding eupathidia, as follows (specialized setae indicated in parenthe- sis): I-Leg-1–5: 1, 7, 5 (s), 9 (2s), 14 (s, ac); II-Leg-1–5: 1, 7, 5 (s), 11 (2s), 14 (s, ac); III-Leg-1–5):1, 6, 5 (s), 10 (s), 11. I-III-Leg-2 setae Fe6 (after Prasad & Cook 1972) represented in the form of setal bases only and usually hardly visible. Number of thickened distal setae from trochanter to tarsus: I–III-Leg: I: 0,1, 1, 1, 0, II: 0, I, I, 1, 0, III: 0, 1, 1,3, 0.). II/III- Leg-1 each with rather long seta which longer than seta on I-Leg-1. Solenidia on I/II-Leg-4 located distally, solenidion on I–III-Leg-3 a little displaced to the middle of these segments. Acantoid seta situated distally on tarsi of legs I and II. Central claws of all legs thicker than lateral claws and bearing two subapical teeth, claws of III-Legs ( Fig. 14 ) a little large than claws of I/II-Legs ( Fig. 13 ).

FIGURE 9. Arrenurus regulator , larva: idiosoma, fragment of ventral view, modified after Thor (1925).

Measurements (n=7). Dorsal plate L 190–210, W 175–185; setae Fch, Fp, Oi L 50–61; setae Vi L 65–70; setae Hi L 80–90; setae C1 L 64–68, setae C2 L 68–75, setae C3 L 95–105, setae C4 L 65–70; medial margins of coxae I–III L 64–71, 25–30, 48–55; urstigma D 13–15; excretory pore plate L 35–39, W 32–35; capitulum L 105–115; basal segments of che- licerae L 80–84, chela L 15–17; pedipalpal segments (P–1–5) L: 14–16, 28–32, 25–32, 14–16, 9–10; legs segments L: I–Leg-1–5: 32–39, 31–35, 35–39, 48–55, 73–77; II-Leg-1–5: 38–45, 35–42, 35–39, 50–58, 73–84; III–Leg-1–5: 40–45, 35–40, 38–42, 51–58, 83–93.

Male. Colour reddish brown, idiosoma elongate (L/W ratio 1.30–1.33), with rounded anterior margin and widest anteriorly ( Fig. 15 ). Cauda very short, somewhat truncate, and distinctly narrower than remainder idiosoma. Dorsal fur- row incomplete, terminating posteriorly on dorsum at base of cauda. Dorsal shield large, with convex anterior margin, bearing setae Oi, Hi and Sci located in anterior half and setae Li, Le, Pi and Si in posterior half. Setae and glandularia Li separated, glandularia open on relatively large tubercles. Bases of setae Pi close together medially, Le placed laterally and Si caudally. Petiole not developed. Setae Fch thicker than other idiosomal setae; trichobothria Fp, Oi and setae Pi without glandularia, other idiosomal setae associated with glandularia, Pi much shorter than other dorsal setae. Setae and glandularia Vi, Ve, Hi and Sci slightly separated, and setae and glandularia Sce strong separated. Posterior margin of cauda slightly convex, in mature specimens with posterolateral indentations. Anterolateral corners of coxal plates I–III more or less rounded, not reaching to anterior margin of idiosoma ( Fig. 16 ). Medial margin of coxal plateIV a little longer than me- dial margin of coxal plate III. Posterior coxal groups separated by moderately wide interspace. Lateral projection of coxal plates IV extending beyond lateral idiosoma margin. All coxal plates porous. In additionan, coxal plates IV with several relatively large oval cells each. Gonopore small, acetabular plates moderately wide and not reaching to lateral margins of idiosoma, two anteromedial and two posterolateral fine setae. Setae Ci located caudally. Setae and glandularia Se strong separate. Pedipalp short and stout ( Fig. 17 ): P-1 short, with a single dorsodistal setae; P-2 large, with straight or slightly convex ventral margin, two to three short, thin mediodistal and five to seven long, thick dorsal setae; P-3 relatively short, with one long, thin internal seta and comparatively short, thick external one; P-4 longer than P-2, with a stout and rather long antagonistic seta, two fine dorsodistal and two short distal setae, medial from the last bifurcate. Legs III and IV with swimming setae. IV-Leg-4 with well-developed distoventral spur bearing five to six long setae ( Fig. 18 ). Claws of leg I–III with long pointed external clawlet and short obtuse internal clawlet ( Fig. 19 ); claws of leg IV with two subequal pointed clawlets ( Fig. 20 ); claw lamella with convex ventral margin in all claws. Measurements (n=5). Idiosoma L 975– 1140, W 775–800; dorsal plate L 810–865, W 500–560; cauda L 60–75; distance between medial margins of coxal plates IV 50–75; distance between setae Oi-Oi 135–150, distance between setae Hi-Hi 350–400, distance between setae Sci- Sci 210–260, distance between setae Li 130–140, distance between setae Pi 40–50; pedipalpal segments (P-1–5) L: 30–35, 65–67, 40–45, 80–85, 30; legs segments L: I-Leg-1–6: 60–75, 75–90, 110–125, 160–175, 175–190; II-Leg-1–6: 75–90, 85–100, 125–130, 175–190, 200–215, 225–240; III-Leg-1–6: 85–100, 85–100, 120–125, 185–190, 210–225, 210–225; IV-Leg-1–6: 125–140, 145–150, 175–190, 235–250, 225–240, 200–225.

