Oxidae K. Viets, 1926

Tuzovskij, Petr V., 2013, Larval morphology of Lebertia longiseta Bader, 1955, L. dubia Thor, 1899 and Oxus nodigerus Koenike, 1898 (Acari, Hydrachnidia: Lebertiidae, Oxidae), Zootaxa 3619 (5), pp. 569-580 : 577-580

Family Oxidae K. Viets, 1926

Genus Oxus Kramer, 1877

Oxus nodigerus Koenike, 1898 ( Figs 30–39 )

Material examined. Larvae (n = 33) were reared from six females: one female collected in a tundra pool near the village of Markovo, Anadyr District, Magadan Province, 26 June 1981; five females collected in a forest bog near the village Postyltsevo, Nekouz District, Yaroslavl Province: one female collected on 13 July 2000, two females on 21 July 2000, one female on 17 May 2005 and one female on 9 June 2006. The duration of the embryonic period was 11–15 days.

Diagnosis. Idiosoma narrow, dorsal plate elongated (L/W ratio 1.5–1.7), setae Oe, Hi, He, Sci and Sce equal in length, trichibothria Fp and Oi not branched; eye platelets with rounded posterior margins; excretory pore plate slightly longer than wide (L/W ratio 1.15–1.25); setae Ae and Ai nearly equal in length; II–Leg-4 and III–Leg-4 with two short greatly thickened setae.

Description. Idiosoma flat, dorsal plate ( Fig. 30 ) elongate (L/W ratio 1.5–1.7), narrow anteriorly, widest near bases of setae Hi. In unengorged larvae covering large part of dorsum, with convex lateral margins, its anterior margin slightly concave, rounded posteriorly. Dorsal plate bearing five pairs of setae: three pairs of simple setae (Fch, Vi, Hi) and two pairs of trichobothria (Fp, Oi). Simple setae long and thick, Hi longest, Fch shorter and thinner than Vi; both pairs of trichobothria short and thin, equal in sizes and not branched. Seven pairs of setae (Oe, He, Sci, Sce, Li, Le, Si) situated on soft wrinkled membrane: Oe longest, Si shortest.

Coxal plates large, plates II–III on each side completely fused to each other, suture line between them developed only in their lateral parts ( Fig. 31 ). Anterior coxal plates completely separated from coxal plates II and III. All coxal setae (C1–C5) approximately equal in length. Setae Ci very long, located on small tubercles and much longer than Se. Pre-anal setae relatively short, but Pe longer than Pi. All coxal plates have reticulated patterns consisting of elongated cells.

Excretory pore plate a little longer than wide, oval with more or less developed anteromedial projection ( Figs 32–33 ); anal setae (Ai, Ae) approximately equal in length, Ai located anteriorly, Ae located laterally in posterior half of plate; excretory pore placed between setae Ai and Ae near middle of plate; distance between setae Ae–Ae a little longer than distance between Ai–Ai.

Chelicerae bases partly fused to each other ( Fig. 34 ), its dorsal margins convex, ventral margins concave; cheliceral stylets relatively small, crescent–shaped without subapical teeth.

Pedipalps moderately developed ( Fig. 35 ): P–1 short and glabrous; P–2 large with a convex dorsal margin and a single dorsal setae proximally to the middle of segment; P–3 with very long, thick lateroproximal setae and a relatively short, fine dorsoproximal seta; P–4 with three subequal setae and a massive, dorsodistal claw; P–5 small, with single solenidion, one short, thin seta and six short, thick spine-like setae.

Legs 5–segmented, basifemur and telofemur of all legs fused to each other, with indistinct suture line. Shape and arrangement of setae on legs segments as shown in Figs 36–38 . Total number of leg setae, excluding eupathidia, is as follows (specialized setae given in parentheses): I–Leg-1–5: 1, 7, 5 (s), 10 (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), 9 (s), 11–12; proximal ventral setae on tarsus III sometimes absent. Number of short thickened setae from trochanter to tarsus: I–Leg: 0, 1, 1, 1, 0; II–Leg: 0, 2, 2, 2, 0; III–Leg: 0, 2, 2, 2, 0. I–Leg-1 with relatively short seta, II–Leg-1 and III–Leg-1 each with long seta. Solenidion on genu of legs I–III and tarsi I–II short; solenidia on tibia I–II relatively long and located in distal half of these segments. Solenidion on genu III and tibia III short subequal and situated in distal half of these segments. Acanthoid seta short curved and present only on tarsus I and II. Lateral claws of all legs longer and thinner than the heavy empodial claw ( Fig. 39 ), all claws are sickle shaped, empodial claw provided with a lateral spur on each side.

Measurements, n=10. L of dorsal plate 240–275, W 145–160; L of setae Fch 48–50, L of setae Fp and Oi 38–42, L of setae Vi 55 –60, L of setae Oe 100–105; L of setae Hi, He, Sci and Sce 85–105; L of setae Li and Le 80–90; L of setae Si and Se 70–80, L of setae Ci 160–175, L of setae Pi 19–23, L of setae Pe 28–32, L of setae C1 65–77, L of setae C2 70–80, L of setae C3 80–90, L of setae C4 65–80; L of setae C5 70–80; L of medial margin of coxae I 145–150, L of medial margins of coxae II–III 35 –40; L of excretory pore plate 22–26, W 17–21; L of capitulum 76–92; L of basal segments of chelicerae 65–80, L of cheliceral stylet 14–19; L of pedipalpal segments (P–1–5): 11–16, 28–35, 22–29, 9–12, 6–7; L of legs segments: I–Leg-1–5: 38–42, 41–45, 40–43, 60–66, 67–71; II–Leg-1–5: 38–42, 45–48, 44–46, 64–70, 76–80; III–Leg-1–5: 40–45, 45–48, 44–50, 67–71, 85–88.

Remarks. The larva of the present species is similar to the larva of O. magnellus Tuzovskij, 1984 , from which it is easily distinguished by the structure of the eye platelets and by the shape and sizes of the idiosomal and coxal setae. The eye platelets in the larva of O. magnellus have pointed anterior and posterior margins, trichibothria Fp and Oi are branched, the setae on P-4 are not longer than length of segment and the setae C1 are extending to bases of C4 (Tuzovskij 1984). In contrast, the eye platelets in the larva of O. nodigerus have pointed anterior margins and rounded posterior margins, the trichibothria Fp and Oi are not branched, the setae on P-4 are longer than length of segment and the setae C1 are not reaching bases of C4.

Figures

FIGURES 30 – 31. Oxus nodigerus Koenike, 1898, larva: 30, dorsal view; 31, ventral view. Scale bar: 50 μm.

FIGURES 32 – 35. Oxus nodigerus Koenike, 1898, larva: 32 – 33, excretory pore plate; 34, chelicerae, lateral view; 35, pedipalp, lateral view. Scale bar: 20 μm.

FIGURES 36 – 39. Oxus nodigerus Koenike, 1898, larva: 36, leg I; 37, leg II; 38, leg III; 39, claws of leg III. Scale bar: 20 μm.