Hydrodroma perreptans (K. Viets, 1913 )

Gerecke, Reinhard, 2020, The early derivative water mites (Acari: Hydrachnidia, superfamilies Eylaoidea, Hydrachnoidea and Hydryphantoidea) of Madagascar, Zootaxa 4727 (1), pp. 1-77 : 15-17

Hydrodroma perreptans (K. Viets, 1913)

Figs 8 , 9 a – e

Material examined: MD 063, 07.09.2001 Andohahela (Tulear), Isaka , stream exp. W 1 km N from the village, 250 m, riffle, (0/1/0) slide mounted, Ac 1280; riparian spring nearby, (1/1/0) slide mounted, Ac 1281 – 1282; MD 072 , 10.09.2001 Andohahela (Tulear), Isaka , stream crossing RIP 118 at km 34.5, 540 m, (0/1/0) in liquid, Ac 1426; MD 073 , 10.09.2001 Andohahela (Tulear), Isaka , riparian springs near stream crossing RIP 118 at km 34.5, 540 m, (1/1/0) in liquid, Ac 1427; MD 074 , 11.09.2001 Andohahela (Tulear), Isaka , stream crossing RIP 118 at km 32, 360 m, riffle, (1/1/0) slide mounted, Ac 1283 – 1284, (3/2/0) in liquid, Ac 1428; MD 155a , 17.11.2001 Joffreville (M. d’Ambre, Antsiranana), left affl. R de Manques in Reserve Fontenay , 600 m, riffle, (1/1/1) slide mounted, Ac 1285 – 1286; (2/1/0) in liquid, Ac 1429; MD 162 , 20.11.2001 Joffreville (M. d’Ambre, Antsiranana), R de Manques in Reserve Fontenay, 730 m, riffle, (0/1/0) slide mounted, Ac 1287; (1/1/1) in liquid, Ac 1430; MD 163, same stream and date, 580 m, (0/0/1) slide mounted, Ac 1288; MD 164 , 20.11.2001 Joffreville (M. d’Ambre, Antsiranana), riparian springs at R de Manques in Reserve Fontenay , 580 m, (1/0/0) slide mounted, Ac 1289; MD 181 , 23.03.2011 Joffreville (M. d’Ambre, Antsiranana), Cascade sacrèe, pool and riffle below, 1043 m, S 12°31’17’’, E 049°10’12’’, (1/0/0) in liquid, in coll. Gerecke.

Description: Colour deep red. Integument papillae longer than basally wide, basal diameter wider than interspaces, surrounded by six more or less developed, often denticle-like, elevations ( Figs 8 e , 9 c – e ). Lateral eyes with rather small lenses (diameter anterior 35 – 45, posterior 20 – 30), distance 60 – 110. Venter: Figs 8 c , 9 a – b . Medial margin Cx-I smooth or with very inconspicuous projections near setal bases. Tips of Cx-I/II with bundles of 10 – 15 densely arranged stronger setae, a bundle of similar setae at posterolateral edge of Cx-II; Cx-III laterally with two groups of long setae, at anterior, resp. posterior plate edge. Numerous finer setae arranged along the anterior and posterior margins of Cx-I (mostly in a single line), the posterior margin of Cx-II (one, medially 2 – 3 lines), and the posterior margin of Cx-III and –IV (each with 20 – 30 setae in 2 – 3 lines). Cx-IV with a short posteromedial apodeme. Leg segments not remarkably stout ( Fig. 8 a – b ). Swimming setae (anterior/posterior) II-L-5, 0/0-1; III-L-4, 0/1; III-L-5, 0/1; IV-L-4, 0/1; IV-L-5, 0/1. Leg claw length (all legs) 40 – 58, corresponding to 18 (14 – 23) % length of penultimate segment.

