Hydryphantes planus Thon, 1899

Tuzovskij, Petr V., 2014, Larval morphology of Hydryphantes clypeatus Thor, 1899, H. dispar Schaub, 1888 and H. planus Thon, 1899 (Acari, Hydrachnidia: Hydryphantidae), Zootaxa 3869 (2), pp. 131-142 : 138-141

Hydryphantes planus Thon, 1899

( Figs 32–45 )

Material examined. Larvae (n = 8) were reared from a single female collected in a sedge bog near village Postyltsevo, Nekouz District, Yaroslavl Province 19 June 1974, leg. P.V. Tuzovskij. The duration of the embryonic period was 14 days.

Diagnosis. Larva. Distance between bases of trichobothria Oi larger than their length; all dorsal hysterosomal setae subequal; excretory pore plate usually as long as wide or slightly longer than wide; urstigma longer than wide; posterior margin of coxal plate II straight; P-5 with short solenidion; I-Leg-4 solenidion shorter than eupathidium, II-Leg-4 solenidion longer than eupathidium; I–II-Leg-5 with subequal solenidia; I-Leg-6 de = ds.

Description. Larva. Colour red. Anterior pair of platelets triangular or oval, trichobothria Fp long and well extending to posterior margin of dorsal plate; seta Fch thick and half the length of Fp ( Fig. 32 ). Posterior plate anteriorly narrow posteriorly widening; median eye rather large and situated between setae Vi; setae Vi thick, longer than Fch; Oi short, distance between Oi-Oi larger than their length. Other dorsal setae (Oe, Hi, He, Sci, Sce, Li, Le and Si) thick and subequal.

Coxal plates II triangular without setae, coxal plates I and III more or less trapezoidal and rounded medially ( Fig. 33 ); all coxal setae relatively short and subequal. Urstigma oval, longer than wide. Setae Se, Ci, Pi and Pe subequal and slightly longer and thicker than both pairs of anal setae.

Excretory pore plate small, usually longer than wide ( Figs 34–35 ), excretory pore located near posterior plate margin. Bases of setae Ae situated near middle of excretory pore plate.

Chelicera ( Fig. 36 ) with large basal segment and small stylet. Basal segment with rather wide strips, stylet strong, without apical teeth.

Pedipalps stout ( Fig. 37 ): P-1 short and without seta; P-2 large with convex dorsal margin and single dorsal setae proximally to middle of segment; P-3 with two subequal setae (proximal and distal); P-4 with three thin nearly subequal setae, claw large, dorsodistally bifurcate, with unequal clawlets; P-5 small, with a single, short solenidion and seven setae, five long and, thick, two short and thin.

Legs 6-segmented. Shape and arrangement of specialized setae on terminal segments as shown in Figs 38–40 . I-Leg-4 solenidion slightly shorter and thinner than eupathidium, I-Leg-5 proximal solenidia subequal, I-Leg-6 eupathidium short and situated on equal level with the solenidion basis; II-Leg-4 solenidion 2.0–2.5 times longer than eupathidium, II-Leg-5 both proximal solenidia subequal in length, II-Leg-6 solenidion in proximal, eupathidium in submedial position; III-Leg-4 proximal solenidion slightly longer than III-Leg-5 solenidion. Empodium large and crescent-shaped on all tarsi, ambulacra short and thin ( Fig. 41 ).

Measurements, n=10. Dorsal plate L 45–48, W 48–51; setae Fch L 25–29, setae Fp L 55–65, setae Vi L 37–42, setae Oi L 9–13, setae Oe, Hi, He, Sci, Sce, Li, Le and Si L 28–35; setae Ci, Se, Pi, Pe 15–19; setae Ae and Ae 8-10; distance between setae Vi-Vi 35–38, distance between setae Oi-Oi 19–20; excretory pore plate L 11–13, W 10–12; urstigma L 12–13, W 10–11; basal segments of chelicerae L 73–77, cheliceral stylet L 19–23; pedipalpal segments (P-1–5) L: 6–8, 27–29, 16–19, 19–20, 10–12; leg segments L: I-Leg-1–6: 21–23, 19–20, 16–19, 25–29, 34–38, 60–65; II-Leg-1–6: 19–23, 8–10, 12–16, 15–17, 31–33, 44–48; III-Leg-1–6: 22–24, 8–10, 15–17, 19–20, 31–33, 44–45.

