Neoacarus hibernicus Halbert, 1944

Martin, Peter, 2016, Larval morphology of benthic and interstitial water mites (Acari: Hydrachnidia) from a Luxembourgian stream, Zootaxa 4139 (4), pp. 451-480 : 472-473

Neoacarus hibernicus Halbert, 1944

Material examined. Larvae which were attached to chironomid hosts, measurements refer to 5 larvae if not otherwise indicated.

Diagnosis. Habitus of the idiosoma rounded ( Fig. 12 A). L idiosoma 218–242 (228), W 201–211 (206). Dorsal idiosoma ( Fig. 12 A): In most cases (engorged specimens?) gnathosoma not visible or only tips of the chelicera and palps. Dp large, covering the entire dorsal idiosoma, and rounded, only slightly longer than wide. Dp bearing 4 pairs of setae, another two pairs (Hu and Mp1) displaced ventrally. L Dp 206–218 (212), W 186–203 (193), L eye capsule 17–18 (18), Mp2-Amdp (n=3) 56–62 (59), Mp1-Mp1 57–61 (59), Mp2-Mp2 116–123 (119), Lp1-Lp1 48– 54 (52), Lp2-Lp2 114–121 (116), Mp1-Lp1 6–8 (6), Mp2-Lp 2 24–27 (26), Mp1-Mp2 55–58 (56), Lp1-Lp2 36–40 (39), Mp 1 18–20 (19), Mp 2 17–20 (19), Lp 1 22–24 (23), Lp2 34–37 (36), Hu 35–36 (36), Mh1 34–34 (34), Mh2 34–40 (37), Mh3 33–39 (36), Mh 4 30–34 (31), Lh 1 31–33 (31), Lh 2 30–32 (31), Lh 3 27–30 (28). Ventral idiosoma ( Fig. 12 B–C): Expp subtriangular with truncated angles; E1 and E2 very short and pin-like, Exp displaced posteriorly ( Fig. 12 C). Two pairs of transverse muscle attachment scars present, the anterior ones may be remnants of the separation between CXII and CXIII. Setae V1 and V2 approached to mediodistal edges of CX3; V1 displaced far anteriorly, setae V2 thickened and slightly pinnate. Common median L of both CXI (max. L) (n=5) 62–65 (64), max. W CXI 29–32 (30), median common L CXII+ III 79 –89 (83), C1-C2 33–36 (34), C1-Mmcp 14– 16 (16), C4-Pmcp 64–69 (66), C4-Mmcp 35–38 (36), C1-C4 51–56 (54), C1 45–52 (48), C2 51–57 (54), C3 65–69 (67), C4 58–61 (60); median L Expp 10–12 (11), max. W 12–13 (13), E1-E1 3–5 (4), E2-E2 8–9 (8), V 1 16–22 (20), V 2 13–17 (16), V3 39 –52 (44), V4 165–191 (180), V1-V 1 10–13 (11), V2-V 2 23–32 (26), V1-V 2 7–11 (8).

Gnathosoma: ventral L base 56–62 (60), ventral W 40–44 (43), seta C3 44–47 (46), C5 43–48 (45), claw 11–12 (12).

Legs: Leg I ( Fig. 13 A): total L 124–159 (134), L IL-1 (1se) 24–28 (25), IL-2 (7se) 17–24 (19), IL-3 (4se, 1so, 1eu) 18–27 (20), IL-4 (9se, 2so, 1eu) 27–35 (29), IL-5 (12se, 1so, 2eu) 37–46 (40), H IL- 1 18–19 (19), IL- 2 18–19 (18), IL- 3 18–19 (19), IL- 4 17–19 (19), IL- 5 14–16 (15). Leg II ( Fig. 13 B): total L 147–156 (151), L IIL-1 (1se) 23–26 (24), IIL-2 (7se) 22–23 (23), IIL-3 (4se, 1so, 1eu) 24–26 (25), IIL-4 (9se, 2so, 1eu) 32–34 (33), IIL-5 (12se, 1so, 2eu) 46–48 (47), H IIL- 1 18–19 (19), IIL- 2 18–19 (19), IIL- 3 19–19 (19), IIL- 4 19–20 (20), IIL- 5 15–16 (16). Leg III ( Fig. 13 C): total L 131–163 (153), L IIIL-1 (1se) 25–28 (26), IIIL-2 (6se) 18–25 (23), IIIL-3 (4se, 1so) 19– 27 (25), IIIL-4 (9se, 1so) 29–36 (34), IIIL-5 (10se, 1eu) 39–48 (45), H IIIL- 1 17–18 (18), IIIL- 2 18–19 (19), IIIL- 3 18–19 (19), IIIL- 4 17–19 (18), IIIL-5 1 5–16 (16).

Remarks. The larva of the only European Neoacarus species, N. hibernicus , was formerly unknown. During a long-term study on the life cycle of N. hibernicus Gledhill (1969) found no larvae in the hyporheic interstitial zone in any season. Thus, he concluded that a reduction of larval parasitism may be possible. The larva described here resembles the only described North American larva of Neoacarus occidentalis ( Smith 1983) but apart from the general slightly smaller size of the North American species, examples of some remarkable differences can be observed (in parentheses N. occidentalis ): In N. hibernicus the gnathosoma is less distinctly displaced ventrally, CXII are not separated from CXIII (separated), V1 and V2 are heteromorphic (homomorphic).

For the differences to the species in the related family Athienemanniidae , see below.

Figures

FIGURE 12. Neoacarus hibernicus, larva. A. dorsal idiosoma, B. ventral idiosoma, C. area of excretory pore plate. Scale bars: A, B 100 µm, C 50 µm.

FIGURE 13. Neoacarus hibernicus, larva. A. IL, B. IIL, C. IIIL. Scale bar: 50 µm.