Piona discrepans (Koenike, 1895)

Tuzovskij, Petr V., 2019, On the systematics of the water mite Piona discrepans (Koenike, 1895) and Piona discrepaniella Tuzovskij, 1990 (Acari, Hydrachnidia, Pionidae), Zootaxa 4629 (3), pp. 397-404 : 398-400

Piona discrepans (Koenike, 1895)

( Figs 1–11 , 21–23 )

1895 Curvipes discrepans Koenike. Zoologischer Anzeiger 18: 391.

Material examined. 1 female and 9 larvae: Asia, Russia, Magadan Province, Tenka District, small lake near village Sibik-Tyellakh , 19 July 1979 ; 3 females, Europe, Russia, Yaroslavl Province, Nekouz District, pond in park of settlement Borok , 12 August 1994 . Larvae were reared in laboratory (room temperature, natural day-night conditions) from a single female, the duration of the embryonic period was 11days.

Description. Larva. Idiosoma flat, dorsal plate elongate (L/W ratio 1.58–1.85), covering almost the whole dorsum ( Fig. 1 ), bearing four pairs setae (Fch, Fp, Vi, Oi) with convex lateral margins, its anterior margin straight or slightly convex, posterior margin rounded; simple setae Fch slightly shorter than Vi, trichobothria Fp and Oi relatively long, thin and subequal in length. Setae Oe, Hi, He, Sci, Sce, Li and Si situated in soft membrane, Oe longest, Si shortest, He longer and thicker than Hi. Coxal plates ( Fig. 2 ) moderately large, first plates with short apodemes directed laterally, plates II–III with single rudimentary apodeme posterior to middle of their medial margin on each side. Setae C1 much shorter than C2; C4 shorter than C2 and C3, but longer than C1. Setae Ci very long located on small tubercles. Setae Pi and Pe nearly subequal in length. Excretory pore plate ( Figs 3–4 ) wider than long (L/W ratio 0.60–0.67) with convex anterior margin and a minute median projection; bases of setae Ai and Ae located near posterior margin of the plate, Ae slightly longer than Ai. Basal segments of chelicerae ( Fig. 5 ) fused to each other medially, expanded proximally with straight anterior margin and tapering distally; chela small, crescent-shaped. Pedipalps short and stocky ( Fig. 6 ): P–1 short and without seta; P–2 large, with a single distal seta; P–3 with very long, thick lateroproximal seta and relatively short, fine dorsodistal one; P–4 with two thin unequal setae and large bifurcated dorsodistal claw, dorsal furca much large than ventral one; P–5 small, with rather long solenidion, two long and several short simple setae. Legs 5–segmented, shape and arrangement of setae on legs segments as shown in Figs 7–9 . Total number of leg setae, excluding eupathidia, as follows (specialized setae indicated in parentheses): I– Leg-1–5: 1, 7, 5(s), 10(2s), 13(s, ac); II–Leg-1–5: 1, 7, 5(s), 11(2s), 13(s, ac); III–Leg-1–5: 1, 6, 5(s), 10(s), 11(ac). Number of thickened distal setae from trochanter to tarsus: I-Leg: 0, 1, 0, 1, 0; II–Leg: 0, 1, 2, 5, 0; III-Leg: 0, 1, 2, 5, 0. I–Leg-1with relatively short seta, II/III–Leg-1 with long seta each. Solenidion or solenidia on all legs located dorsodistally. Solenidion or solenidia on I/II–Leg-3/4 longer than solenidion on III-Leg-3–4. Acanthoid seta comparatively short, located distoventrally on tarsus of all legs. Empodial claw on tarsi of all legs shorter and thicker than lateral claws ( Figs 10–11 ).

Measurements (n=9). Dorsal plate L 225–245, W 130–155; medial edge of coxa I L 64–70, medial edges of coxae II+III L 180–190; urstigma L 16–17; excretory pore plate L 25–27, W 38–40; setae Fch L 48–50, setae Fp and Oi L 37–39, setae Vi L 52–54, L 38–42; setae Oe L 95–101; setae Hi L 60–65, setae He L75–80, setae Sci L 63–67, Sce L 65–70, setae Li L 50–55, setae Le L 45–50; setae Si L 20–23; setae Se L 65–70; setae Ci L 95–100, setae Pi L 37–40, setae Pe L 40–45; setae Ai L 32–35; setae Ae L 34–40; setae C1 L 48–52, setae C2 L 85–90, setae C3 L 90–95, setae C4 L 58–65; cheliceral segments: base L90–95, chela L 12–13; pedipalpal segments (P–1–5) L: 6–7, 38–42, 25–29, 7–8, 6–7; leg segments L: I–Leg-1–5: 30–36,30–33, 30–36, 42–45, 48–51; II–Leg-1–5: 33–37, 35–37, 42–45, 53–57, 72–78; III–Leg-1–5: 35–38, 35–42, 42–45, 51–54, 75–80.

Remarks. The larva of the present species is similar to the larva of Piona coccinea Koch, 1837 , but differs in the following characters (character states of larva P. coccinea are given in parenthesis after Wainstein 1980 and Davids & Kouwets 1987): excretory pore plate transverse, Figs 3–4 (has the form of an equipotential triangle); P-3 with two setae, P-4 dorsodistal claws bifurcated, Fig. 6 (P-3 with three setae, P-4 dorsodistal claws not bifurcated); II-Leg-3 with two, II-Leg-4 with five heavy setae, Fig. 8 , III-Leg-3 with two heavy setae, Fig. 9 (II-Leg-3/4 with single heavy seta, III-Leg-3 with three heavy setae).

Larva. Hosts unknown.

Deutonymph. See Tuzovskij 1990.

Habitat. All kinds of standing waters and lowland streams (Lundblad 1968).

Distribution. Palaearctic. Widespread in Europe ( Viets, 1956, Lundblad 1968).

Figures

FIGURES 1–2. Piona discrepans (Koenike, 1895), larva: 1, dorsal view; 2, ventral view. Scale bar: 1–2=50 μm.

FIGURES 3–11. Piona discrepans (Koenike, 1895), larva: 3–4, excretory pore plate; 5, chelicera, dorsal view; 6, pedipalp, lateral view; 7, Leg I; 8, Leg II; 9, Leg III; 10, claws of leg I; 11, claws of leg III. Scale bars: 3–5, 7–9= 50 μm; 6, 10–11= 20 μm.

FIGURES 20–21. Piona discrepans (Koenike, 1895) and Piona discrepaniella Tuzovskij, 1990, adults: 20, pedipalp of P. discrepaniella; 21, idiosoma of P. discrepans, ventral view. Scale bar: 21=50 μm, 22=200μm.

FIGURES 22–23. Piona discrepans (Koenike, 1895), male: 22, idiosoma, dorsal view; 23, idiosoma, ventral view. Scale bars: 22–23=200 μm.