(Figs 1–9)
Type series. Holotype: male, slide 2962, Asia, Russia, Chukotka, Anadyr District, Anadyr River near settlement Markovo, 4. 10. 1976, leg. P. V. Tuzovskij. Paratypes: 5 females 4. 10. 1976, 2 females and 2 males 5.10. 1976 from the same locality as the holotype.
Additional material: 3 male and 2 females, Chukotka, Anadyr District, Eropol stream (inflow of the Anadyr River) near village Chuwanskoe, 7. 12. 1978; 1 female, Magadan Province, snow valley near Magadan city, brook, 7. 06. 1982; 3 females, Magadan Province, Tenka District, brook near Neitlin mountain, 1. 07. 1982; 1 male and 1 female, Kamchatka, Ust-Kamchatsk District, brook near biostation “Raduga”, 21.08. 1983, leg. P. V. Tuzovskij.
Diagnosis. Dorsalia present, integument with wrinkled lineation, glandularia slightly developed,
genital acetabula relatively small and distinctly separated, P-2 ventrodistal projection moderately long and bearing two fine setae, P-3 ventral margin straight, longer than P-2, P-4 shorter than P-3, with proximal tubercle and peg-like seta slightly larger than posterior ones, excretory pore not sclerotized, leg claws with three clawlets.
Description. Both sexes. Colour yellow to reddish brown. Idiosoma oval and somewhat flattened. Integument with wrinkled lineation. Idiosomal chaetome typical for the family Sperchontidae (Tuzovskij 1987). Dorsum (Fig. 1) with five pairs of dorsocentralia. Two anterior pairs of dorsocentral plates (dc.1 and dc.2) located lateral to trichobothria Oi, other three pairs of dorsocentral plates (dc.3–dc.5) occupy a central position, dc.1 occasionally separated in two parts. Both pairs of trichobothria (Fp and Oi) placed on small sclerites. Glandularia slightly developed.
Anterior coxal groups with rounded medial margins and well separated, apodemes not developed (Fig. 2).
Sclerites bearing setae Hv situated near posterolateral angles of coxae II. Posterior coxal groups widely separated, medial parts of coxae III narrow; glandularia Pe open at anteromedial margin of coxae III. Setae Pi not associated with glandularia. Excretory pore without sclerotized ring, located anterior to setae Ci, s etae Si and Se posterolateral. There is one pair of ventral platelets situated laterally between setae Ci and Se. Pregenital sclerite very small, postgenital sclerite comparatively large, elongate and unsclerotized. Genital field situated between posterior coxal groups, with three pairs of subequal acetabula which are distinctly separated (Figs 3). Internal margins of genital flaps convex and cover only the second pair of acetabula completely. Each flap with 12–15 median and three to five fine lateral setae. Preginital sclerite very small, postgenital sclerite comparative large, somewhat elongate and unsclerotized.
Capitulum (Fig. 5) with moderately long rostrum, ventral margin of rostrum convex. Both pairs of hypostomal setae subequal in length. Chelicera with large basal segment, chela crescent-shaped (Fig. 6).
Pedipalp (Fig.7) stout, P-1 short and without setae; P-2 large, with six to eight stout dorsal setae, ventrodistal projecting moderately long conic and bearing two fine setae; P-3 moderately large maximum height near middle of segment, ventral margin straight longer than P-2, with three to five thick and two to four thin dorsal setae; P-4 slender and a little shorter than P-3, with several rather long dorsodistal and ventrodistal fine setae, ventral margin with two small tubercles bearing short peg-like seta each, proximal tubercle and peg-like seta a little larger than posterior ones.
Legs slender, especially posterior pair, III–IV-Leg-3–5 with several rather long dorsal plumose dorsal setae (Fig. 8). Leg claws (Fig. 9) with three unequal, pointed clawlets,`dorsal clawlet longest, dorsal and median clawlets relatively thin, ventral clawlet with broad base and shorter than the anterior ones. Claw lamella well developed with concave ventral margin.
Male. Ejaculatory complex proximal chamber large, proximal arms curved, broadest basally, tapering gradually to apex, distal arms slightly convex (Fig. 4).
Measurement(n=5). Idiosoma L 730–950; capitulum L 185–230, rostrum L 60–78; genital flap L 180–205, genital acetabula (ac.1–ac.3) L: 30–42, 42–48, 30–42; cheliceral segments: base L 185–215, chela L 65–70; pedipalp segments (P-1–5) L: 30–40, 120–145, 160–180, 135–155, 25–30; legs segments L: I-Leg-1–6: 65–75, 105– 130, 105–125, 145–180, 160–190, 160–190; II-Leg-1–6: 65–75, 110–140, 115–125, 170–205, 185–230, 180–215; III-Leg-1–6: 65–80, 110–145, 120–150, 175–220, 205–255, 185–235; IV-Leg-1–6: 120–165, 160–195, 145–180, 260–235, 245–295, 220–260.
Female. External morphology similar to male but larger, anterior genital sclerite much larger than in male.
Measurement (n=10). Idiosoma L 810–1300; genital flap L 185–215, genital acetabula (ac.1–ac.3) L: 35–54, 36–48, 36–48; capitulum L 210–245, rostrum L 70–80; cheliceral segments: base L 195–215, chela L 60–75; pedipalp segments (P-1–5) L: 32–45, 130–140, 170–190, 135–170, 27–32; legs segments: I-Leg-1–6: 65–75, 120–130, 110–115, 170–180, 195–205, 180–195; II-Leg-1–6: 65–75, 120–140, 129–130, 210–220, 220–230, 195–215; III- Leg-1–6: 65–80, 130–140, 130–150, 225–245, 250–270, 220–240; IV-Leg-1–6: 135–165, 175–205, 160–190, 310– 335, 285–310, 245–285.
Deutonymph. See Tuzovskij (1990), as Sperchon tridentatus.
Larva. See Tuzovskij (2006), as Sperchon tridentatus.
Remarks. The new species is similar to S. tridentatus and S. minor. Sperchon pesici sp. n. is similar to S. tridentatus in the structure of the genital field and coxal plates, differences between the two species are found in the following characters (character states of S. tridentatus given in parentheses, data from Sokolow 1940): integument with muscle attachment sclerites (Figs 1–2) (without muscle attachment sclerites,); P-2 distoventral projecting with two fine setae, (Fig. 7) (with three setae, Fig. 22); P-3 is stockier, maximum height near middle of segment (P-3 more slender, maximum height in proximal quarter); leg claws with three unequal clawlets, lamella ventral margin concave, Fig. 9 (leg claws with three subequal clawlets, lamella ventral margin straight, Fig. 23).
The integument in S. minor with muscle attachment sclerites, dc.1 and dc.2 unsclerotized, dc.3 fused with glandulartia Sci (Fig. 24), P-2 distoventral projecting short and without fine setae, with single thick seta near base of projection (Fig. 26), ac.2 larger than ac.1 and ac.3, all acetabula slightly separated, excretory pore (Fig. 25) sclerotized (Tuzovskij 2003).
Etymology. Named after Prof. Dr Vladimir Pešić (Montenegro).
Habitat. Running waters.
Distribution. Asia, Russia: Magadan Province, Chukotka and Kamchatka.