Hygrobates fluviatilis (Ström, 1768), Strom, 1768

Martin, Peter, 2016, Larval morphology of benthic and interstitial water mites (Acari: Hydrachnidia) from a Luxembourgian stream, Zootaxa 4139 (4), pp. 451-480 : 460-463

Hygrobates fluviatilis (Ström, 1768)

Material examined. larvae reared from females from the stream Osterau in Northern Germany (see Martin & Speth 1996), measurements refer to 5 larvae.

Description. Habitus of the idiosoma moderately elongated ( Fig. 4 A), larva only a little more narrowed anteriorly than posteriorly. L dorsal idiosoma ( Fig. 4 A) 282–303 (292), W 192–207 (202). Dp large, egg-shaped and alveolar, covering a large part of dorsal idiosoma, L Dp 276–300 (284), W 171–198 (182), Mp2-Amdp 40–46 (43), Mp1-Mp1 62–68 (65), Mp2- Mp2 49–59 (54), Lp1-Lp1 46–49 (48), Lp2-Lp2 74–79 (76), Mp1-Lp 1 12–14 (13), Mp2-Lp 2 17–22 (19), Mp1-Mp 2 25–29 (27), Lp1-Lp 2 24–28 (26), Mp 1 14–18 (17), Mp 2 8–14 (13), Lp1 58– 66 (62), Lp2 115–130 (122), Hu 85–107 (97), Mh1 94–112 (102), Mh2 82–103 (88), Mh3 67–77 (73), Mh4 60–71 (65), Lh1 82–89 (85), Lh2 59–65 (62), Lh3 46–55 (51). Ventral idiosoma ( Fig. 4 B): In most specimens, Expp distinctly incised posteriorly; E1 and E2 very short and pin-like. Common median L of both CXI-III 177–186 (181), half W CXI-III 96–108 (100), C1-C2 36–43 (40), C1-Mmcp 24–29 (26), C4-Pmcp 113–121 (116), C1-C4 54–61 (58), C1 32–38 (34), C 2 29–43 (36), C3 64–82 (73), C4 64–82 (73); L Expp 43–47 (45), W 107–115 (111), E1- E 1 10 –14 (12), E2- E 2 24 –31 (28), E1 1 –2 (2), E2 1 –2 (2), setae V1 often approaching the anterior margin of Expp, V1 34 –38 (36), V2 lying far distally on Expp, V2 34 –44 (38), V3 44 –52 (48), V4 (without projecting base) 129–195 (164), L of projecting base of V 4 21–27 (24), anterior margin of Expp-Exp 23–24 (24). Gnathosoma ( Fig. 4 D): lateral L of base 108–112 (109), ventral W 49–58 (53), chelicera ( Fig. 4 E) 89–94 (90), chela 18–20 (19), palp Fig. 4 C): L PII 34–40 (37), W 26–31 (29), L PIII 16–19 (18), W 23–28 (25), long seta PIII L 101–107 (104), claw L 14–18 (17).

Legs: Leg length increasing from L1 to L3. All three claws relatively long and thin, Lateral and medial claws provided with two subapical additional teeth ( Fig. 5 E). Leg I ( Fig. 5 A–B): total L 232–252 (243), L IL-1 (1se) 29– 35 (32), IL-2 (7se) 43–46 (44), IL-3 (4se, 1so, 1eu) 44–49 (47), IL-4 (9se, 2so, 1eu) 54–56 (55), IL-5 (12se, 1so, 1eu) 61–66 (65), H IL- 1 20–22 (21), IL- 2 19–20 (20), IL- 3 19–20 (19), IL- 4 19–22 (20), IL- 5 18–20 (19). Leg II ( Fig. 5 C–D): total L 253–276 (263), L IIL-1 (1se) 34–38 (36), IIL-2 (7se) 41–44 (42), IIL-3 (4se, 1so, 1eu) 44–48 (46), IIL-4 (9se, 2so, 1eu) 60–67 (63), IIL-5 (12se, 1so, 2eu) 74–78 (77), H IIL- 1 20–22 (21), IIL- 2 19–20 (20), IIL- 3 19–20 (19), IIL- 4 19–20 (20), IIL- 5 20–22 (21). Leg III ( Fig. 5 E–F): total L 296–313 (302), L IIIL-1 (1se) 46–48 (47), IIIL-2 (6se) 44–48 (46), IIIL-3 (4se, 1so) 52–54 (52), IIIL-4 (9se, 1so) 71–73 (72), IIIL-5 (9se, 1eu) 84–90 (86), H IIIL- 1 19–20 (20), IIIL-2 1 9–19 (19), IIIL- 3 19–20 (20), IIIL- 4 19–20 (20), IIIL-5 1 6–17 (16).

Remarks. The larva was already roughly described by Ullrich (1976), Martin (2000), Müller (2015) and in more detail by Wainstein (1980). Because of the poor availability of Wainstein’s Russian publication, the larva was re-described here.

The species is not present in the stream investigated but is probably the most common species of European streams and rivers and seen as one of the most robust species in lotic environments (e.g. Gerecke & Schwoerbel 1991). The description of the larva here may be helpful to identify other hosts of the species which was supposed to be chironomids by Gerecke & Martin (2006) and confirmed by Müller (2015).

Figures

FIGURE 4. Hygrobates fluviatilis, larva. A. dorsal idiosoma, B. ventral idiosoma, C. palpus, D. ventral gnathosomal base, E. chelicerae ventral. Scale bars: A, B 100 µm, C, D, E 50 µm.

FIGURE 5. Hygrobates fluviatilis, larva. Setation of L 5 only visible in detail figures., A. IL, B. IL- 5, C. IIL, D. IIL- 5, E. IIIL, F. IIIL- 5. Scale bars: A, C, E 100 µm, B, D, F 50 µm.