Female. Integument soft, with rather short, rounded papillae. Frontal plate ( Fig. 42 ) compact, anterior margin obtuse-angled, lateral and posterior margins usually concave, anterior part wider than posterior one, posterior projections short. Median eye small and situated slightly posterior to anterior setae.

Capitulum ( Fig. 43 ) with equally convex basal part and short rostrum (base of capitulum/rostrum L ratio 7.0–8.0). Chelicera ( Fig. 44 ) rather slender, basal segment with obtuse-angled dorsal hump near middle, stylet moderate in length.

Pedipalp compact ( Fig. 45 ): P-1 with 3–4 dorsodistal setae; P-2 with 13–18 setae; P-3 with 4–7 setae; P-4 slender with three thin distal setae and a short and thick dorsodistal spine.

Measurements, n=2. Idiosoma L 1100–1500; dorsal plate L 425–440, W 385–400; genital flap L 235–250, W 110–125; genital acetabula (ac.1–ac.3) L 45–50, 30–37, 50–65; capitulum L 265–275, rostrum L 35–45, chelicera L 360–375, cheliceral stylet L 120–125; pedipalpal segments (P-1–5) L: 70–80, 115–125, 75–90, 180–200, 30–35; leg segments L: I-Leg-1–6: 80–85, 120–130, 145–155, 230–250, 250–270, 260–275; II-Leg-1–6: 100–105, 145–155, 180–190, 300–315, 360–375, 345–355; III-Leg-1–6: 100–110, 130–140, 180–190, 330–345, 370–380, 345–355; IV-Leg-1–6: 205–215, 205–220, 280–290, 430–440, 430–445, 345–355.

Remarks. Larvae attributed to H. planus by Wainstein (1980) and Biesiadka & Cichocka (1990) differ distinctly from the description given here and represent obviously two different species. On the basis of my material, I suspect that the larva described by Wainstein (1980) as H. planus is the larva of H. hellichi Thor, 1899 , a species considered as a junior synonym of H. ruber (Geer, 1778) by Di Sabatino et al. (2010) without taking in consideration the larval morphology. As larvae of H. hellichi (= H. planus after Wainstein 1980) differ well from H. ruber larvae ( Wainstein 1980, Biesiadka & Cichocka 1990), this taxon should be treated as a separate species.

The H. planus larvae described here are morphologically similar to the larvae described under this name by Biesiadka & Cichocka (1990), but there are some distinctions. The median eye in the Polish larvae is situated posterior to, not between setae Vi, and the P-3 is shorter (L = 17 µm) ( Biesiadka & Cichocka 1990). These differences suggest that the larvae described from Poland belong to a species different from H. planus —possibly, there is more diversity hidden behind this name also other taxa syononymized by Lundblad (1962) could merit to be restored as separate species.

Figures

FIGURES 32 – 33. H. planus Thon, 1899, larva: 32, dorsal view; 33, ventral view. Scale bar: 50 µm.

FIGURES 34 – 41. H. planus Thon, 1899, larva: 34 – 35, excretory pore plate; 36, chelicera, dorsal view; 37, pedipalp, ventrolateral view; 38, I-Leg- 4 – 6; 39, II-Leg- 4 – 6; 40, III-Leg- 4 – 6; 41, claws of leg III. Simple setae on I – III-Leg- 4 – 6 are not shown. Scale bars: 34 – 35, 37, 41 = 20 µm, 36, 38 – 40 = 50 µm.

FIGURES 42 – 45. H. planus Thon, 1899, female: 42, frontal plate; 43, capitulum; 44, chelicera; 45, pedipalp. Scale bars: 42 = 200 µm, 43 – 44 = 100 µm, 45 = 50 µm.