Hydrodroma amoenoderma, Gerecke, 2020

Gerecke, Reinhard, 2020, The early derivative water mites (Acari: Hydrachnidia, superfamilies Eylaoidea, Hydrachnoidea and Hydryphantoidea) of Madagascar, Zootaxa 4727 (1), pp. 1-77 : 26-28

Hydrodroma amoenoderma sp. nov.

Figs 13 d – e, 14 a – c

Type series: Holotype ♂, MNHN Ac 1236, MD 047, 25.08.2001 Betroka (Tulear), right affl. of R Mangoky NE of the village, ponds near aqueduct, 830 m, slide mounted. Paratypes: same site and date, (0/1/0) slide mounted, Ac 1237; MD 049, 26.08.2001 Betroka (Tulear), spring stream near right affl. of R Mangoky NE village, 850 m, (1/1/2) slide mounted, Ac 1238-1239; (2/2/0) in liquid, Ac 1418; MD 077, 13.09.2001 F. Dauphin (Tulear), Mandena (QMM area), ditch at right border of R Amendano, 10 m, (1/0/0) slide mounted, Ac 1241; MD 097, 26.09.2001 Ranohira (Fianarantsoa), right affl. of R Ihazofotsy ca. 3 km upstr. ‘Isalo Ranch’, 750 m, (2/1/0) slide mounted, Ac 1242 – 1244; (2/2/0) in liquid, Ac 1419; MD 099a, 26.09.2001 Ranohira (Fianarantsoa), left affl. of the stream flowing to R Ihazofotsy upstr. ‘Isalo Ranch’, 780 m, pool & riffle, (0/2/1) slide mounted, Ac 1245 – 1246; (0/7/0) in liquid, Ac 1420; MD 151, 13.11.2001 Sambava (Antsiranana), stream in vanilla plantations ca. 1 km W from the town, 10 m, (1/1/0) slide mounted, Ac 1247 – 1249; (9/6/0) in liquid, Ac 1421; MD 170b, 29.11.2001 Tampoketsan Ankazobe (Antananarivo), R Andranofeno Sud at bridge R.N.4, km 130, 1450 m, pool, (1/0/0) slide mounted, Ac 1251 .

Material examined: MD 049, 26.08.2001 Betroka ( Tulear ), spring stream near right affl. R Mangoky NE village, 850 m, (0/0/1) slide mounted, Ac 1240; MD 151 , 13.11.2001 Sambava (Antsiranana), stream in vanilla plantations ca. 1 km W from the town, 10 m, (0/0/3) slide mounted, Ac 1250 .

Diagnosis: Integument with larger, rounded papillae, each surrounded by a collar of six smaller, more irregular ones ( Figs 14 a, 15 b – d). Lateral eyes lens diameter anterior 30 – 60, posterior 25 – 50, distance 30 – 140. Medial margin Cx-I smooth or with very inconspicuous projections near setal bases; tip of Cx-I with 4 – 5 strong setae ( Fig. 15 a). Groups of similar setae at anterior and posterior edge of Cx-II (each 3 – 4) and Cx-III (6, resp. 2, slightly finer and shorter). Posterior margin of Cx-IV with 12 – 20 setae in a single, locally double row, posterolateral apodeme long, in general curved medially, more rarely subparallel to median axis ( Fig. 14 c). Swimming setae (anterior/posterior) II- L-5, 0/1; III-L-4, 0/7 – 19; III-L-5, 0/6 – 15; IV-L-4, 7 – 13/8 – 15; IV-L-5, 2 – 9/3 – 8. Leg claw length (all legs) 25 – 40; L ratio claw/ I – IV-L-5, 8 – 17 %. Leg segments slender (e.g., L/H ratio I-L-5, 4.5 – 6.2; II-L-5, 5.3 – 7.1; III-L-5, 5.4 – 6.8; IV-L-5, 6.0 – 8.2–see Fig. 13 d – e).

Description: Colour pale red. Genital field with a sexual dimorphism in number and density of medial genital plate setae: ♂♂: 50 – 100, ratio setae number/plate L 0.24 – 0.38, ♀♀: 28 – 48, ratio 0.15 – 0.20.

