Piona annulata (Thor, 1900)

Tuzovskij, Petr V. & .,., 2016, On the systematic of the water mite Piona annulata (Thor, 1900) (Acari, Hydrachnidia: Pionidae), Ecologica Montenegrina 6, pp. 9-14 : 9-13

Piona annulata (Thor, 1900)

( Figs. 1-13)

Material examined. 5 males and 9 females, Russia, Yaroslavl Province, Nekouz District, sedge bogs, sedgesphagnum bogs, forest ponds near settlement Borok , April-June, leg P. V. Tuzovskij .

Diagnosis. Both sexes: Dorsum with two elongate narrow plates; Fch long, thick; P-3 with three short unequal setae, lateral seta slightly longer than both other setae and situated slightly proximally to middle of segment, 11-19 pairs subequal genital acetabula; I-Leg-5 with two swimming setae; male: P-4 with two distinct setal tubercles, lying behind each other; posterior coxal group touching, but not fused medially; gonopore trapezoidal in shape, genital pit deep, ejaculatory complex proximal chamber large, with a curving narrow proximal projection, forming single coil; genital field slightly extending laterally beyond posterior projections of coxal plates IV; I/II-Leg-5/6 strong thickened distally; female: P-4 both setal tubercles small and distinctly separated; two, occasionally three, genital setae situated on small platelet between acetabular plate and anterior genital sclerite on each side.

Description. Male. Colour red. Idiosoma oval, integument soft and striated. Dorsum with two small elongate narrow platelets, ratio L/ W 5.2 -7.0 ( Fig. 1). The number and position of idiosomal setae typical for the genus Piona . All dorsal setae thin and approximately equal in length, but setae Fch ( Fig. 2) many longer than other idiosomal setae. Anterior coxal groups separated with short apodemes ( Fig. 3). Sclerites bearing setae Hv, free. Posterior coxal groups touching, but not fused medially, interspace between them sclerotized. Suture line between third and fourth coxal plates incomplete obliterated medially. Acetabular plates fused to coxal plates IV posterior margin and extending laterally beyond posterior projections of these plates. Gonopore trapezoidal in shape with small median incision anteriorly, genital pit deep, 11-19 genital acetabula, on each side. Setae Pe free. Excretory pore surrounded by narrow sclerotized ring and situated anteriorly to setae Pi and Ci. Capitulum with short anchoral process and two pairs subequal ventral setae. Ejaculatory complex ( Fig. 4) with subequal proximal and distal arms, proximal chamber large, with a curving narrow proximal projection, forming single coil.

Pedipalp ( Fig. 5) stout: P-1 short, with single short dorsodistal seta; P–2 with five short subequal dorsal setae; P–3 with three short unequal setae, lateral seta slightly longer than both other setae and situated a little proximally to middle of segment; P–4 with two distinct setal tubercles, lying behind each other; ventrodistal peg-like seta short and located on small tubercle; P–5 short, with proximal solenidion, four thin setae and four very short, thick distal spines.

I/II–Leg–5/6 strong thickened distally ( Fig. 6); III–Leg-5 long, expanded distally, III–Leg-6 comparatively short and club–shaped ( Fig. 7); IV–Leg-4 thick, with a deep concavity bearing numerous unequal spine–like setae, IV–Leg-5 narrowed in anterior two third and expanded distally, IV-Leg-6 thin straight, with three to four to thick setae ( Fig. 8). Number of swimming setae as follows: one to two on I– Leg-4, two on I–Leg-5 and II–Leg-4, three on II-Leg-5 and IV–Leg-4, five to six on III-Leg-5, seven to nine on IV–Leg-5; III-Leg-4 with two to three rudimentary swimming setae. Claws of tarsi I–II relatively large, with two subequal clawlets ( Fig. 9). Claws of legs III asymmetrical ( Fig. 10); large claw with thick, long straight dorsal clawlet and a relatively short, thin slightly curved ventral clawlet; small claw with two thick pointed subequal clawlets.

