Atractides samaricus Tuzovskij, 2004

Tuzovskij, Petr V., ., .., ., -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, ., - & P-, 2017, Larval morphology of the water mite Atractides samaricus Tuzovskij, 2004 (Acari, Hydrachnidia, Hygrobatidae), Ecologica Montenegrina 11, pp. 1-5 : 1-4

Atractides samaricus Tuzovskij, 2004

( Figs 1–11 )

Material examined. 5 larvae reared in laborarory (IBIW) from one female, Russia, Yaroslavl Province, Breitovo District, Kamenka stream near settlement Sit’-Pokrovskoe , June 2005, P. V. Tuzovskij, duration of the embryonic period was 15 days .

Diagnosis. Larva. Dorsal plate elongate (L/W ratio 1.50-1.6), with reticulated pattern consisting of elongated cells only, tmas absent, II-Leg-3 with two heavy setae, I/II-Leg-3 with long solenidion.

Larva. Idiosoma flat and elongated, dorsal shield 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 only. Simple setae on the dorsal shield 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, Sci subequal, longer and thicker than other setae situated in the membrane.

Both pairs of coxal setae (C1, C2) short, thin and equal in length ( Fig. 2 ). Lateral setae (C3) on coxae II a little longer than medial seta (C4) on coxa III. Urostigma very small and occupying lateral position on border between coxae I and II, supplied with cap. Transverse muscle attachment scar on coxa III not developed. All leg coxae with reticulated pattern consisting of elongated cells. Setae Ci very long, well thickened, on moderately elongated projections.

Excretory pore plate large and broad, L/W ratio 0.50- 0.55, with small muscle attachment scars near setae Pi ( Fig. 3 ). Both pairs of anal setae (Ai, Ae) reduced and represented in form alveoli only; Ai located moderately away from anterior margin and Ae near middle of plate, flanking posterior margin of excretory pore; distance between Ae–Ae almost twice as long as distance between Ai–Ai; setae Pi and Pe subequal in length and situated near anterior margin of excretory pore plate.

Basal segments of chelicerae fused to each other medially, their posterior edges straight ( Fig. 4 ). Chela small, crescent–shaped with single subapical tooth ( Fig. 5 ).

Palps relatively short ( Fig. 6 ): P-1very short, without setae; P-2 with one short, thin dorsodistal seta; P-3 with very long, thick proximal seta and comparatively short, thin dorsodistal one; P-4 with two rather long unequal setae and massive dorsodistal claw; P-5 small, with one rather long solenidion and short, thin simple setae.

Leg 5–segmented. Shape and arrangement of setae on leg segments as shown in Figs 7-9 . Total number of leg setae, excluding eupathids, as follows (specialized setae indicated in parenthesis): I-Leg-1–5: 1, 7, 5 (s), 11 (2s), 14 (s, ac); II-Leg-1-5: 1, 7, 5 (s), 10 (2s), 14 (s, ac); III-Leg-1-5: 1, 6, 5 (s), 10 (s), 11 (ac). Number of thickened distal setae from trochanter to tarsus: I–III-Leg: 1-1-1-1-0, II: 0-2-2-4-0, III: 0-1-4-6-0. Trochanter of legs II and III each with rather long seta. I-Leg-4 both solenidia located in distal half of segment; II-Leg-4 proximal solenidion located near middle of segment. I-Leg-5solenidion located distally, and II-Leg-5 solenidion located proximally. I/II-Leg-3 with on long solenidion each, and III-Leg-3with short solenidion. Claws of legs III ( Fig. 11 ) larger than claws of legs I and II ( Fig. 10 ).

Measurements, n = 5. Dorsal plate L 240–250, W 160–110; medial edges of coxae I–III L 147–152; urostigma L 10–11; excretory pore plate L 35–39, W 64 –77; cheliceral segments: base L 64–68, chela L 14–16; pedipalpal segments (P-1–5) L: 3-5, 32-36, 16-17, 4-6, 3-5; setae Ci L 145-160, base of seta Ci L 12– 13; legs segments L: I-Leg-1–5: 25-28, 28-32, 28-32, 35-39, 41-48; II-Leg-1–5: 25-29, 32-36, 32-36, 41-45, 48-52; III-Leg-1–5: 32-35, 32-39, 41-45, 44-48, 51-55.

Remarks. The larva Atractides samaricus is similar to A. ildensis Tuzovskij, 2004 . The presence two groups of large oval or circular cells in anterior part of dorsal shield, tmas in the posteromedial corners of coxae III, and II-Leg-3 with three heavy setae are characteristics of the larva of A. ildensis ( Tuzovskij 2012) . In contrast, in the larva A. samaricus anterior part of the dorsal shied without any groups oval or circular cells ( Fig. 1 ), tmas absent in the posteromedial corners of coxae III ( Fig. 2 ), and II-Leg-3 with two heavy setae.

The morphology of the larva described by Wainstein (1980) as A. spinipes Koch, 1837 is similar with the description of the larva A. samaricus given above. The shape and size of dorsal shield, coxal plates, chelicerae, absent tmas on the coxal plates III, and II-Leg-3 with two heavy setae are identical at both species.

Female (slide 29504-IBIW) identified under the name A. spinipes Koch, 1837 from which were the larva is reared and described ( Wainstein, 1980) is characterised by the following features: leg claws with three clawlets, III/IV-Leg-5 with two swimming setae each, and setae Ci and Pi (= Vgl-1 and Vgl-2) separated. These features are in perfect agreement with description of the adults A. samaricus ( Tuzovskij 2004) . In the adults of A. spinipes is leg claws with two clawlets, III/IV-Leg-5 without swimming setae, setae Vgl-1 fused to Vgl-2 ( Gerecke 2003, Gerecke et al. 2016). Therefore, the larva described under the name A. spinipes ( Wainstein 1980) probably refer to A. samaricus .

Figures

Figures 1-2. Atractides samaricus Tuzovskij, 2004, larva: 1- dorsal view, 2 - ventral view. Scale bar: 50 μm.

Figures 3-6. Atractides samaricus Tuzovskij, 2004, larva: 3 - excretory pore plate, 4 - chelicerae, dorsal view, 5 – chela, lateral view; 6 - pedipalp, lateral view. Scale bars: 3-4, 5-6 = 20 μm.

Figures 7-11. Atractides samaricus Tuzovskij, 2004, larva: 7 – leg I, 8 - leg II; 9 - leg III; 10 - claws of leg I; 11 - claws of leg III. Scale bars: 7-9, 10-11 = 20 μm.