Atractides graecus K. Viets, 1950

Tuzovskij, Petr V., 2012, Larval morphology of Atractides ildensis Tuzovskij, 2005, A. moniezi (Motaş, 1927), and A. graecus Viets, 1950 (Acari: Hydrachnidia: Hygrobatidae), Zootaxa 3393, pp. 41-52 : 49-51

Atractides graecus K. Viets, 1950

(Figs 25–34)

FIGURES 25–30. Atractides graecus Viets, 1950 , larva: 25, dorsal plate; 26, coxae I–III, ventral view; 27, seta Ci; 28, excretory pore plate; 29, chelicerae; 30, pedipalp. Scale bars: 25–27 = 50 μm, 28–30 = 20 μm.

Material examined. Larva (n = 1), Ukraine, Crimea, Yalta, Bystraya stream; single larva was collected together with female, 31 May 1974.

Diagnosis. Dorsal plate elongated (L/W ratio 2.07), with reticulated pattern consisting of elongated cells only. Coxae III indented posteromedially, tmas not developed. Setae Ci located on small, short projections (L/D ratio 1.0).

Description. Idiosoma flat, dorsal plate in unengorged larvae covering almost the whole dorsum (Fig. 25), with almost straight lateral margins, its anterior margin straight, posterior margin rounded, with elongate scale-like patterns. Simple setae on dorsal plate long and thick, anterior setae (Fch) shorter than posterior setae (Vi). Both pairs of trichobothria relatively short, thin and equal in length. Nine pairs of setae (Oe, Hi, He, Sci, Sce, Li, Le, Si, Se) situated on soft wrinkled membrane, all thin and approximately equal in length.

FIGURES 30–34. Atractides graecus Viets, 1950 , larva: 31, leg I; 32, leg II; 33, leg III; 34, claws of leg I. Scale bars: 31–33 = 50 μm; 34 = 20 μm.

Coxae III indented posteromedially (Fig. 26). Setae C1, C2 and C3 approximately equal in length and shorter than C4; tmas in posteromedial corner of coxae III not developed. All leg coxae with reticulated pattern consisting of elongated cells. Seta Ci (Fig. 27) moderately long and located on short projections (L/D ratio 1.0).

Excretory pore plate (Fig. 28) large, slightly less than twice as wide as long, rounded posteriorly, concave laterally and anteriorly, and with small protrusion anteromedially; bearing four pairs of setae (Ai, Ae, Pi, Pe). Both pairs of anal setae (Ai, Ae) usually reduced and represented only by their alveoli, setae Ai located well away from anterior margin, Ae slightly posterior to middle of excretory pore plate, flanking of excretory pore, distance between setae Ae-Ae almost twice as long as distance between setae Ai-Ai; setae Pi and Pe equal in length near anterior margin of plate.

Basal segments of chelicerae fused to each other medially, their posterior edge straight (Fig. 29). Cheliceral stylet small, crescent–shaped with single subapical tooth.

Pedipalps comparatively long (Fig. 30): P–1 very short, without setae; P–2 large with one short, thin laterodistal seta; P–3 with very long, thick lateroproximal seta and short, fine laterodistal one; P–4 with three thin setae and massive dorsodistal claw; P–5 small, with one rather long solenidion and short, thin simple setae.

Shape and arrangement of setae on legs segments as shown in Figs 31–33. Total number of leg setae, excluding eupathidia, as follows (specialized setae indicated in parentheses): I– Leg–1–5: 1, 7, 5 (s), 11 (2s), 14 (s, ac); II–Leg–1–5: 1, 7, 5 (s), 11 (2s), 14 (s, ac); III–Leg–1–5: 1, 6, 5 (s), 9 (s), 11 (ac). Seta on I–Leg–1, II–Leg–1 and III –Leg–1approximately equal in length. Solenidion on I–Leg–3 and both solenidia on I–Leg–4 subequal. Proximal solenidion on II–Leg–4 longer than distal one. Solenidion on III–Leg–3 shorter than solenidion on III–Leg–4. Solenidion on I–Leg–5 occupying dorsodistal position, solenidion on II–Leg–5 situated proximally. Acanthoid seta located distally on tarsus of all legs. Claws of all legs (Fig. 34) with fine lateral teeth.

Measurements (n=1). L of dorsal plate 185, W 90; L of setae Fch 30, L of setae Fp and Oi 25–29, L of setae Vi 45, L of setae Oe, Hi, He, Sci, Sce, Li, Le, Si and Se 19–26, L of setae Pi 16, L of setae Pe 19, L of setae C1 22, L of setae C2 22, L of setae C3 25, L of setae C4 38; L of medial edges of coxae I–III 157–162; D of urstigma 15–16; L of excretory pore plate 23, W 42; L of basal segment of chelicera 67, L of cheliceral stylet 22; L of pedipalpal segments (P–1–5): 6, 34, 19, 6, 4; L of base of setae Ci 6, distance between setae Ai–Ai 8, distance between setae Ae–Ae 16; L of legs segments: I–Leg–1–5: 29, 42, 35, 36, 46; II–Leg–1–5: 32, 38, 38, 38, 50; III–Leg–1–5: 38, 48, 42, 48, 58.

Remarks. The combination of the following characters separate larvae of A. graecus from all other species of the genus Atractides : (1) coxae III indented posteromedially (Fig. 26), (2) all nine pairs of setae are situated on the soft interscutal membrane approximately equal in length, and (3) setae Ci located on short projections. This species is found in Ukraine for the first time. In the Bystraya stream only one species of Atractides has been collected.