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 : 22-23

Hydrodroma sp. inc. near lasioderma

Fig. 15 i – m

Material examined: MD 061, 05.09.2001 Tsimelahy (Tulear), ‘piscine naturelle’, 200 m, (0/1/1) slide mounted, Ac 1256 – 1257.

Description: (female, male unknown): Colour unknown. Integumental papillae more than twice as long as basally wide ( Fig. 15 k-m). Lateral eyes lens diameter anterior 55, posterior 40, separation not measurable. Medial margin Cx-I with very inconspicuous projections near setal bases ( Fig. 15 i ), at distal tip a bundle of 9 strong setae. Groups of similar setae in lower numbers at anterior and posterior edge of Cx-II and Cx-III. Posterior margin of Cx- IV with 11 setae in a single row; posterolateral apodeme very short (as in H. perreptans ). Swimming setae (anterior/ posterior) II-L-5, 0/0; III-L-4, 0/3; III-L-5, 0/2; IV-L-4, 1/4; IV-L-5, 0/2. Leg claw length (all legs) 33-35; L ratio claw/I-IV-L-5, 11 – 16 %. Leg segments slender (e.g., L/H ratio I-L-5, 4.6; II-L-5, 5.9; III-L-5, 6.1; IV-L-5, 7.2).

Measurements: Idiosoma L/W 1000/875; Cx-I+II, 255/170; Cx-III+IV, 255/230; genital plate 185/60, genital field with 35 pairs of acetabula (4 per transect) and 35 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 163/53 (3.1); I-L-5, 218/48 (4.6); II-L-4, 245/55 (4.5); II-L-5, 280/48 (5.9); III-L-4, 230/50 (4.6); III-L-5, 273/45 (6.1); IV-L-4, 325/58 (5.7); IV-L-5, 325/45 (7.2). Mouthparts: Gnathosoma L 190; chelicera L 250, L/H 5.0, basal segment/claw L ratio 4.0; palp total L 383; L/H (ratio) P-1, 40/53 (0.8); P-2, 63/48 (1.3); P-3, 43/43 (1.0); P-4, 165/33 (5.1); P-5, 73/14 (5.3); L ratio P-2/P-4, 0.4, P-4/P-5, 2.3.

Remarks: This female specimen, found along with a deutonymph, does not fit in the diagnosis of any other species treated here, presenting a mix of characters of H. lasioderma (integument papillae long and pointed, swimming setae number low, in total only 12 on the legs of each side) and H. mesembrina sp. nov. (leg segments slender and with relatively short claws, acetabula number rather low, see below). Possibly an undescribed species, but more material is necessary for a better definition.

Habitat: In a pool of a stream at low elevation.

Distribution: Only a single record from the southernmost part of Madagascar. From the same stream, also H. megalonyx is recorded.

Figures

FIGURE 15. Family Hydrodromidae, genus Hydrodroma. a.–d. H. amoenoderma, female (MD 151); a. Cx-I+II; b.–d. integument papillae in various views. e.–h. H. poseidon; e. Cx-I+II; f.–h. integument papillae in various views. i.–m. H. sp. inc. nr. lasioderma (MD 061); i. Cx-I+II; k.–m. integument papillae in various views.