Piona inflata Sokolow, 1927

Tuzovskij, Petr V., P., ., K.,., K. O., P., ., ., P., P.,., P.,., .,. P., ., P-, -, I- & Iii- -, .., 2018, On the taxonomic status of the water mites Piona inflata Sokolow, 1927 (Acari, Hydrachnidia: Pionidae), Ecologica Montenegrina 16, pp. 42-47 : 42-46

Piona inflata Sokolow, 1927

( Figs 1-18 )

Material examined. 5 males, 15 females, Russia, Samara Province, Stavropol District, National natural Park “Samarskaya Luka”, small temporary standing waters near village Koltsovo , N 53 o 11’,13’’; E 49 o 25’44’’, April-June 1994 ; 5 males, 7 females, Yaroslavl Province, Nekouz District, small forest temporary waters in vicinity of village Pogorelka and settlement Borok , April – June 2016 -2017.

Diagnosis. Both sexes: setae Fch long, thick; P-3 with three unequal setae, these shorter than dorsal margin of segment, 9-18 pairs genital acetabula; male: medial margins of posterior coxal groups clearly separated;

P-4 with two distinct setal tubercles, lying behind each other; EC proximal chamber large, with a curving narrow proximal projection, forming 1.5 coils; I/II-Leg-5/6 strong thickened distally; I-Leg-5 with three swimming setae; female: P-4 with two distinct setal tubercles which slightly separated, all acetabula and genital setae located on plates; I-Leg-4/5 with four to six short swimming setae, IV-Leg-4/5 with six to ten long swimming setae.

Redescription. Both sexes. Color red to dark brown. Idiosoma oval, integument soft and finely striated. Dorsum with two small narrow elongate platelets ( Fig. 1 ). All dorsal setae thin and approximately equal in length, but setae Fch ( Fig. 2 ) longer and thicker than others idiosomal setae. Glandularia and setae Hv free. P-3 comparatively short, with three unequal setae, lateral seta longest but shorter than dorsal margin of segment. Excretory pore surrounded by narrow sclerotized ring (occasionally in immature specimens present anterior and posterior sclerites only).

Male. Anterior coxal groups with short apodemes, posterior coxal groups medial margins clearly separated ( Fig. 3 ). Suture line between third and fourth coxal plates incomplete obliterated medially. Genital field fused to posterior coxal plates and slightly extending beyond posterolateral projections of Cx-IV. Gonopore trapezoidal in shape and with small median incision anteromedially, genital pit deep, 9-18 acetabula and 4-5 thin setae on each side. Ejaculatory complex ( Fig. 4 ) with long proximal and comparatively short distal arms, proximal chamber large, with a curving narrow proximal projection, forming 1.5 coils ( Fig.4 ).

Chelicera ( Fig. 5 ) with large basal segment and short crescent chela. Pedipalp ( Fig. 6 ) compact: P-1 short, with single short dorsodistal seta; P-2 large, with straight or slightly convex ventral margin and five short subequal dorsal setae; P-3 with three unequal setae, all these setae shorter than dorsal margin of segment; P-4 with two distinct setal tubercles, lying behind each other, ventrodistal peg-like seta short and located on small tubercle.

I/II-Leg-5/6 strong thickened distally ( Fig. 7 ); III-Leg-5 longer than III-Leg-6 and club-shaped ( Fig. 8 ); IV-Leg-4 thick, with a deep concavity bearing numerous unequal thick setae, IV-Leg-5 narrowed in anterior two third and expanded distally, IV-Leg-6 thin straight, with three to four thick setae ( Fig. 9 ). Number of swimming setae as follow: three on I-Leg-5, three to four on I-Leg-5; three to five on II-Leg-4, four on II-Leg-5; four to five on III-Leg-5; three on IV-Leg-4 and six to eight on IV-Leg-5. Claws of tarsi III relatively large, with two subequal clawlets, claw blade with equally convex ventral margin ( Fig. 10 ). Claws of legs III asymmetrical ( Fig. 11 ): large claw with thick, long straight dorsal clawlet and a relatively short, thin slightly curved ventral clawlet; small claw with relatively long internal clawlets and comparatively short external clawlet.

Measurements (n=10). Idiosoma L 750-815; dorsal plates L 100-115, W 12-15; setae Fch 60-65; cheliceral segments L: base 185-200, chela 50-65; pedipalp segments (P-1-5) L: 37-50, 135-150, 75-80, 110-125, 55-62; leg segments L: I-Leg-1-6: 75-90, 85-100, 110-125, 160-170, 165-180, 185-190; II-Leg-1- 6: 75-90, 100-115, 125-140, 185-200, 180-190, 185-200; III-Leg- 1-6: 85-95, 100-115, 125-140, 225-240, 260-270, 185-200; IV-Leg-1-6: 135-150, 100-125, 110-125, 185-200, 200-215, 200-215.

