Atractides ildensis Tuzovskij, 2005

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 : 42-49

Atractides ildensis Tuzovskij, 2005

(Figs 1–12)

FIGURES 1–2. Atractides ildensis Tuzovskij, 2005 , larva: 1, dorsal view; 2, ventral view. Scale bar: 1–2 = 50 μm.

Material examined. Larvae (n = 34) were reared from six females collected in Il’d stream near village Mar’ino, Nekouz District, Yaroslavl Province: one female 27 June 2003, one female 7 July 2003, two females 29 July 2004, and two females 1 July 2005. The duration of the embryonic period was 10–14 days at room temperature.

Diagnosis. Dorsal plate elongated (L/W ratio 1.65–1.70), with two groups of large oval or circular cells in anterior half; tmas present; setae Ci located on moderately long projections (L/D ratio 1.3–1.5).

Description. Idiosoma flat, dorsal plate in unengorged larvae covering almost the whole dorsum (Fig. 1), with slightly convex lateral margins, its anterior margin straight, posterior margin rounded, with reticulated pattern consisting of elongated cells, and two groups of large oval or circular cells in the anterior half of the plate. Simple setae on the dorsal plate long and thick, anterior setae (Fch) shorter than posterior setae (Vi); both pairs of trichobothria short, thin and equal in length. Nine pairs of setae (Oe, Hi, He, Sci, Sce, Li, Le, Si, Se) situated in soft membrane; Oe, Hi and Sce subequal, longer and thicker than other setae situated in the membrane.

FIGURES 3–7. Atractides ildensis Tuzovskij, 2005 , larva: 3, anal plate; 4, capitulum, ventral view; 5, chelicerae, dorsal view; 6, cheliceral stylet, lateral view; 7, pedipalp, lateral view. Scale bar: 3–7 = 20 μm.

FIGURES 8–12. Atractides ildensis Tuzovskij, 2005 , larva: 8, leg I; 9, leg II; 10, leg III; 11, claws of leg I; 12, claws of leg III. Scale bar: 8–12 = 20 μm.

Both pairs of setae on coxae I (C1, C2) short, thin and equal in length. Lateral setae (C3) on coxae II and medial setae (C4) on coxae III long, thick and approximately equal in length (Fig. 2). Well developed tmas situated in posteromedial corner of coxa III on each side. All coxae with reticulated pattern consisting of elongated cells. Setae Ci very long, well thickened, on moderately long projection (L/D ratio 1.3–1.5).

Excretory pore plate large and broad, L/W ratio 0.5–0.6, more or less rounded anteriorly and posteriorly, anteriorly with muscle attachment scars (Fig. 3). Excretory pore plate setae (Ai and Ae) usually reduced and represented in form of alveoli only, setae Ai located moderately away from anterior margin and setae Ae slightly posterior to middle of plate, flanking excretory pore; distance between setae Ae-Ae almost twice as long as distance between setae Ai-Ai; Pi and setae Pe equal in length and situated near anterior margin of plate.

Capitulum (Fig. 4) elongate with relatively wide base and narrow rostrum. Basal part of capitulum longer than rostrum. Basal segments of chelicerae fused to each other medially, their posterior edges straight with small median incision (Fig. 5). Cheliceral stylet small, crescent–shaped with minute subapical tooth (Fig. 6).

Pedipalps relatively short (Fig. 7): P-1 very short, without setae and fused to P-2, suture line between these segments usually visible in young specimens; P-2 with one short, thin dorsodistal seta; P-3 with very long, thick proximal seta and short, fine dorsodistal one; P-4 with two unequal setae and massive, dorsodistal claw; P-5 small, with one rather long solenidion and short, thin simple setae.

Legs 5–segmented. Shape and arrangement of setae on legs segments as shown in Figs 8–10. 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), 10 (s), 11 (ac). II–Leg-1 and III–Leg-1each with rather long seta, with longer than seta on I-Leg-1. Solenidion on I-Leg-3, II-Leg-3 and proximal solenidion on I-Leg-4 subequal and longer than distal solenidion on I-Leg-4. Proximal solenidion on II- Leg-4 twice as long as distal solenidion. Solenidion on I-Leg-5 short and in dorsodistal position, solenidion on II- Leg-5 long and situated proximally; III-Leg-3 with short solenidion, slightly shorter than solenidion on III-Leg-4. Acanthoid seta located distally on tarsus of all legs. Claws of legs III (Fig. 11) larger than claws of legs I and II (Fig. 12). Central claw and lateral claws in all legs nearly subequal in size and with a few hair–like projections.

