Hygrobates fluviatilis (Ström, 1768)

Tuzovskij, Petr V., ., ., ., H., H., H., H., H., ., H., H., ., . & H.,. H., 2018, Larval morphology of the water mite Hygrobates fluviatilis (Ström, 1768) (Acari, Hydrachnidia, Hygrobatidae), Ecologica Montenegrina 18, pp. 110-114 : 111-113

Hygrobates fluviatilis (Ström, 1768)

( Figs 1-11 )

Material examined. Adult mites are collected by the author in streams of Samara and Yaroslavl Provinces , both located in the European part of Russia. Larvae of Hygrobates fluviatilis were reared by the author from six females: 2 females and 9 larvae from Samara Province, National natural Park “ Samara Luka”, Kuibyshev reservoir near village Koltsovo; 4 females and 32 larvae from Yaroslavl Province, Nekouz District, Ild stream near village Mar’ino. To obtain larvae, water mites were maintained in the laboratory (room temperature, natural day-night conditions). Each mature female was placed in a separate glass cylinder (10- 15 mm in diameter and 15 mm in height). The duration of the embryonic period was 9-12 days .

Diagnosis. Larva. Dosal plate elongate (L/W ratio 1.55-1.70) with slightly convex lateral margin, tmas on coxae III present, II-Leg-5 solenidion located proximally, setae Pi and Pe equal in length, number of thickened distal setae from trochanter to tarsus on legs segments:

I: 1-1-1-0-0, II: 0-2-2-1-0, III: 0-2-4-2-0.

Larva. Idiosoma flat. Dorsal plate elongate (L/W ratio 1.55–1.70), in unengorged larvae covering almost the whole dorsum, with slightly convex lateral margin, simple setae long and thick, but setae Fch much shorter than Vi, trichobothria Fp, Oi short, thin and equal in length ( Fig. 1 ). Seven pairs of setae (Oe, Hi, He, Sci, Sce, Li, Si) situated in the soft membrane laterally of the dorsal plate; Hi longest, Li shortest, Hi, He and Sci nearly subequal in length and longer than other posterior setae situated in the membrane. Surface of dorsal plate with elongate cell-shaped reticulation.

Both pairs of coxal setae (C1 and C2) short, thin and equal in length; lateral setae (C3) slightly shorter than medial setae (C4) ( Fig. 2 ). Transverse muscle attachment scar on coxa III present anteriorly to setae Pe. Urstigma relatively large and oval. Excretory pore plate large and broad (L/W ratio 0.32–0.40), slightly convex or nearly straight anteriorly, with muscle attachment scars anteriorly; excretory pore located posterior to bases of setae Ae. Anal setae (Ai, Ae) reduced and represent in form of alveoli only, distance between setae Ai-Ai shorter than distance between setae Ae-Ae. Setae Pi and Pe short, thin and equal in length. Setae Ci very long, inserted on long projections. Surface of coxal plates with elongate cell-shaped reticulation.

Capitulum ( Fig. 3 ) elongate, with relatively wide base and narrow rostrum, anterior hypostomal setae much longer than posterior ones.

Basal segments of chelicerae fused to each other medially ( Fig. 4 ), with straight or slightly convex lateral margins. Chela relatively small and crescent–shaped, with two small subapical teeth ( Fig. 5 ).

Pedipalps stout ( Fig. 6 ): P–1 very short, without setae; P–2 relatively large, with one single short dorsodistal seta; P–3 with a very long, thick lateroproximal seta and a short dorsodistal seta; P–4 with long lateral and short dorsal seta and a massive dorsodistal claw; P–5 small, with one rather long solenidion and six unequal simple setae, one of them very short.

Legs five-segmented. Shape and arrangement of setae, excluding eupathidia, as shown in Figs 7-9 . Number of thickened setae from trochanter to tarsus: I–Leg: 1-1-1-0-0; II–Leg: 0-2-2-1-0; III–Leg: 0-2-4-2- 0. Solenidion on I/II-Leg-3 and both solenidia on I/II-Leg-4 located distally, distal solenidion on II-Leg-3 much longer than both solenidia on II-Leg-4; solenidion on I-Leg-5 located distally, and solenidion on II- Leg-5 located proximally. Claws of legs I and II ( Fig. 10 ) smaller than claws of leg III ( Fig. 11 ).

Measurements (n=10). Dorsal plate L 260–275, W 160–170; setae Fch L 48-58; setae Vi L 125-145; setae Fp and Oi L 24-26; setae Hi, Sci L 83-95; setae Oe L 75–87; setae He L 80-85; setae Sce L 48-58; setae Li L 44-48, setae Le L 55-61; setae Si L 64-67; setae Se L 39-48, setae Ci L 175–195, setae Pi and Pe L 35- 39, setae C1 and C2 L 48-55, setae C3 L 67-74, setae C4 L 96-125; medial margins of coxae I–III L 160- 175; gnathosomal bay L 48-58; urstigma L 19-20; excretory pore plate L 41–45, W 105–128; capitulum L 95-103; basal segments of chelicerae L 85–90, chela L 19-23; pedipalpal segments (P–1–5) L: 4-6, 34-37, 16-22, 6-7, 4-5; leg segments L: I–Leg-1–5: 32-35, 38-45, 41-45, 49-52, 54-61; II–Leg-1–5: 35-39, 37-40, 41-45, 54-58, 64-68; III–Leg-1–5: 41-48, 44-48, 44-48, 60-65, 67-77.

Remarks. The larva of Hygrobates fluviatilis is similar to larva of H. arenarius . The larvae of H. arenarius are characterized by the following features (see Martin 2016, in parentheses: characters of H. fluviatilis ): the excretory pore located posterior to setae Ae, Fig. 2 (excretory pore centrally located between setae Ae), the surface of dorsal plate and coxal plates with well elongate cell-shaped reticulations, Figs 1-2 , respectively (surface of dorsal plate and coxal plates with not elongate cell-shaped reticulations), II-Leg-5 solendion located proximally, Fig. 8 (II-Leg-5 solendion located distally).

Figures

Figures 1–2. Hygrobates fluviatilis, larva: 1- dorsal view, 2- ventral view. Scale bar: 50 μm.

Figures 3–6. Hygrobates fluviatilis, larva: 3- capitulum, ventral view; 4 - chelicera, dorsal view, 5 – chela, lateral view, 6 - pedipalp. Scale bars: 3-4 = 50 μm, 5-6 = 20 μm.

Figures 7–11. Hygrobates fluviatilis, larva: 7 - leg I, 8 - leg II, 9 - leg III, 10 - claws of leg I, 11 - claws of leg III. Scale bars: 7-9 = 50 μm, 10-11 = 20 μm.