Female. All coxal groups separated and covering about half of the ventral surface in matures specimens, anterior coxal plates with short apodemes ( Fig. 12 ). Medial margin of coxal plate IV twice longer than medial margin of coxal plate III. Posterior margin of coxal plates IV forming right or obtuse angles, apodemes moderately developed. Gonopore and acetabular plates approximately equal in length. Acetabular plates with concave medial margin, 9-16 pairs of acetabula, in anterior part narrow, usually one acetabula in width ( Figs 12 , 14-15 ), occasionally two acetabula in width ( Figs 16-17 ); posteriorly broader, with two to four acetabula in width. All acetabula and genital setae located on plates. Acetabular plates with three to six anterior, and two to three posterior genital setae.

Pedipalp compact ( Fig. 13 ): P-3 with three short unequal setae, base of lateral seta located near to middle of segment; P-4 slender than in male, both ventral setal tubercles distinct and slightly separated.

Legs thin and slender. I-Leg-4/5 with four to six short swimming setae ( Fig. 18 ). Legs II-IV with long swimming setae, with the following number: six to ten on II-Leg-4/5, seven to eight on legs III-Leg-4; seven to nine on III-Leg-5, six to ten on IV-Leg-4/5.

Measurements (n=10). Idiosoma L 1000-1500; dorsal plates L 75-115, W 11-15; setae Fch L 60-90; acetabular plates: L 185-200, W 90-130; cheliceral segments L: base 195-215, chela 60-75; pedipalp segments (P-1-5) L: 50-60, 135-150, 60-75, 125-150, 55-65; leg segments L: I-Leg-1-6: 75-90, 120-150, 150-175, 210-250, 225-265, 260-285; II-Leg-1-6: 75-100, 125-150, 160-190, 250-275, 260-300, 300-315; III-Leg-1-6: 85-100, 135-165, 160-200, 260-300, 285-315, 275-315; IV-Leg-1-6: 135-165, 150-175, 185- 215, 260-310, 275-340, 250-290.

Larva. See Wainstein (1980).

Deutonymph. See Tuzovskij (1990).

Remarks. The adults P. inflata is similar to the species of the Piona nodata – complex: P. nodata , P. laminata (Thor, 1901) and P. annulata (Thor, 1901) distinguishable in the females only (Smith et al. 2015, Gerecke et al. 2016). However, the following clear differences can be found in the morphology of males of named species. I/II-Leg-5/ 6 in the male P. inflata strong thickened distally ( Fig. 6 ), posterior coxal groups with clearly separated medial margins ( Fig. 3 ), EC proximal chamber with 1.5 coils ( Fig. 4 ); in contrast, in the males of P. laminata and P. nodata I/II-Leg-5/6 distally hardly enlarged ( Gerecke et al. 2016, Tuzovskij 2017, respectively), medial margins of posterior coxal groups touching to each other ( Viets 1936, Tuzovskij 2017, respectively), EC proximal chamber in the male P. nodata with three coils ( Tuzovskij 2017).

The male of P. inflata is similar to male of Piona annulata (Thor, 1900) and differs from it by the following characters (characters states of P. annulata are indicated in parenthesis, after Tuzovskij 2016): I-Leg-5 with three short swimming setae, Fig. 7 (with two short swimming setae), EC proximal chamber with a curving narrow proximal projection, forming 1.5 coils, Fig. 4 (single coil), III-Leg-6 small claw with comparatively long internal clawlet and short external clawlet, Fig. 11 (with subequal clawlets). The deutonymphs of P. inflata and P. annulata with three pairs of acetabula, and the deutonymph of Piona nodata with two pairs of acetabula ( Tuzovskij 1990).

Thus, the morphology of P. inflata clearly differs from that of Piona nodata , P. laminata and P. annulata and P. inflata should be treated as a separate species.

Figures

Figures 1-6. Piona inflata Sokolow, 1927, male: 1 – dorsal platelets, 2 - seta Fch, 3 – idiosoma, ventral view; 4 – ejaculatory complex, 5 - chelicera, 6 – pedipalp. Scale bars: 1, 5 = 100 μm, 2, 4, 6 = 50 μm, 3 = 200 μm.

Figures 7-11. Piona inflata Sokolow, 1927, male: 7 – I-Leg-4-6, 8 – III-Leg-4-6, 9 – IV-Leg-4-6; 10 – claw of leg I, 11 - claws of leg III. Scale bars: 7-9 = 100 μm, 10, 11 = 50 μm.

Figures 12-13. Piona inflata Sokolow, 1927, female: 12 – idiosoma, ventral view; 13 – pedipalp, lateral view. Scale bars: 12 = 200 μm, 13 = 50 μm.

Figures 14-18. Piona inflata Sokolow, 1927, female: 14–17 – acetabular plate; 18 – I-Leg-4-6. Scale bar: 14-18 = 100 μm.