Hygrobates (Hygrobates) setosus Besseling, 1942

Tuzovskij, Petr V., 2017, On the systematics of the water mites Hygrobates nigromaculatus Lebert, 1879 and H. setosus Besseling, 1942 (Acari, Hydrachnidia, Hygrobatidae), Zootaxa 4277 (1), pp. 17-31 : 24-28

Hygrobates (Hygrobates) setosus Besseling, 1942

( Figs 27–52 )

Material examined 12 females, 25 males, 9 deutonymphs and 32 larvae: Russia, Yaroslavl Province, Nekouz District, cold brook near village Postyltsevo , June–August 2000, 2003, 2007 ; 1 female: Yaroslavl Province, Breitovo District, Kamenka stream near village Sit’-Pokrovskoe , 7 July 2003 ; 1 female, 2 males; West Siberia, Kemerovo Province, Prokop’evsk District, forest brook near settlement Tyrgan , 5 August, 1973. Larvae were reared from four females, the duration of the embryonic period was 9–13 days.

Diagnosis. Larva. Dorsal plate elongate (L/W ratio 1.40–1.65) with parallel lateral margins, setae Fch and Vi subequal in length, tmas on coxae III present. Setae Pe longer than Pi, number of thickened distal setae on legs segments: I-Leg: 1-1-1-0-0, II-Leg: 0-2-3-3-0, III-Leg: 0-2-4-5-0.

Larva. Description. Dorsal plate elongate (L/W ratio 1.40–1.65), in unengorged larvae covering large part of dorsum ( Fig. 30 ), acute anteriorly, with parallel lateral margins, posterior end rounded, simple setae (Fch,Vi) long, thick and subequal, trichobothria Fp and Oi short, thin. Eight pairs of setae (Oe, Hi, He, Sci, Sce, Li, Le, Si) situated in soft membrane. Setae Oe longest, Hi and Sce almost subequal in length and longer than other setae situated in the membrane.

Both of coxal groups separated ( Fig. 31 ). Coxal setae C1 longer than C2; C3 longest, located on coxae II posterolaterally, C4 longer than C1 and C2. Transverse muscle attachment scar on coxae III present. Setae Pe longer than Pi. Urstigma relatively large, oval. All coxae with reticulated patterns consisting of elongated cells. Setae Ci very long, well thickened, situated on moderately long projection. Excretory pore plate wider than long (L/W ratio 0.45–0.55), slightly convex anteriorly, “W”—shaped posteriorly and with muscle attachment scars anteriorly; excretory pore and setae Ae on the same level in the center or slightly posterior of the center of plate, bases of setae Ai located close to anterior margin; distance between bases of setae Ae–Ae two times longer than distance between Ai–Ai.

Basal segments of chelicerae fused to each other medially ( Fig. 32 ), with slightly convex lateral margins and concave anterior edges. Chela relatively small crescent–shaped, with two minute subapical teeth ( Fig. 33 ).

Pedipalps stout ( Fig. 34 ): P–1 very short, without setae; P–2 relatively large, with single dorsal seta near middle of segment; P–3 with a very long, thick lateroproximal seta and short, fine dorsoproximal seta; P–4 with two unequal setae and a massive dorsodistal claw; P–5 small, with one rather long solenidion and unequal simple setae, one of them very short.

Shape and arrangement of setae, excluding eupathidia, on legs segments as shown in Figs 35–37 . Number of thickened distal setae from trochanter to tarsus: I-Leg: 1-1-1-0-0, II-Leg: 0-2-3-3-0, III-Leg: 0-2-4-5-0. Claws of legs III ( Fig. 39 ) larger than claws of legs I and II ( Fig. 38 ).