Measurements, n=10. L of dorsal plate 210–225, W 124–130; L of setae Fch 28–35, L of setae Fp and Oi 16–19, L of setae Vi 38 –48, L of setae Oe 57–64, L of setae Hi 57–64, L of setae He 25–32, L of setae Sci 57–64, L of setae Sce 32–39, L of setae Li 32–39, L of setae Si 22–29, L of setae Se 25–29, L of setae Le 32–39, L of setae Ci 110–130, L of setae Pi 22–26, L of setae Pe 22–26, L of setae C 1 25–32, L of setae C 2 25–32, L of setae C3 58–64, L of setae C4 64–70; L of medial edges of coxae I–III 140–150; D of urstigma 14–16; L of excretory pore plate 32–39, W 65–70; L of capitulum 76–87; L of basal segment of chelicera 54–65, L of cheliceral stylet 12–16; L of pedipalpal segments (P–1–5): 3–5, 25–30, 16–18, 4–6, 4–5; L of base of setae Ci 12–15, D of base of seta Ci 9–10; distance setae Ai–Ai 12–16, distance setae Ae–Ae 22–26; L of legs segments: I–Leg-1–5: 25–29, 31–33, 31–34, 38–42, 44–48; II–Leg–1–5: 28–32, 30–33, 32–36, 41–46, 50–55; III–Leg–1–5: 31–35, 32–38, 35–39, 44–52, 51–58.

Remarks. The presence tmas situated in the posteromedial corners of coxae III (Fig. 2) and two groups of large oval or circular cells in anterior part of dorsal plate (Fig. 1) are unique characteristics of the larva of A. ildensis and will serve to separate it from all other known species of the genus Atractides .

Atractides moniezi (Mota ş, 1927) (Figs 13–24)

Syn. Atractides virginalis Tuzovskij, 1977 ( Gerecke 2003)

Material examined. Larvae (n = 28) were reared from three mature females collected in Il’d stream near village Mar’ino, Nekouz District, Yaroslavl Province: one female 20 May 2003, one female 29 June 2004 and one female 1 June 2008. The duration of the embryonic period at room temperature was 9–13 days.

Diagnosis. Dorsal plate elongated (L/W ratio 1.90–1.95), with two groups of large oval or circular cells in anterior half and numerous very small circular cells forming a transverse group in the posterior half; tmas present; setae Ci located on very long projections (L/D ratio 2.1–2.2).

Description. Idiosoma flat, dorsal plate in unengorged larvae covering almost the whole dorsum (Fig. 13), with almost straight lateral margins, anterior margin straight, posterior margin rounded, with elongate scale-like patterns, two groups of large oval or circular cells in the anterior half and with numerous minute circular cells forming transverse group in posterior half. Simple setae on dorsal plate long and thick, anterior setae (Fch) shorter than posterior setae (Vi). Both pairs of trichobothria short, thin and equal in length. Nine pairs of setae (Oe, Hi, He, Sci, Sce, Li, Le, Si, Se) are situated in the soft membrane; setae Oe, Hi, Sce subequal, longer and thicker than other setae situated on the membrane; setae He shorter than Oe, Hi, Sce but longer and thicker than setae Sce, Li, Le, Si, Se.

FIGURES 13–14. Atractides moniezi (Motaş, 1927) , larva: 13, dorsal view; 14, ventral view. Scale bar: 1–2 = 50 μm.

Both setae on coxae I short, thin and subequal. Lateral setae (C3) on coxae II and medial setae (C4) on coxae III long, thick and approximately equal in length. Well developed tmas situated in the posteromedial corner of coxa III. All coxae with reticulated pattern consisting of elongated cells. Setae Ci very long, well thickened, located on very long projections (L/D ratio 2.1–2.2).

Excretory pore plate (Fig. 15) large, its width nearly having twice its length (L/W ratio 0.45–0.50), with convex anterior and posterior margins and small protrusion anteromedially, both pairs of anal setae (Ai, Ae) usually reduced and represented only by alveoli, setae Ai located moderately away from anterior margin, setae Ae slightly posterior to the middle of the excretory pore plate, flanking or slightly anterior to excretory pore; distance between setae Ae-Ae almost twice as long as the distance between setae Ai-Ai; setae Pi and Pe equal in length, situated near the anterior margin of the excretory pore plate.