Measurements (n=5). Idiosoma L 620-750; dorsal platelets L 65-90, W 6-8; seta Fch L 42-55; genital field W 365-385; cheliceral segments L: base 150-165, chela 48-55; pedipalp segments (P–1–5) L: 30- 48, 108-140, 70-78, 108-110, 45-54; leg segments L: I–Leg-1–6: 50-72, 78-100, 95-108,125-150, 140-155, 160- 175; II–Leg-1–6: 55-78, 85-100, 100-115, 135-160, 155-180, 150-185; III–Leg-1–6: 60-78, 85-105, 95-115, 168-180, 204-230, 145-156; IV–Leg-1–6: 108-115, 90-95, 95-105, 165-175, 175-186, 160-168.

Female. Dorsum similar as in of the male. All coxal groups separated and covering about half of the ventral surface in mature specimens ( Fig. 11). Anterior coxal plates with short apodemes. Sclerites bearing setae Hv free. Medial margin of coxal plate IV 1.5-2.0 times longer than medial margin of coxal plate III. Posterior margins of coxal plates IV forming obtuse angles, apodemes slightly developed. Genital opening and acetabular plates approximately equal in length. Acetabular plates bowed, narrow, with 9-15 pairs subequal acetabula in a single row; in additional, medially to acetabular plates one or two acetabula lying free in soft integument. Each acetabular plate with single anterior and two to three posterior genital setae; in additional, two (occasionally three) genital setae situated on small platelet between acetabular plate and anterior genital sclerite on each side.

Pedipalp compact ( Fig. 12): P–3 with three short unequal setae, base of lateral seta located proximally to middle of segment; P–4 slender than in male, both setal tubercles small and distinctly separated.

Legs thin and slender. I–Leg-4 with single short swimming seta, I–Leg-5 with two (occasionally with three) short swimming setae ( Fig. 13). Legs II–IV with long swimming setae, with the following numbers: one to three on II–Leg-4, three on II–Leg-5, four on III–Leg-4, five to six on III–Leg-5, three to four on IV–Leg-4 and seven to nine on IV–Leg-5.

Measurements (n=9). Idiosoma L 900–1050; dorsal platelets L 60-70, W 10-13; seta Fch L 55-65; cheliceral segments L: base 200–215, chela 48-60; pedipalp segments (P–1–5) L: 40-50, 150-165, 78-88, 150- 165, 55-63; leg segments L: Leg-1–6: 75-80, 95-105, 120-125, 160-170, 175-190, 200-215; II–Leg-1–6: 75-85, 100-115, 125-140, 175-190, 185-215, 200-215; III–Leg-1–6: 80-90, 105-115, 125-135, 200-210, 210-240, 210-225; IV–Leg-1–6: 120-130, 125-135, 150-165, 225-240, 250-260, 195-205.

Deutonymph. See Lundblad (1927), Tuzovskij (1990).

Larva. See Wainstein (1980).

Habitat. Small temporary standing waters, adults during springtime, April – May ( Lundblad 1962, 1968). I collected mature females in June in forest bogs.

Distribution. Central and Northern Europe ( Lundblad 1962, 1968); Russia: Upper Volga ( Tuzovskij 1979).

Remaks. The adults of P. annulata is similar to Piona nodata (Müller, 1776) and differs from them by the following characters (characters states of P. nodata are indicated in parenthesis, comparison is given with specimens collected in the Yaroslavl Province): both sexes: I–Leg-5 with two, occasionally with three, swimming setae, Figs. 6, 13 (with five to nine swimming setae); male: I/II–Leg–5/6 strong expanded distally, Fig. 6 (I/II-Leg-5/6 along entire length nearly an identical thickness); proximal projection of the ejaculatory complex with single coil, Fig. 4 (with three coils); female: P-4 both setal tubercles small and distinctly separated, Fig. 12 (both setal tubercles comparatively large and lying close to each other); two, occasionally three, genital setae situated on small platelet between the acetabular plate and anterior genital sclerite on each side, Fig. 3 (all genital setae situated on the acetabular plates). The groups of genital setae anterior to genital field in the females P. annulata separated from acetabular plates ( Thor, 1901); however, as have noted Smith et al. (2015), these groups of genital setae occasionally is separately on one side and fused on the other. The groups of genital setae anterior to genital field separated from the acetabular plates in all females P. annulata collected in the Yaroslavl Province.

The males described by Lundblad (1962, p.157-160, Figs.77-79) as P. nodata probably are P. annulata .