Hydrodroma pacifica Pešić & Smit, 2021

Pešić, Vladimir, Smit, Harry & Mary, Nathalie J., 2021, Two new water mite species of the genus Hydrodroma Koch, 1837 from New Caledonia (Acari, Hydrachnidia: Hydrodromidae), Acarologia 61 (3), pp. 581-590 : 585-588

Hydrodroma pacifica Pešić & Smit sp. nov.

Zoobank: 7F836BF0-9B10-4686-B013-A469D331C630

Figs. 2 , 3 A-C, E-G

Material examined — Holotype ♂ ( MNHN), New Caledonia, Rivière Ouénaoué at crossing with Mt Koghi road, 22°10.856 S, 166°29.532 E, 13 Nov. 2005 leg. Smit, dissected and slide mounted . Paratypes: 1♀, same place and data as the holotype, leg. Smit, dissected and slide mounted, ( MNHN); 2♀, 1 deutonymph, La Coulée Rivière downstream of barrage, 22°10.404 S, 166°37.291 E, 16 Nov. 2005 leg. Smit, 1♀ dissected and slide mounted ( RMNH).

Other material — New Caledonia: Rivière Voh, 20°56 ′ 13.241 ″ S, 164°43 ′ 29.427 ″ E, 6 Nov. 2001 leg. Mary, 1♂ ; Unnamed Creek E of Pont Pérignon, Parc de la Rivière Bleue, 24 Sept. 2000 Smit, 1 ♀ (partly damaged); Coco amont, 5 Oct. 2000 leg. Mary; Rivière Confiance, leg. Mary, 1♂.

Diagnosis — Integument papillae rounded. Genital plates with 38–43 pairs of Ac in at most 3 longitudinal rows. Leg setae numbers: II-L-posterior 1 (short); III-L-4 posterior 4-6; III-L-5 posterior 3-6; IV-L-4 anterior 4, posterior 7; IV-L-5 anterior 0, posterior 3-4.

Description — General features —Integument with reticulation in deeper layers. Cx-I+II medially separated by a fine membranous line, with a row of long fine setae at medial margins of Cx-I, and posterior margins of Cx-II, -III, and -IV. Genital flaps with rounded lateral and strongly concave medial margins. Excretory pore sclerotized. Legs claws without claw blade, with a dorsal clawlet.

Males (holotype): Idiosoma L 910. Coxal field L 464; Cx-III W 456; L Cx-I+II 219, Cx-III+IV 256; coxal setae numbers: Cx-I, 22; Cx-II, 25; Cx-III, 19; Cx-IV 16. Genital plate slender, L 197, on each plate Ac number 38, with 23 setae, all hollow. Ejaculatory complex L 156.

Gnathosoma vL 194; chelicera total L 266, L basal segment 205, claw 63, L ratio basal segment/claw 3.3. Palp ( Figs. 3 C-D) total L 376, dL/H, dL/H ratio: P-1, 44/34, 1.27; P-2, 66/55, 1.2; P-3, 41/47, 0.87; P-4, 158/39, 4.0; P-5, 67/17, 3.9; L ratio P-2/P-4, 0.42. dL IV-L:

84, 141, 166, 250, 266, 244.

Female (paratype from Rivière Ouénaoué, n =1; in parentheses specimen from La Coulée Rivière, n =1): Idiosoma L 1050, W 1000. Coxal field L 484 (450); Cx-III W (516); L Cx-I+II 209 (216), Cx-III+IV 247 (256); coxal setae numbers: Cx-I, 19 (20); Cx-II, 23 (26); Cx-III, 24 (20); Cx-IV, 17 (15). Genital plate L 181 (183), on each plate Ac number 43 (44), with 21 (31) setae. Egg maximum diameter (n =2) 116-122.

Gnathosoma vL 197; chelicera total L 266 (256), L basal segment 198 (203), claw 65 (61),

L ratio basal segment/claw 3.1 (3.3). Palp ( Fig. 3F ) total L 375 (382), dL/H, dL/H ratio: P-1, 47/35, 1.35 (47/32, 1.47); P-2, 63/56, 1.12 (66/48, 1.37); P-3, 38/50, 0.75 (39/47, 0.83); P-4,

158/39, 4.0 (163/38, 4.27); P-5, 69/17, 4.1 (67/15, 4.5); L ratio P-2/P-4, 0.40 (0.41). dL IV-L:

86 (100), 147 (150), 166 (172), 256 (263), 275 (272), 238 (241).

Etymology — Named after the Pacific region.

Discussion — The new species resembles Hydrodroma cooki Pešić & Smit, 2007 , a species widely distributed in lentic waters in Australia ( Pešić & Smit, 2007b). It shares the presence of only one short swimming setae on II-L-5 and the absence of swimming setae from anterior IV-L-5. From the new species, H. cooki is distinguished by an increased number of genital acetabula (on each plate 63–161 Ac in 5–9 longitudinal rows) and swimming setae on III/IV-L (more than 10 on both posterior III-L-4 and anterior IV-L-4), legs with a relatively small-sized claw and by the shape of the integument papillae (pointed vs. rounded in H. pacifica sp. nov.). Hydrodroma wilesi Pešić & Smit, 2007 , reported from a helocrene spring and stream in the Northern Territory, Australia ( Pešić & Smit, 2007b), is similar in legs with a relatively large-sized claw and genital plate with <60 Ac in 4–5 rows. It differs from the new species in a reduced number of swimming setae on III/IV-L (III-L-4 posterior 1 – 2, III-L-5 posterior 1–3 rather short, IV-L-4 anterior 2–3, posterior 2–4, IV-L-5 posterior 1).

Distribution — New Caledonia.

Figures

Figure 2 Hydrodroma pacifica sp. nov. (A holotype ♂, Rivière Ouénaoué; B ♀, La Coulée Rivière): A – coxal and genital field; B – genital field. Scale bar = 100 μm.

Figure 3 A-C, E-G: Hydrodroma pacifica sp. nov. (A, C-E holotype ♂, Rivière Ouénaoué; F-G ♀, La Coulée Rivière): A – integument papillae; C – palp, lateral view; D, F – palp, medial view; E – IV-L-6; G – chelicera. B:H. cooki, ♀, Caranbirini Waterhole, Northern Territory: integument papillae. Scale bars = 100 μm.