Female. Idiosoma nearly circular (L/W ratio 1.05–1.13), widest near middle, without dorsal humps or tubercles, posterolateral corners not developed ( Fig. 21 ). Dorsal furrow complete. Dorsal shield large, with convex anterior margin, a little narrowed anteriorly and posteriorly, and bears four pairs of setae (Oi, Hi, Sci, Li). Anterolateral corners of coxal plates I pointed, anterolateral corners of coxal plates II and III rounded ( Fig. 22 ). Medial margin of coxal plate III 1.5–2.0 times shorter than medial margin of coxal plate IV. Posterior coxal groups separated by moderately wide interspace. Lateral projection of coxal plates IV not reaching to idiosoma lateral margin. Ornament of all coxal plates as in the male. Genital flaps elongate (L/W ratio 1.93– 2.3) without patches, width of gonopore and distance between coxal plates IV nearly equal in size. Acetabular plates short, broad, with numerous minute acetabula, three anteromedial setae and three posteromedial setae each.

Measurements (n=2). Idiosoma L 1370–1500, W 1310–1340; dorsal plate L 1125–1250, W 935–975; distance be- tween setae Oi-Oi 225–250, distance between setae Hi-Hi 560–625, distance between setae Sci- Sci 500–565, distance between setae Li 310–325, distance between setae Pi 40–50, distance between posterior coxal groups 85–120; genital field W 700–775; genital flap L 150–165, W 75–85; pedipalpal segments (P-1–5) L: 37–38, 85–115, 55–65, 87–100, 37–38; legs segments L: I-Leg-1–6: 75–90, 85–100, 125–150, 160–200, 165–200, 175–215; II-Leg-1–6: 75–90, 125–140, 135–190, 185–265, 210–250, 225–230; III-Leg-1–5: 95–100, 110–125, 150–165, 220–240, 245–255, 235–250; IV-Leg- 1–6: 150–165, 160–190, 200–225, 260–300, 235–300, 250–290.

Differential diagnosis. The new species is similar to species of the Arrenurus regulator group which including two the European species: A. (Truncaturus) regulator Thor, 1899 and A. (Truncaturus) viktorovi ( Tuzovskij, 1976) and to two North American species: A. (Truncaturus) rufopyriformis Habeeb, 1954 and A. (Truncaturus) lacrimatus Cook, 1955 . The males of Arrenurus regulator -group are characterized by a very short cauda. Arrenurus lacrimatus and A. viktorovi are known from the males only ( Cook 1955, Mullen 1976 and Tuzovskij 1976, respectively). The larva is known only for A. regulator ( Thor 1925) . Distinctions between adults of the named species are presented in a key.

Figures

FIGURES 1–8. Arrenurus chukotkaensis sp. n., larva: 1, dorsal plate; 2, 9, idiosoma ventral view; 3–5, excretory pore plate; 6, cheli- cera, dorsal view; 7—chela, lateral view; 8, pedipalp. Scale bar: 1, 2, 3–5, 6 = 50 μm, 7, 8 = 20 μm.

FIGURES 10–14. Arrenurus chukotkaensis sp. n., larva: 10, leg I; 11, leg II; 12, leg III; 13, claws of leg I; 14, claws of leg III. Scale bars: 10–12 = 50 μm, 13–14 = 20 μm.

FIGURES 15–16. Arrenurus chukotkaensis sp. n., male: 15, dorsal view (holotype); 16, ventral view (holotype). Scale bar: 13–14 = 200 μm.

FIGURES 17–20. Arrenurus chukotkaensis sp. n., male: 17, pedipalp (holotype); 18, IV-Leg-4–6 (paratype); 19, claws of leg I (para- type); 20, claws of leg IV (paratype). Scale bars: 17 = 50 μm, 18=100 μm, 19–20 = 20 μm.

FIGURES 21–22. Arrenurus chukotkaensis sp. n., female: 21, dorsal view; 22, ventral view. Scale bar: 21–22 = 200 μm.