Hydrodroma lasioderma, 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 : 20-22

Hydrodroma lasioderma sp. nov.

Figs 11 a – d , 12 a – e

Type series: Holotype ♂, MNHN Ac 1254, MD 154b, 17.11.2001 Joffreville (M. d’Ambre, Antsiranana), R de Manques in Reserve Fontenay, 550 m, in roots, slide mounted . Paratypes: same site and date, (0/1/1) slide mounted, Ac 1255; (1/1/0) in liquid, Ac 1422.

Diagnosis: Integument papillae strongly elongated and distally narrowed ( Figs 11 a , 12 c – e ). Posterior margin of Cx-IV with posterolateral apodeme relatively long and strong, directed medially. Swimming setae (anterior/posterior) II-L-5, 0/1; III-L-4, 0/2; III-L-5, 0/2-3; IV-L-4, 0-1/3; IV-L-5, 0/3. Leg claw length (all legs) 45 – 65 – 17 – 23 % L penultimate segment. Leg segments relatively stout (e.g., L/H ratio I-L-5, 4.0 – 4.3; II-L-5, 4.2 – 5.0; III-L-5, 4.8 – 5.2; IV-L-5, 5.4 – 5.9–see Fig. 11 b – c ).

Description: Colour red. Integumental papillae digitiform, more than two times as long as basally wide, apically rounded. Lateral eyes diameter anterior lens 50 – 65, posterior 30 – 45, distance 45 – 70. Medial margin Cx-I smooth or with very inconspicuous projections near setal bases ( Figs 11 d , 12 a – b ). Cx-I with a bundle of 13 – 15 strong and long setae at anterior tip, 8 – 11 medial and 8 – 12 posterior margin setae. Cx-II with groups of long and strong setae at anterior (11 – 13) and posterolateral edge, total number at posterior margin 17 – 29. Cx-III with 6 – 8 longer setae at distal tip, 12 – 20 at posterior margin, Cx-IV total setae number 14 – 21 (all finer and shorter), posterolateral apodeme long and strong, directed medially.

Measurements: Male (n=2, gnathosoma and its appendages n=1): Idiosoma L/W 800 – 1020/700 – 900; Cx-I+II, 240 – 270/170 – 180; Cx-III+IV, 230 – 250/240 – 260; genital plate 170 – 200/50 – 70, genital field with 40 – 50 pairs of acetabula (at maximum 4 – 5 per transect) and 30 – 35 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 150 – 168/53 – 60 (2.8 – 2.9); I-L-5, 200 – 216/50 – 52 (4.0 – 4.2); II-L-4, 200 – 210/55 – 60 (3.3 – 3.8); II-L-5, 240 – 270/50 – 54 (4.8 – 5.0); III-L-4, 208 – 216/55 – 58 (3.7 – 3.8); III-L-5, 240 – 265/50 – 54 (4.8 – 4.9); IV-L-4, 247 – 265/55 – 63 (3.9 – 4.8); IV-L-5, 270 – 314/50 – 54 (5.4 – 5.8). Mouthparts: Gnathosoma L 180; chelicera L 235, L/H 5.2, basal segment/claw L ratio 3.5; palp total L 350; L/H (ratio) P-1, 33/48 (0.7); P-2, 65/50 (1.3); P-3, 43/40 (1.1); P-4, 155/33 (4.8); P-5, 55/16 (3.4); L ratio P-2/P-4, 0.4, P-4/P-5, 2.8.

Female (n=2, gnathosoma and its appendages n=1): Idiosoma L/W 1050 – 1075 /875 – 1050; Cx-I+II, 290 – 300/200 – 230; Cx-III+IV, 275 – 310/290 – 320; genital plate 210 – 215/85 – 95, genital field with 68 – 75 pairs of acetabula (at maximum 6 per transect) and 25 – 35 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 190 – 205/63 – 70 (2.9 – 3.0); I-L-5, 230 – 250/54 – 63 (4.0 – 4.3); II-L-4, 250 – 275/67 – 73 (3.7 – 3.8); II-L-5, 280 – 300/63 – 67 (4.2 – 4.8); III-L-4, 250 – 270/67 – 73 (3.7); III-L-5, 290 – 310/58 – 60 (5.0 – 5.2); IV-L-4, 330 – 350/63 – 75 (4.7 – 5.3); IV-L-5, 340 – 370/58 – 63 (5.8 – 5.9). Mouthparts: Gnathosoma L 230; chelicera L 305, L/H 5.0, basal segment/claw L ratio 4.1; palp total L 438; L/H (ratio) P-1, 48/60 (0.8); P-2, 78/58 (1.4); P-3, 38/50 (0.8); P-4, 208/39 (5.4); P-5, 68/18 (3.9); L ratio P-2/P-4, 0.4, P-4/P-5, 2.3.

Derivatio nominis: lasios (Greek: λάσιος), villose, and derma (Greek: δέρμα), skin.

Remarks: Hydrodroma lasioderma differs from all other species of the genus in the very long, digitiform integument papillae. Like the two aforementioned species, it is a representative of an Hydrodroma with strong leg claws (L ≥ 45, ≥ 14 % of penultimate leg segments). It agrees with H. megalonyx in the relatively stout leg segments (L/H values of distal segments in general slightly above the maximum, but lower than minimum values in other species; absolute and relative claw length within the variability range of H. megalonyx ). Also with regard to many measurement values and proportions, H. lasioderma lies within the variability range of H. megalonyx , with the following exceptions: (1) Palp segment P-4 more slender (L/H> 4.7 vs. <4.3); (2) swimming setae numbers distinctly lower (total of all legs, 12 vs. 22 – 37).

Hydrodroma liberiensis Cook, 1966 from W Africa agrees perfectly with H. lasioderma regarding number and arrangement of swimming setae, but differs, in addition to the integument structure with very flat papillae, in gen- erally minor measurements of sclerites and appendages, more slender leg segments and distinctly lower acetabula numbers (<35 pairs) ( Cook 1966, Gerecke 2017).

Distribution: Only known from the type locality in Montagne d’Ambre at the northern end of Madagascar. It can be considered a Northern sister species of H. megalonyx from the S and W of the island.

Habitat: Probably a rhithrobiont, as suggested by the reduced number of swimming setae. The type locality is a low order stream with few pool areas; no standing waters exist in the surroundings.

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.