Hydrodroma mesembrina, 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 : 23-24

Hydrodroma mesembrina sp. nov.

Figs 11 e – h , 12 f – i

Type series: Holotype ♀, MNHN Ac 1267, MD 151, 13.11.2001 Sambava (Antsiranana), stream in vanilla plantations ca. 1 km W from the town, 10 m. Paratypes: same site and date, (4/3/0) slide mounted, Ac 1268 – 1274; MD 077, 13.09.2001 F. Dauphin (Tulear), Mandena (QMM area), ditch at right border of R Amendano, 10 m, (0/1/0) slide mounted, Ac 1275; MD 078a2, 15.09.2001 F. Dauphin (Tulear), Mandena (QMM area), R Amendano 0.5 km upstr. road bridge, 12 m; riffle upstream, (1/3/0) slide mounted, Ac 1276 – 1279; (1/8/0) in liquid, Ac 1424; MD 078b2, same site and date, pool upstream (1/2/0) in liquid, Ac 1425.

Diagnosis: Integument with longish, slightly curved main papillae surrounded by six flat elevations ( Figs 11 f , 12 g – i ). Lateral eyes lens diameter anterior 35 – 65, posterior 25 – 55, distance 20 – 55. Medial margin Cx-I smooth or with very inconspicuous projections near setae bases; tips with 5 – 7 strong setae ( Figs 11 e , 12 f ). Groups of similar setae at anterior and posterior edge of Cx-II and (slightly finer and shorter) Cx-III. Posterior margin of Cx-IV with 17 – 18 setae in a single, slightly irregular row, posterolateral apodeme relatively stout, subparallel to the median axis. Swimming setae (anterior/posterior) II-L-5, 0/1; III-L-4, 0/6-10; III-L-5, 0/5 – 7; IV-L-4, 7 – 11/7 – 9; IV-L-5, 0/4 – 6. Leg claw length (all legs) 28 – 40 – 9 – 18 % penultimate segment. Leg segments relatively slender (e.g., L/H ratio I-L-5, 4.3 – 6.0; II-L-5, 5.5 – 6.0; III-L-5, 5.4 – 6.2; IV-L-5, 6.8 – 7.3 see Fig. 11 g – h ).

Description: Colour red. Leg claws of I – II-L relatively longer (11 – 18 % penultimate segment) than those of III – IV-L (9 – 13 %).

Measurements: Male: Idiosoma L/W 750 – 875/650 – 750; Cx-I+II, 225 – 270/145 – 170; Cx-III+IV, 240 – 290/230 – 260; genital plate 170/65, genital field with 41 – 44 pairs of acetabula (4 – 5 per transect) and 64 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 135 – 160/50 – 55 (2.7 – 3.0); I-L-5, 183 – 225/43 – 45 (4.3 – 5.0); II-L-4, 200 – 235/50 – 55 (4.0 – 4.3); II-L-5, 235 – 285/43 – 48 (5.5 – 6.0); III-L-4, 195 – 225/45 – 53 (4.1 – 4.4); III-L-5, 230 – 265/40 – 48 (5.4 – 5.7); IV-L-4, 245 – 300/45 – 53 (5.3 – 5.7); IV-L-5, 265 – 320/38 – 45 (7.0 – 7.1). Mouthparts: Gnathosoma L 170 – 195; chelicera L 235 – 273, L/H 3.9 – 4.0, basal segment/claw L ratio 3.9 – 4.7; palp total L 345 – 400; L/H (ratio) P-1, 40 – 45/48 – 55 (0.8); P-2, 58 – 70/45 – 55 (1.3); P-3, 38 – 40/41 – 48 (0.8 – 0.9); P-4, 148 – 170/30 – 38 (4.1 – 4.9); P-5, 63 – 75/14 – 15 (4.2 – 5.3); L ratio P-2/P-4, 0.4, P-4/P-5, 2.1 – 2.4.