Measurements (n=10). Dorsal plate L 250–275, W 170–180; setae Fch, Vi, Hi, He L 60–70, setae Fp and Oi L 20–25, setae Oe L 80–85; setae Sci L 75–80; setae Sce, Li, Le, Se L 48–55; setae Si L 25–32, setae Ci L 205–225, setae Pi L 32–35, setae Pe L 38–42, setae C1 L 50–58, setae C-2 38–42, setae C3 L 90–96, setae C4 L 73–80; medial margins of coxae I–III L 180–185; hypostomal bay L 44–48; urstigma L 19–22; excretory pore plate L 42– 52, W 92–102; capitulum L 76–84; basal segments of chelicerae L 76–77, W 38–42, chela L 13–16; pedipalpal segments (P–1–5) L: 3–4, 28–32, 16–19, 6–10, 5–6; legs segments L: I–Leg-1–5: 31–33, 35–39, 35–37, 39–42, 48–52; II–Leg-1–5: 32–38, 38–42, 35–40, 48–55, 51–58; III–Leg-1–5: 41–45, 35–39,41–45, 58–62, 60–68.

Deutonymph. Integument soft and finely striated. Idiosoma oval and somewhat flattened dorsoventrally. Setae Fch ( Fig. 40 ) much thicker than other idiosomal setae. Anterior coxal plates with short apodemes, posteromedial margin convexity rounded ( Fig. 41 ). Coxal plate IV subtriangular in shape with rounded medial margin. Genital field with two plates, bearing two acetabula (ac-2 usually slightly larger than ac-1) and three short, thin setae each, genital sclerite small and located between the plates. Excretory pore unsclerotized and situated anteriorly to setae Pi and Ci.

Basal segment of chelicera large, with minute dorsodistal projections, chela relatively short ( Fig. 42 ).

Pedipalp moderately long ( Fig. 43 ): P-1 without setae, P-2 with one dorsoproximal seta and two dorsodistal subequal setae, ventral margin straight or slightly concave, distally forming a right angle with a few denticles covering distal 3/5 of ventral margin; P-3 with two thick dorsodistal subequal setae, ventral margin convex, with a few denticles covering distal half of segment; P-4 ventral setae on the same level, near the middle of segment.

Legs without swimming setae. Shape and arrangement of setae on terminal segments of legs I and IV as shown in Figs 44–45 . I-Leg-5 with two short subequal distoventral setae. Claws in all legs with long external clawlet and short internal one, lamella with concave ventral margin ( Fig. 46 ).

Measurements (n=9). Idiosoma L 500–570; seta Fch L35–42; coxal plates I + capitulum mL 145–155; genital plates L 60–70, W 35–42, genital acetabula (ac-1–2) L/W 24–26/30–36, 26–30/30–38; cheliceral segments L: base 125–130, chela 57–60; pedipalp segments (P–1–5) L: 18–20, 54–60, 36–48, 72–80, 23–25; legs segments L: I-Leg-1– 6: 35–42, 40–43, 54–60, 80–95, 90–105, 90–105; II-Leg-1–6: 35–42, 48–55, 60–66, 78–96, 108–120, 108–115; III- Leg-1–6: 40–45, 48–55, 65–72, 114–120, 130–140, 120–126; IV-Leg-1–6: 60–72, 58–65, 90–96, 135–145, 150– 160, 145–150.

Female. Dorsum similar to deutonymph. Setae Fch ( Fig. 47 ) thicker than others idiosomal setae. Posteromedial margin of coxal plates I rounded ( Fig. 48 ). Coxal plate IV subtriangular in shape, with a noserounded protruding medial margin.

Genital plates elongate (L/W ratio 1.90–2.65), as long as or slightly longer than gonopore, medial margin indented near the centre, with 20–29 setae each, acetabula in obtuse triangle ( Fig. 49–50 ).

Pedipalp ( Fig. 51 ) moderately long: P-1 with single dorsodistal seta; P-2 usually with six thick dorsal setae, ventral margin straight or slightly concave, distally forming a right angle, denticles covering distal 2/3 of ventral margin of P-2; P-3 with two dorsoproximal, two dorsodistal thick setae and with single seta or two thin distal setae, ventral margin straight or slightly convex, denticles covering distal 2/3 of segment; P-4 ventral setae close to each other or slightly distanced (3–6 µm) and situated near the middle of segment.

Legs slender, I-Leg-4 with two unequal relatively long distoventral setae, I-Leg-5 with two short subequal distoventral setae (Fig. 63).