Capitulum (Fig. 16) elongate with relatively wide base and narrow rostrum. Basal part of capitulum twice as long as rostrum. Basal segments of chelicerae fused to each other medially, their posterior edges concave (Fig. 17). Cheliceral stylet small, crescent–shaped with single subapical tooth (Fig. 18).

Pedipalps relatively short (Fig. 19): P–1 very short, without setae and fused to P–2, suture line between these segments usually visible in young specimens; P-2 large with one short, thin dorsodistal seta; P–3 with very long, thick lateroproximal seta and short, fine dorsodistal one; P–4 with two unequal setae and massive, dorsodistal claw; P–5 small, with one rather long solenidion and short, thin simple setae.

FIGURES 15–19. Atractides moniezi (Motaş, 1927) , larva: 15, anal plate; 16, capitulum, ventral view; 17, chelicerae, dorsal view; 18, cheliceral stylet, lateral view; 19, pedipalp, lateral view. Scale bar: 15–19 = 20 μm.

Shape and arrangement of the setae on legs segments as shown in Figs 20–22. 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), 10 (2s), 13 (s, ac); III–Leg–1–5: 1, 6, 5 (s), 10 (s), 11 (ac). Seta on II–Leg–1 longer than seta on I–Leg–1 but shorter than seta on III –Leg–1. Solenidion on I–Leg–3 and II–Leg–3 longer than solenidion on III–Leg–3; proximal solenidion on I–Leg–4 and II–Leg–4 subequal and slightly longer than distal solenidion on I–Leg–4 and II–Leg–4. Solenidion on I–Leg–5 short, in dorsodistal position, solenidion on II–Leg–5 long and situated proximally; solenidion on III–Leg–4 longer than solenidion on III–Leg–3. Acanthoid seta located distally on tarsus of all legs. Claws of legs III (Fig. 23) larger than claws of legs I and II (Fig. 24).

FIGURES 20–24. Atractides moniezi (Motaş, 1927) , larva: 20, leg I; 21, leg II; 22, leg III; 23, claws of leg I; 24, claws of leg III. Scale bar: 20–24 = 20 μm.

Measurements, n=10. L of dorsal plate 230–240, W 118–125; L of setae Fch 32–38, L of setae Fp and Oi 25–29, L of setae Vi 57 –65, L of setae Oe 64–74, L of setae Hi 70–80, L of setae He 32–39, L of setae Sci 70–80, L of setae Sce, Li, Le, Si, Se 28–32, L of setae Pi 19–22, L of setae Pe 22–26, L of setae C 1 22–25, L of setae C 2 22–29, L of setae C3 67–74, L of setae C4 76–80; L of medial edges of coxae I–III 157–162; D of urstigma 15–16; L of excretory pore plate 38–42, W 83–87; L of capitulum 80–87; L of basal segment of chelicera 64–68, L of cheliceral stylet 14–16; L of pedipalpal segments (P–1–5): 4–6, 25–29, 19–26, 6–7, 5–6; L of base of setae Ci 25–29, D of base of seta Ci 12–13; distance setae Ai–Ai 12–16, distance setae Ae–Ae 22–26; L of legs segments I–Leg–1–5: 22–29, 32–34, 31–33, 35–39, 35–42; II–Leg–1–5: 25–32, 29–23, 28–35, 41–45, 48–52; III–Leg-1–5: 32–39, 37–39, 38–42, 51–55, 54–61.

Remarks. The larva A. moniezi is similar to the larva A. ildensis , from which it is easily distinguishable by the structure of the dorsal shield. The posterior half of the dorsal plate in larva A. moniezi with numerous minute cells forming a transverse group (Fig. 13). In contrast, the posterior portion of the dorsal plate in larva A. ildensis without transverse group of minute cells (Fig. 1).

This species was synonymized with A. lacustris (Lundblad, 1925) by Pesic et al. (2010). Unfortunately, the authors did not give a detailed analysis of the morphology of the named species, although there is potential of morphological distinction. The setae Fch (=Dgl-1) in adults of A. lacustris are short, the posterior end of the coxal plates II+III is angular and pointed, the bases of the ventral setae divide P-4 into three unequal sectors (3:2:2), and the sword seta on P-4 inserted between ventral setae ( Gerecke 2003). In contrast, the setae Fch in female of A. moniezi are long, the posterior end of the coxal plates II+III is wide and obtuse, the bases of the ventral setae divide P-4 into three equal sectors (1:1:1), and the sword seta on P-4 is inserted near the distoventral seta ( Tuzovskij 1977, Gerecke 2003). Due to the mentioned characters I consider A. moniezi as a separate species.