Female: Idiosoma L/W 700 – 1000/600 – 875; Cx-I+II, 220 – 350/138 – 170; Cx-III+IV, 230 – 290/220 – 280; genital plate 160 – 180/65 – 100, genital field with 36 – 55 pairs of acetabula (4 – 6 per transect) and 28 – 38 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 138 – 168/45 – 55 (3.0 – 3.2); I-L-5, 180 – 220/40 – 45 (4.3 – 4.9); II-L-4, 203 – 240/48 – 58 (4.1 – 4.4); II-L-5, 235 – 270/40 – 45 (5.8 – 6.0); III-L-4, 195 – 225/48 – 53 (4.1 – 4.4); III-L-5, 233 – 265/40 – 45 (5.4 – 6.2); IV-L-4, 258 – 300/45 – 55 (5.4 – 5.7); IV-L-5, 270 – 315/40 – 45 (6.8 – 7.3). Mouthparts: Gnathosoma L 175 – 205; chelicera L 235 – 280, L/H 4.2 – 4.9, basal segment/claw L ratio 3.7 – 4.0; palp total L 338 – 423; L/H (ratio) P-1, 40 – 50/48 – 55 (0.8 – 0.9); P-2, 50 – 70/43 – 65 (0.8 – 1.4); P-3, 38 – 48/38 – 48 (1.0 – 1.1); P-4, 145 – 178/30 – 38 (4.6 – 4.9); P-5, 65 – 78/15 (4.3 – 5.2); L ratio P-2/P-4, 0.3 – 0.4, P-4/P-5, 2.2 – 2.4.

Derivatio nominis: mesembrinòs (Greek: μεσεμβρινός), southern.

Remarks: Hydrodroma mesembrina is similar to H. despiciens (Müller, 1776) from the northern hemisphere (data from Gerecke 2017) in the shape of integument papillae and general swimming setation of legs (II-L-5 anteriorly without, posteriorly with only one swimming seta; III/IV-L-4 – 5 with numerous swimming setae, on III-L-4 – 5 and IV-L-5 restricted to posterior, on IV-L-4 on both sides)—in setae numbers, only an inconspicuous difference is found (total 30 – 42, in H. despiciens 44 – 57; IV-L-5 with 4 – 6, in H. despiciens 7 – 10 posterior swimming setae). Furthermore, Hydrodroma despiciens differs in (1) generally major measurements of all sclerotized parts (e.g. genital plate L/W ♂♂ 189 – 250/100 – 112, ♀♀ 198 – 265/100 – 117; P-4 L ♂ & ♀ 184 – 220; IV-L-4 L ♂ & ♀ 314 – 435); (2) generally more slender leg segments (e.g., L/H ratio III-L- 5 ♂♂ 6.0 – 7.0, ♀♀ 6.3 – 7.3) and (3) relatively shorter leg claws (7 – 12 % L penultimate segment). From all previously discussed Madagascan species of the genus, H. mesembrina differs in higher swimming setae numbers and relatively shorter leg claws.

Habitat: Standing and running waters of coastal plains. At sites MD 070 and 151, the species was found coexisting with H. amoenoderma sp. nov., at MD 077 with H. amoenoderma and H. zhokhovi .

Distribution: In the extreme south and northeast of Madagascar.

Figures

FIGURE 11. Family Hydrodromidae, genus Hydrodroma. a.–d. H. lasioderma female (MD 120a); a. integument structure; b. III-L-5–6; c. IV-L-5–6; d. Cx-I+II; e.–h. H. mesembrina male (MD 151); e. coxal and genital field; f. integument papillae; g. III-L-4–6; h. IV-L-4–6.

FIGURE 12. Family Hydrodromidae, genus Hydrodroma. a.–e. H. lasioderma (MD 154b); a.–b. female and male Cx-I+II; c.–e. integument papillae in various views; f.–i. H. mesembrina (MD 151); f. female Cx-I+II; g.–i. integument papillae in various views; k.–n. H. zhokhovi female; k. Cx-I+II; l.–n. integument papillae in various views.