Measurements: Male: Idiosoma L/W 1000 – 1250/875 – 1080; Cx-I+II, 250 – 310/140 – 210; Cx-III+IV, 260 – 340/260 – 330; genital plate 210 – 260/95 – 110, genital field with 65 – 90 pairs of acetabula (6 – 9 per transect) and 50 – 100 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 150 – 195/48 – 63 (3.0 – 3.4); I-L-5, 195 – 255/40 – 48 (4.6 – 6.2); II-L-4, 220 – 300/50 – 65 (4.2 – 4.7); II-L-5, 243 – 335/40 – 55 (5.8 – 7.1); III-L-4, 203 – 270/50 – 63 (4.1 – 4.7); III-L-5, 253 – 320/40 – 50 (6.0 – 6.7); IV-L-4, 250 – 360/53 – 60 (4.6 – 6.3); IV-L-5, 300 – 370/40 – 50 (7.2 – 8.2). Mouthparts: Gnathosoma L 180 – 250; chelicera L 283 – 348, L/H 4.3 – 5.2, basal segment/claw L ratio 3.8 – 4.2; palp total L 405 – 488; L/H (ratio) P-1, 38 – 50/58 – 68 (0.6 – 0.8); P-2, 63 – 88/53 – 63 (1.1 – 1.5); P-3, 43 – 55/48 – 58 (0.8 – 1.0); P-4, 183 – 218/35 – 45 (4.8 – 5.4); P-5, 78 – 83/18 – 19 (4.1 – 4.7); L ratio P-2/P-4, 0.3 – 0.4, P-4/P-5, 2.3 – 2.7.

Female: Idiosoma L/W 1000 – 1250/825 – 1000; Cx-I+II, 230 – 290/140 – 270; Cx-III+IV, 250 – 320/240 – 330; genital plate 185 – 240/80 – 110, genital field with 54 – 115 pairs of acetabula (6 – 9 per transect) and 28 – 48 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 145 – 200/48 – 60 (3.0 – 3.3); I-L-5, 188 – 263/40 – 50 (4.6 – 5.3); II-L-4, 203 – 290/50 – 68 (4.1 – 4.6); II-L-5, 240 – 345/40 – 50 (5.9 – 6.9); III-L-4, 195 – 275/48 – 65 (4.1 – 4.5); III-L-5, 258 – 330/40 – 50 (6.0 – 6.8); IV-L-4, 275 – 375/50 – 65 (5.4 – 6.2); IV-L-5, 270 – 390/40 – 50 (6.0 – 7.8). Mouthparts: Gnathosoma L 180 – 240; chelicera L 273 – 370, L/H 4.4 – 4.7, basal segment/claw L ratio 3.7 – 4.0; palp total L 388 – 493; L/H (ratio) P-1, 40 – 48/55 – 68 (0.7 – 0.8); P-2, 60 – 95/53 – 63 (1.1 – 1.4); P-3, 43 – 58/45 – 58 (0.8 – 1.1); P-4, 170 – 225/38 – 45 (4.5 – 5.5); P-5, 70 – 85/16 – 19 (4.0 – 4.9); L ratio P-2/P-4, 0.3 – 0.4, P-4/P-5, 2.3 – 2.8.

Derivatio nominis: amoenus (Latin), pleasant, and derma (Greek: δέρμα), skin.

Remarks: Hydrodroma amoenoderma has many features in common with H. torrenticola (Walter, 1908) from the northern hemisphere: (1) Integument papillae of two types, larger ones (with rounded tips) surrounded by smaller ones arranged in a hexagonal pattern; (2) Cx-I with a smooth medial margin; (3) swimming setation well developed (on IV-L-5 on both surfaces), but posterior surfaces of II-L-5 bearing only one, of IV-L-5 less than 10 swimming setae; (4) claws moderately developed (8 – 14 % L penultimate segment). Hydrodroma torrenticola differs from H. amoenoderma in (1) a weaker development of the hexagonal smaller integument papillae (developed as flattened projections, not reaching 50% H of main papillae); (2) a more slender chelicera (total L/H> 5.3); (3) a stouter P-4 (variability with a slight overlap, L/H 4.1 – 4.6); (4) lower numbers of swimming setae on III-L (n posterior setae III-L-4, ♂♂ 8, ♀♀ 5 – 9, III-L-5, ♂♂ 4 – 7, ♀♀, 4 – 6). A further difference concerns the genital field: In contrast to H. amoenoderma , no distinct sexual dimorphism is found in number and density of medial genital plate setae of H. torrenticola (♂♂: 32 – 53, ratio setae number/plate L 0.13 – 0.20, ♀♀: 25 – 40, ratio 0.11 – 0.16).

Habitat: Pools of streams, mostly in open, unforested landscapes.

Distribution: Madagascar; in many parts of the island, but not found in the high mountains and in the high north.