Measurements (n=10). Idiosoma L 1100–1500; seta Fch L42–50; coxal plates I+capitulum mL 330–360; genital plates L 205–230, W 85–110, genital acetabula (ac-1–3) L/W 70–90/35–42, 72–90/30–42, 75–96/48–60; cheliceral segments L: base 265–290, chela 120–135; pedipalp segments (P–1–5) L: 35–42, 125–140, 90–110, 160– 170, 42–54; legs segments L: I-Leg-1–6: 75–90, 110–125, 135–165, 200–225, 210–250, 210–225; II-Leg-1–6: 85– 100, 110–140, 16 0–190, 250–275, 260–300, 235–275; III-Leg-1–6: 85–100, 135–150, 185–215, 285–315, 310– 360, 285–315; IV-Leg-1–6: 160–175, 1 60–190, 250–290, 350–390, 350–400, 310–330.

Male. Genital plate ( Fig. 27, 28 ) wider than long, anterior margin with a more or less developed knob-shaped projection, posterior margin indented, with a short bifurcated or rounded medial projection, with 17–30 pairs of setae, acetabula in a triangular position. Ejaculatory complex ( Fig. 29 ) with short anterior and comparatively long posterior arms, proximal chamber oval with convex anterior margin, a pair of rudimentary proximal horns not reaching the anterior margin of proximal chamber.

Measurements (n=10). Idiosoma L 900–1150; seta Fch L36–42; coxal plates I + capitulum mL 330–345; genital plate L 170–215, W 240–290, genital acetabula (ac-1–3) L/W 55–90/40–43, 78–90/36–42, 90–105/48–55; cheliceral segments L: base 180–250, chela 90–105; pedipalp segments (P–1–5) L: 30–35, 95–115, 65–85, 125–140, 40–48; legs segments L: I-Leg-1–6: 50–65, 80–100, 100–125, 145–170, 160–180, 145–175; II-Leg-1–6: 50–65, 85– 105, 110–140, 165–215, 190–225, 185–215; III-Leg-1–6: 65–90, 100–115, 130–165, 205–250, 240–290, 200–250; IV-Leg-1–6: 125–150, 120–150, 175–215, 235–315, 265–315, 230–270.

Remarks. The dorsal plate in larvae H. setosus from Germany is larger, L 292–300 µm ( Martin & Davids 2002) than in Yaroslavl larvae; others morphometric data without essential differences. The morphometric data of adults H. nigromaculatus , except of genital plate of male after Gerecke et al. (1960), without essential differences from known descriptions ( Martin 2010, Gerecke et al. 2016). See general remarks.

Figures

FIGURES 27 – 29. Hygobates setosus Besseling, 1942, male: 27 – 28, genital plate; 29, ejaculatory complex. Scale bars: 27 – 28, 29 = 100 µm.

FIGURES 30 – 31. Hygobates setosus Besseling, 1942, larva: 30, dorsal view; 31, ventral view. Scale bar: 100 µm.

FIGURES 32 – 39. Hygobates setosus Besseling, 1942, larva: 32, chelicerae, dorsal view; 33, chela, lateral view; 34, pedipalp, lateral view; 35, Leg I; 36, Leg II; 37, Leg III; 38, claws of leg I; 39, claws of leg III. Scale bars: 32, 35 – 37 = 50 µm, 33, 34, 38 – 39 = 20 µm.

FIGURES 40 – 46. Hygobates setosus Besseling, 1942, deutonymph: 40, seta Fch; 41, idiosoma, ventral view; 42, chelicera, lateral view; 43, pedipalp, lateral view; 44, I-Leg- 4 – 6; 45, IV-Leg- 4 – 6; 46, claw. Scale bars: 40, 42, 43, 44 = 50 µm, 41, 45 = 100 µm, 46 = 20 µm.

FIGURES 47 – 52. Hygobates setosus Besseling, 1942, female: 47, seta Fch; 48, coxal plates I – IV, ventral view; 49 – 50, genital field; 51, pedipalp, lateral view; 52, I-Leg- 4 – 6. Scale bars: 47, 49, 50, 52 = 100 µm, 48 = 200 µm, 51 = 50 µm.