Measurements: Males: Idiosoma L/W 850 – 975/725 – 825; Cx-I+II, 240 – 265/170 – 180; Cx-III+IV, 240 – 280/220 – 250; genital plate 180 – 210/65 – 70, genital field with 55 – 62 pairs of acetabula (5 per transect) and 35 – 50 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 155 – 168/50 – 55 (3.0 – 3.1); I-L-5, 205 – 210/45 – 47 (4.5 – 4.6); II-L-4, 205 – 225/50 – 55 (3.9 – 4.1); II-L-5, 250 – 260/45 – 48 (5.6 – 5.8); III-L-4, 205 – 225/45 – 55 (4.0 – 4.6); III-L-5, 235 – 260/40 – 45 (5.7 – 5.9); IV-L-4, 295 – 305/50 – 60 (5.1 – 5.9); IV-L-5, 305 – 325/40 – 45 (7.1 – 7.6). Mouthparts: Gnathosoma L 180; chelicera L 250 – 260, L/H 5.6 – 6.1, basal segment/claw L ratio 4.0 – 4.1; palp total L 315 – 330; L/H (ratio) P-1, 35 – 43/50 (0.7 – 0.9); P-2, 45 – 60/45 (0.9 – 1.3); P-3, 38 – 43/40 – 45 (0.8 – 1.1); P-4, 138 – 140/33 – 38 (3.7 – 4.3); P-5, 50 – 55/14 – 15 (3.6 – 3.7); L ratio P-2/P-4, 0.3 – 0.4, P-4/P-5, 2.5 – 2.8.

Females: Idiosoma L/W 1100 – 1250/825 – 1125; Cx-I+II, 285 – 330/190 – 220; Cx-III+IV, 280 – 325/260 – 300; genital plate 195 – 220/80 – 120, genital field with 50 – 85 pairs of acetabula (6 – 8 per transect) and 28 – 44 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 175 – 205/50 – 65 (2.9 – 3.2); I-L-5, 220 – 250/45 – 53 (4.6 – 4.8); II-L-4, 230 – 268/55 – 65 (3.9 – 4.2); II-L-5, 260 – 305/45 – 55 (5.0 – 6.1); III-L-4, 230 – 265/55 – 65 (4.2 – 4.5); III-L-5, 270 – 315/45 – 50 (5.5 – 6.3); IV-L-4, 320 – 370/60 – 65 (5.3 – 5.7); IV-L-5, 300 – 435/45 – 55 (6.7 – 8.3). Mouthparts ( Fig. 8 d ): Gnathosoma L 200 – 245; chelicera L 265 – 333, L/H 4.6 – 5.5, basal segment/claw L ratio 3.6 – 4.2; palp total L 348 – 438; L/H (ratio) P-1, 40 – 43/50 – 63 (0.7 – 0.8); P-2, 60 – 80/50 – 55 (1.2 – 1.5); P-3, 40 – 55/45 – 50 (0.9 – 1.1); P-4, 150 – 170/34 – 38 (4.3 – 4.5); P-5, 55 – 60/15 – 16 (3.7 – 4.0); L ratio P-2/P-4, 0.4 – 0.5, P-4/P-5, 2.7 – 2.8.

Remarks: The specimens from Madagascar fit the original description (K. Viets 1913) and the extended diagnosis given by Gerecke (2017–based on the holotype and populations from continental Africa), except for an occasionally increased number of acetabula in the female genital field: up to 85 pairs, up to 8 in a transect line. In view of the low number of specimens available for variability studies from continental Africa, such an extension of the variability range is not surprising. All specimens have the characteristically slender palp (L/H ratio 3.9 – 4.5) that allows distinction from H. rheophila Cook, 1967 (Asia/southern Europe).

Habitat: Low order streams and spring habitats. In contrast to most species of the genus with a preference for lotic sectors; the extreme reduction of swimming setation is an adaptation to habitats of this type.

Distribution: Widely distributed in sub-Saharan Africa, but records scattered. In Madagascar, probably distributed all over the forested areas of the island, at middle altitude (250 – 730 m asl.).

Figures

FIGURE 8. Family Hydrodromidae, genus Hydrodroma, H. perreptans female (MD 063). a. III-L-4–6; b. IV-L-4–6; c. coxal and genital field (most setae given as insertion pores only); d. gnathosoma with chelicera and palp; e. integument papillae.

FIGURE 9. Family Hydrodromidae, genus Hydrodroma. a.–e. H. perreptans (MD 074a); a.–b. female and male Cx-I+II; c.–e. integument papillae in various views–note in e. the underlying hexagonal structure visible upper left; f.–k. H. megalonyx (MD 120a); f.–g. male and female Cx-I+II; h.–k. integument papillae in various views.