Unionicola tricuspis (Koenike, 1895)

(Figs 34A–D, 35A–D)

Material examined. 3 males, 4 females: Russia, Samara Province, Stavropol District, National natural Park “Samarskaya Luka”, Gusinoe lake, July 1992; 3 females and 3 males, Yaroslavl Province, Nekouz District, Rybinsk reservoir near village Pogorelka, September–November 2013, leg. P.V. Tuzovskij. All males and females are collected free-swimming.

Diagnosis. Adults. Dorsum with two pairs of small unequal platelets; coxal plates III+IV subquadrate with straight medial margin; P-3 with long lateral seta and relatively short dorsodistal seta, P-4 with three unequal ventral tubercles, P-5 moderately long with slightly concave ventral margin; anterior genital plates of female large without subcutaneous projections; genital plates of male wide, fused to each other by anterior and posterior ends, gonopore wide; swimming setae on IV-Leg-5 and IV-Leg-6 equal in length, the last with two long, thick setae; claws of legs I thick and shorter than claws of legs II–IV, all claws sickle-shaped.

Description. Both sexes. Dorsum with two pairs of small unequal platelets (Fig. 34A), anterior platelets relatively large, elongate; posterior platelets oval or circular and considerably smaller than anterior ones.

Apodemes of first coxal group reaching or little extending beyond to anterior margin of third coxae (Fig. 34B). Coxal plates III+IV subquadrate (L/W ratio 1.05–1.2) with straight medial margin. Surface of all coxal plates with reticulations.

Genital acetabula relatively small and occupy less than half of area of each plate. Sclerites, bearing setae and glandularia Le, larger than sclerites bearing other idiosomal setae.

Pedipalps moderately long (Fig. 35A): P-2 with four (rarely five) short subequal dorsal setae, P-3 with long lateral seta and one relatively short dorsodistal seta, base of lateral seta located near middle of segment; P-4 with two unequal ventral tubercles in distal half of segment each bearing thin short seta and one ventrodistal tubercle bearing short peg-like seta, and with one thin dorsoproximal seta; P-5 moderately long with slightly concave ventral margin.

The number of distal swimming setae on IV-Leg-3–6 is as follows (Fig. 35B): one on telofemur, three on genu and on tibia; swimming setae on IV-Leg-5 and IV-Leg-6 equal in length, the last with two long, thick setae. Claws of legs I (Fig. 35C) thick, hook-like and shorter than claws of legs II–IV (Fig. 35D), all claws with short dorsal clawlet and long ventral one.

Female. Anterior genital plates large, without anterior subcutaneous accretion each; both medial spines on short and subequal; anteromedial seta on posterior plate short and thin (Fig. 34C). Posterior plates relatively small with 3–4 short, thin setae each.

Measurements (n=4). Idiosoma L 810–875; coxae III+IV L 225–250, W 205–240; anterior dorsal platelets L 50–65, W 15–20; anterior genital plates L 75–90, W 115–140; posterior genital plates L 80–100, W 100–120; pedipalpal segments (P-1–5) L: 25–35, 115–125, 53–65, 110–130, 50–55; leg segments L: I-Leg- 1–6—60 –75, 135–150, 185–200, 275–290, 175–200, 185–205; II-Leg- 1–6—60 –75, 150–165, 185–200, 285–325, 330–350, 325–340; III-Leg- 1–6—60 –75, 120–135, 150–165, 210–225, 235–250, 225–250; IV-Leg-1–6—110–140, 150–165, 210–230, 285–300, 350–365, 300–325.

Male. Genital plates (Fig. 34D) wider than long, fused to each other by anterior and posterior ends, usually with 8–9 thin setae on each side, in additional one pair of genital setae located on soft integument. Gonopore wide, oval, its width nearly equal width of one genital plate.

Measurements (n=3). Idiosoma L 650–790; coxae III+IV L 200–225, W 185–215; anterior dorsal platelets L 50–60, W 12–15; genital field L 165–190, W 210–225, gonopore W 60–90; pedipalpal segments (P-1–5) L: 23–26, 100–115, 50–55, 95–105, 45–50; leg segments L: I-Leg- 1–6—60 –75, 125–140, 160–175, 245–255, 160–170, 170–180; II-Leg- 1–6—60 –75, 135–145, 160–190, 245–260, 275–290, 275–290; III-Leg- 1–6—65 –75, 95–105, 135–150, 185–200, 210–215, 200–215; IV-Leg- 1–6—95 –100, 135–145, 180–200, 235–250, 285–315, 260–275.

Deutonymph. See Hevers (1979).

Larva. See Hevers (1980).

Habitat. Lakes, reservoirs, running waters.

Hosts. Unionidae: Anodonta cygnea Linnaeus, A. anatina Linnaeus, Unio tumidus Philipsson, U. pictorum Linnaeus (Hevers 1980) .

Distribution. Europe (Viets 1936, 1956; Lundblad 1968; Viets 1978). This species is reported from Russia for the first time.