Hydrodroma kakadu sp. nov. (Figs. 14–17, 20; Tables 5–7) Type series: Holotype: male, dissected and slide mounted in Hoyer's fluid, Plunge Pool Gunlom Falls, Kakadu NP, Northern Territory, Australia, 30.ix.2005, 13° 25.17 S 132° 24.989 E (NTM). Paratypes: 9 males, 11 females same data as holotype (NTM, ZMAN, MNHP), four males and two females of these were dissected and slide mounted on Hoyer's fluid, same data as holotype. Further records: AUSTRALIA: NORTHERN TERITORY: Pond Jim Jim Creek near Jim Jim Campground, Kakadu NP, 23.vii.1994, 13°16 S 132°48 E, 3 males, 4 females; Pond in Jim Jim Creek at Jim Jim Crossing, Kakadu NP, 12°16 S 132°40 E, 22.vii.1994, 3 females; Mardugal Billabong, Kakadu NP, 12°16 S 132°40 E, 21.vii.1994, 12 males, 19 females, 2 deutonymphs; Plunge Pool, Gunlom Falls, Kakadu NP, 13° 25.917 S 132° 24.989 E, 25.vii.1994, 3 males, 1 female; Plunge Pool Edith Falls, Nitmiluk (= Katherine Gorge) NP, 14°19 S 132°34 E, 14° 10.899 S 182° 11.342 E, 30.vii.1994, 14 males, 26 females; same location, 02.x.2005, 17 males, 11 females; Pool Twin Falls, Kakadu NP, 12°16 S 132°40 E, 23.vii.1994, 3 maleS, 1 female; Lily Ponds Falls, Katherine Gorge NP, 14°19 S 132°34 E, 27.vii.1994, 1 female; Roper River, 06.x.2005, 14° 57.111 S 133° 13.401 E, 3 males, 6 females. NEW CALEDONIA: Oua Mendiou Rivière 30 km from mouth, 01.x.2000, 3 females; Dothio Rivière at crossing with road Thio­Nakety, 28.ix.2000, 4 females; Rivière de Pirogues at crossing with road Nouméa­ Yaté, 11.xi.2005, 22° 11.257 S 166° 43.397 E, 1 female; Hienghène Rivière, 19 km from mouth, 29.ix.2000, 2 males, 10 females, 1 deutonymph. Diagnosis: Characters of the genus Hydrodroma; the shape and setation of coxae, genital field and palps are similar to those found in H. pilosa; genital plates with 28–47 acetabula in 3–4 rows; swimming setae are absent on the anterior surface of IV­L­5. Description: Males (n = 5, Plunge Pool Gunlom Falls): Length of idiosoma 738–775, width 606–656. Total number of coxal setae varies between 13–17 (=15.4) on coxae 1, 12–16 (= 13.6) on coxae 2, 11–13 (=12) on coxae 3, 11–14 (= 12.4) on coxae 4. Further details of genital plate morphology are given in Table 5. Gnathosoma: capitulum length 153–172 (= 160); chelicerae total length 216–228 (= 222), claw 48–51 length (= 50). Palps without diagnostic features, for chaetotaxy of the palp see Figure 16 (measurements in Table 5). Number of swimming setae on legs are presented in Table 6. Female (n = 2, Plunge Pool Gunlom Falls): Length of idiosoma 688–1000, width 569–888. Number of coxal setae varies between 15–16 on coxae 1, 15–18 on coxae 2, 13–14 on coxae 3, 15 on coxae 4. Gnathosoma: capitulum L 172–185; chelicerae total length 241–245, claw 53–54 in length. Characters MALE FEMALE H. kakadu male (n = 9) female (n = 3) II­L­5 posterior 3–4 4–8 III­L­4 posterior 8–10 8–10 III­L­5 posterior 5–7 6–9 IV­L­4 anterior 7–8 8–9 IV­L­4 posterior 7–8 8–9 IV­L­5 anterior 0 0 IV­L­5 posterior 3–4 4–6 H. kakadu male (n = 2) female (n = 4) II­L­5 posterior 3–4 3–4 III­L­4 posterior 13–14 10–12 III­L­5 posterior 8–11 7–11 IV­L­4 anterior 11 10–11 IV­L­4 posterior 12–13 11–13 IV­L­5 anterior ­ ­ IV­L­5 posterior 6–7 6–7 Remarks: Hydrodroma kakadu sp. nov is most similar to H. kununurra sp. nov., and H. australis sp. nov. which both have more than one swimming setae on II­L­5. Hydrodroma kakadu can be easily distinguished from both species by the absence of swimming setae on the anterior side of IV­L­5. Furthermore, H. kakadu sp. nov., is distinguished by its relatively fewer acetabula, 28–47 (70–93 in 5–6 rows in H. kununurra sp. nov) and the ejaculatory complex is shorter, L 166–182 (188–209 in H. australis sp. nov., 216–236 in H. kununurra sp. nov). From H. americanus Marshall (in parentheses data taken from Wiles 1986) a species similar in the absence of swimming setae on the anterior side of IV­L­5, H. kakadu sp. nov. can be easily distinguished by its relatively fewer acetabula (69± 10 in both sexes) and males of H. americanus have twice as many setae present on the genital plate as females (mean number of genital plate seta: 94± 14 in males, 41± 6 in females). Due to the morphology of the genital field and the absence of swimming setae on the anterior side of IV­ L­5, specimens from New Caledonia show a general conformity with H. kakadu sp. nov. The New Caledonian specimens can be distinguished from the type­material of H. kakadu sp. nov. in its larger idiosoma and gnathosoma dimensions (e.g. idiosoma L males 831–1000, females 1100–1200; L genital plates 173–198 in male 192–203 in female; L capitulum in both sexes 219–244, L chelicera in both sexes 275–303; palp total L males 387–408, females 432–438) and in a higher number of swimming setae on III­IV­L (III­L­4p> 10, IV­ L­4a> 10, IV­L­5p> 6, see Table 7). Furthermore, the ejaculatory complex is longer, L 193–197. However, many of these characters are known to be variable and these specimens probably represent a New Caledonian race of H. kakadu sp. nov. The degree of variability of additional specimens is necessary before we can assess the taxonomic status of the New Caledonian specimens Etymology: The species is named after the Kakadu National Park. Distribution: Australia (Northern Teritory); New Caledonia. Habitat: Most specimens were taken from (plunge) pools in running waters. Like H. australis, the new species is obviously rheophilous.

Published as part of Pesic, Vladimir & Smit, Harry, 2007, Water mite species of the genus Hydrodroma Koch (Acari: Hydrachnidia, Hydrodromidae) from Australasia. Part I, pp. 31-44 in Zootaxa 1389 on pages 38-42, DOI: 10.5281/zenodo.175185