Hydrodroma, C.L.Koch, 1837

Gerecke, Reinhard, 2020, The early derivative water mites (Acari: Hydrachnidia, superfamilies Eylaoidea, Hydrachnoidea and Hydryphantoidea) of Madagascar, Zootaxa 4727 (1), pp. 1-77 : 28

Hydrodroma sp. inc. near amoenoderma

Material examined: MD 122b, 22.10.2001 Maromandia (Majunga), R Manongarivo, 60 m, macrophytes (0/1/5), Ac 1252 – 1253.

Description: Colour unknown. Integument structure as described for H. amoenoderma , setae numbers of coxae and legs within the variability range of that species.

Female: Idiosoma L/W 1250/1125; Cx-I+II, 300/290; Cx-III+IV, 340/310, posterolateral apodemes long, subparallel to median axis; genital plate 275/140, genital field with 220 pairs of acetabula (11 per transect) and 45 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 280/70 (2.8); I-L-5, 250/68 (4.6); II-L-4, 280/70 (4.0); II-L-5, 320/60 (5.3); III-L-4, 270/70 (3.9); III-L-5, 325/60 (5.4); IV-L-4, 350/65 (5.4); IV-L-5 damaged on both sides. Mouthparts: Gnathosoma L 240; chelicera L 355, L/H 4.9, basal segment/claw L ratio 4.1; palp total L 520; L/H (ratio) P-1, 58/70 (0.8); P-2, 95/73 (1.3); P-3, 48/63 (0.8); P-4, 230/45 (5.1); P-5, 90/20 (4.5); L ratio P- 2/P-4, 0.4, P-4/P-5, 2.6.

Remarks: This female, found together with five deutonymphs, is in agreement with the principal diagnostic features of H. amoenoderma (integument structure, shape and setation of coxae, swimming setae), but differs in by far larger genital plates bearing many more acetabula. Furthermore, leg segments are stouter than in all measured specimens of H. amoenoderma . This is probably an undescribed species; more specimens should be studied in order to define its diagnostic features.