Forelia brevipes (Neuman, 1880)

Tuzovskij, Petr V., 2019, Larval morphology of the water mite Forelia brevipes (Neuman, 1880) (Acari: Hydrachnidia: Pionidae), Zootaxa 4550 (3), pp. 433-438 : 433-436

Forelia brevipes (Neuman, 1880) ( Figs 1–17 )

Material examined. Larvae (n =7) were reared from single female collected in litoral zone of Rybinsk reservoir near settlement Borok (58 o 4’13’’36 N, 38 o 24’20’’83 E), Nekouz District, Yaroslavl Province, Russia, Europe, 19 July 2001.The duration of the embryonic period was 11 days.

Larva. Description. Idiosoma flat, dorsal plate in unengorged larvae covering the whole dorsum ( Fig. 1 ), with convex lateral margins, its anterior margin straight, posterior margin rounded. Dorsal plate large elongate (L/W ratio 1.42–1.50) and bearing two pairs of simple setae (Fch, Vi) and two pairs of trichobothria (Fp and Oi), simple setae slightly longer and thicker than trichobothria, Fch longer than Fp, both pairs of trichobothria thin, equal in length. Six pairs of setae (Oe, Hi, He, Sci, Sce, Li) situated in soft integument: Oe longest, He much longer than Hi, Sci and Sce subequal in length, Li much shorter than other setae situated on the soft integument.

Coxal plates ( Fig. 2 ) moderately large and elongate, first pair of plates with short apodemes directed laterally, plates II–III with a rudimentary apodeme on each side. Setae C1 relatively short and extending beyond bases setae of C4, C2– C4 subequal in length, the last setae scarcely not reaching posterior margin of the coxal plates III. Well-developed tmas,

situated in posteromedial corner of coxa III on each side, each tmas with short furca directed posteromedially. Setae Ci very long, located on small tubercles, Si short, Pi and Pe subequal in length. Excretory pore plate ( Figs 3–4 ) wider than long (L/W ratio 0.70–0.78), excretory pore located near posterior margin of plate between setae Ae, distance between bases of setae Ae–Ae two times longer than distance between Ai–Ai. Coxal plates and dorsal shield with reticulations.

Capitulum ( Fig. 5 ) with rather broad base and comparatively narrow rostrum, anterior hypostomal setae longer and thinner than posterior ones. Basal segments of chelicerae ( Fig. 6 ) fused to each other medially, longer than wide, expanded proximally and tapering distally. Chela small crescent–shaped and pointed ( Fig. 7 ).

Pedipalps very short and stocky ( Fig. 8 ): P–1 short and without seta; P–2 relatively large, with single relatively short, thin dorsodistal seta; P–3 with a very long, thick lateroproximal seta and relatively short, thin dorsodistal seta; P–4 short, with two thin lateral setae and massive hook-like dorsodistal claw; P–5 small, with one short solenidion, two long and five relatively short, thin simple setae.

Legs 5-segmented. Shape and arrangement of setae on legs segments as shown in Figs 9–11 . Total number of setae on legs I–III except for eupathidia as follows (presence and number of sensilla shown in parentheses): I-Leg-1–5: 1, 7, 5(s), 10(2s), 13(s, ac); II-Leg-1–5: 1, 7, 5(s), 11(2s), 13(s, ac); III-Leg-1–5: 1, 6, 5(s), 10(s), 11(ac). Number of heavy setae from trochanter to tarsus: I–Leg: 0, 1, 1, 1, 0; II–Leg: 0, 1, 2, 3, 0; III–Leg: 0, 1, 2, 3, 0. Solenidion on I/II-Leg-3 and both solenidia on I/II-Leg-4 located distally, solenidion on II-Leg-5 and solenidion on III-Leg-3/4 located in spaces between the middle and distal end of these segments. Claws of legs I and II ( Fig. 11 ) smaller than claws of legs III ( Fig. 12 ).

Measurements, n=7. Dorsal plate L 260–270, W 175–185; setae Fch L 55–60, Fp and Oi L 30–35, Vi L 50–55, Oe L 85–95, Hi L 45–50, He L 60–65, Sci L 35–40, Sce L 45–50; Li L 28–30, Le L 35–40, Si L 20–25, Se L 55–60, Ci L 125– 135, Pi and Pe L 40–45, C1 L 60–65, C2 L 85–90, C3 L 90–95, C4 L 80–85; medial edge of coxa I L 70–73, medial edge of coxae II+III L 105–115; excretory pore plate L 20–23, W 28–32; capitulum L 80–84; cheliceral segments L: base 70– 74, chela L 15–17; pedipalpal segments (P–1–5) L: 6–7, 25–27, 20–23, 6–8, 6–8; legs segments L: I–Leg-1–5: 32–35, 25–27, 29–32, 38–42, 44–48; II–Leg-1–5: 35–38, 25–29, 32–36, 48–50, 70–75; III–Leg-1–5: 35–40, 32–36, 35–39, 57– 60, 76–80.

Remarks. The larva of the present species is similar to larva of F. samarica . However, the following clear differences can be found in the morphology of larva of F. brevipes (character states of larva F. samarica are given in parenthesis after Tuzovskij 1997, respectively): tmas furcate, Fig. 2 (tmas not furcate, Fig. 17 ); P-4 with two thin setae, Fig. 8 (with three thin setae); dorsal plate large, L 260–270 µm, W 175–185 µm (relatively small, L 230–240 µm, W 145–160 µm); II/III-Leg-5 long, L 70–75 µm and 76–80 µm, respectively (comparatively short, L 65–70 µm and 65–75 µm, respectively).

Figures

FIGURES 1–2. Forelia brevipes (Neuman, 1880), larva: 1, dorsal view; 2, ventral view. Scale bar: 50 µm.

FIGURES 3–9. Forelia brevipes (Neuman, 1880), larva: 3-4, excretory pore plate; 5, capitulum, ventral view; 6, chelicera, dorsal view; 7, chela, lateral view; 8, pedipalp, lateral view; 9, leg I. Scale bars: 5–7, 9 = 20 µm.

FIGURES 10–13. Forelia brevipes (Neuman, 1880), larva: 10, leg II; 11, leg III; 12, claws of leg I; 13, claws of leg III. Scale bars: 10–13 = 20 µm.

FIGURES 14–15. Forelia liliacea, larva: 14, II-Leg-3–5; 15, III-Leg-3–5. Scale bar: 20 µm.

FIGURES 16–17. Forelia larvae, ventral view: 16, F. liliacea; 17, F. samarica. Scale bar: 50 µm.