Ljania macilenta Koenike, 1908

Martin, Peter, 2016, Larval morphology of benthic and interstitial water mites (Acari: Hydrachnidia) from a Luxembourgian stream, Zootaxa 4139 (4), pp. 451-480 : 469-471

Ljania macilenta Koenike, 1908

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

Description. Habitus of the idiosoma moderately elongated ( Fig. 10 A), larva only a little more narrowed anteriorly than posteriorly. L idiosoma 225–244 (235), W 162–169 (166). Dorsal idiosoma ( Fig. 10 A): Dp large and alveolar, L Dp 218–237 (228), W 136–145 (141), L eye capsule (n=4) 16–19 (18), Mp2-Amdp (n=2) 33–34 (33), Mp1-Mp1 50–51 (50), Mp2-Mp2 46–48 (47), Lp1-Lp1 36–37 (37), Lp2-Lp2 79–82 (80), Mp1-Lp 1 10–11 (10), Mp2-Lp 2 19–19 (19), Mp1-Mp 2 17–18 (18), Lp1-Lp 2 31–33 (32), Mp 1 13–18 (16), Mp 2 17–17 (17), Lp 1 27–28 (27), Lp2 98–104 (101), Hu 46–50 (48), Mh1 99–102 (100), Mh2 89–98 (94), Mh3 61–65 (63), Mh4 52–56 (54), Lh1 84–85 (84), Lh2 41–46 (44), Lh3 36–36 (36). Ventral idiosoma ( Fig. 10 B): Expp strip-like and slightly incised posteriorly; E1 and E2 relatively long, located posteriorly side by side. Exp located porsteriorly on Expp. CXI bearing a small tip anteriorly. Median L CXI (n=5) 50–62 (59), max. W CXI 97–106 (102), common L of both CXII+III 104–123 (114), max. L CXII+III 123–138 (130), C1-C2 50–55 (52), C1-Mmcp 12–14 (14), C4-Pmcp (distal) 97–109 (102), C1-C4 58–64 (60), C1 56–60 (59), C2 60–78 (70), C3 90–113 (106), C4 94–109 (103); median L Expp 5–9 (7), max. W 36–41 (40), E1- E1 6 –9 (7), E2- E 2 18 –22 (21), E1- E 2 6 –10 (8), E 1 16 –27 (23), E 2 18 –25 (22), setae V1 located between distal margin of CXIII and anterior margin of Expp, V1 reaching posterior margin of idiosoma, L 27–33 (31), V 2 26–30 (28), V3 32 –36 (33), V4 (without projecting base) 155–169 (162), max. L of urstigma 11–12 (11). Gnathosoma: ventral L of base 62–75 (69), max. W (near insertion of palps) 61–67 (65), ventral L chela 14–16 (15), claw 18–21 (20), L long seta PIII 75–108 (93), L long medial seta PV 62–65 (64), L long lateral seta PV 64–69 (66).

Legs: Leg length distinctly increasing from L1-LIII. Leg I ( Fig. 11 A–B): total L 158–172 (165), L IL-1 (1se) 22–26 (24), IL-2 (7se) 25–28 (26), IL-3 (4se, 1so, 1eu) 29–32 (31), IL-4 (9se, 2so, 1eu) 36–37 (36), IL-5 (12se, 1so, 2eu) 47–49 (48), H IL- 1 14–16 (15), IL- 2 14–15 (15), IL- 3 13–14 (14), IL- 4 14–14 (14), IL- 5 12–12 (12). Leg II ( Fig. 11 C–D): total L 176–193 (183), L IIL-1 (1se) 24–26 (25), IIL-2 (7se) 26–32 (28), IIL-3 (4se, 1so, 1eu) 31– 34 (32), IIL-4 (9se, 2so, 1eu) 43–45 (44), IIL-5 (12se, 1so, 2eu) 52–57 (54), H IIL- 1 15–16 (16), IIL- 2 15–15 (15), IIL- 3 14–15 (15), IIL- 4 14–15 (15), IIL- 5 12–13 (13). Leg III ( Fig. 11 , E–F): total L 20 6–221 (213), L IIIL-1 (1se) 27–31 (28), IIIL-2 (6se) 33–34 (33), IIIL-3 (4se, 1so) 36–37 (37), IIIL-4 (9se, 1so) 53–56 (54), IIIL-5 (10se, 1eu) 59–63 (61), H IIIL- 1 13–15 (14), IIIL- 2 13–14 (14), IIIL- 3 13–14 (14), IIIL- 4 14–14 (14), IIIL- 5 12–16 (13). Leg claws consisting of one short empodium and two slightly longer ambulacra ( Fig. 11 B), all with one median tooth and two lateral teeth of comparable length.

Remarks. The larva of Ljania macilenta was previously unknown. The general morphology is similar to that of the related L. bipapillata (see Martin 2000) but there are some remarkable differences. The most striking is the difference in the shape of the Expp: large and wide posterior intended in L. bipapillata and small, thin and strip-like in L. macilenta . Interestingly, in both species the setae insertion and the Exp are located at the posterior margin of the Expp. Generally, the larva of L. macilenta is a little bit larger than its relative; this is reflected e.g. by the larger and wider Dp ( L. macilenta: L Dp 218–237, W 136–145, L. bipapillata : L 213–225, W 105–110).

Nowadays, three Ljania species are accepted in Europe ( Gerecke 2014). Apart from the two species found here, Ljania longissima Schwoerbel, 1962 is known only to exist in the Austrian Alps and the larva is still unknown.

Figures

FIGURE 10. Ljania macilenta, larva. A. dorsal idiosoma, B. ventral idiosoma. Scale bar: 100 µm.

FIGURE 11. Ljania macilenta, larva. Setation of L- 5 only visible in IL and detail figures. A. IL- 1 – 4, B. IL- 5, C. IIL, D. IIL- 5, E. IIIL, F. IIIL- 5, Scale bars: A, B, D, F 50 µm, C, E 100 µm.