A new species of the genus Hydrodroma Koch, 1837 (Acari, Hydrachnidia, Hydrodromidae), with a key to the hitherto known six species of the genus in Australia Author Pesic, Vladimir Author Smit, Harry text ZooKeys 2011 143 13 22 http://dx.doi.org/10.3897/zookeys.143.2115 journal article http://dx.doi.org/10.3897/zookeys.143.2115 1313-2970-143-13 Hydrodroma meridionalis sp. n. Figs 1 A-G 2B3ATables 13 Type series. Holotype male, dissected and slide-mounted, Queensland, Lawn Hill Creek, cascades, Lawn Hill NP, 10.v.2005, 18° 41.806S , 138° 29.138E (QM). Paratypes: 12 males, 8 females, same data as holotype, one male and one female of them dissected and slide-mounted in Hoyer's fluid (QM); 35/33/0, Lawn Hill Creek at campground , Lawn Hill NP, 10.v.2005, 18° 42.011S , 138° 29.235E , four males and two females of them dissected and slide-mounted in Hoyer's fluid (RMNH). Further records. QUEENSLAND: Nankin Creek, Rockhampton, 04.v.1981, leg. A.P. Mackey, 2/3/0; ibid., 20.vii.1981, 2 [damaged]/2 [damaged]/0; ibid., 06.ii.1982, 1/1 [damaged] /0; Innot Hot Springs, 11.viii.1989, 1/0/0; Broken River near Conical Pool, Eungella NP, 18.ix.2000, 1/2/0; Crediton Creek, Eungella NP, 18.ix.2000, 2/7/0; The Millstream, upstream of Millstream Falls, Millstream NP, 16.ix.2000, 0/10/0; Wenlock River at crossing with road to Iron Range NP, 06.ix.2000, 1/1/0; Little Yabba Creek, S of Kenilworth, 20.ix.2000, 2/9/0; Cattle Creek at crossing with road to Finch Hatton Gorge, W of Mackay, 19.ix.2000, 0/6/1; Fletcher Creek, Dalrymple NP, 22.x.2005, 19° 49.125S , 146° 03.771E , 6/7/0; Alligator Creek, Bowling Green Bay NP, 22.x.2005, 19° 26.192S , 146° 56.862E , alt. 32 m a.s.l., 5/10/0 (0/1/0 mounted); Gregory River at Gregory Downs, 11.x.2005, 8° 38.811S ; 139° 15.008E , alt. 68 m a.s.l., 30/0; Waterview Creek at Jourama Falls, Paluma Range NP, 20.x.2005, 18° 51.729S , 146° 07.650E , 1/0/0; Davies Creek, Davies Creek NP, 13.x.2005, 17° 00.212S , 145° 34.180E , 1/2/0; Little Yabba creek at Charlie Moreland Campground, Kenilworth, 02.xi.2005, 26° 36.928S , 152° 39.105E , 11/15/0. NEW SOUTH WALES: School Creek near Morton NP, 05.xi.2001, 0/1/0; Upper Kangaroo River, N of Kangaroo Valley, 07.xi.2001, 1/1/0; Wattamolla Creek, Royal NP, 08.xi.2001, 0/2/0; tributary of Sawyers Creek, S of Kangaroo Valley, 06.xi.2001, 2/2/0; Bugong Creek near border of Morton NP, 05 .xi.2001, 6/9/1; Nymboida River at Platypus Flat, Nymboi-Binderay NP, 09.xi.2003, 30° 11.146S , 152° 41.499E , alt. 443 m a.s.l., 2/1/0; Urumbilum River, Bindarri NP, 7.xi.2003, 30° 15.966S , 152° 57.042E , alt. 137 m a.s.l., 3/2/0 (1/0/0 mounted); Mann River at Mann River Nature Reserve, 20.xi.2003, 29° 41.291S , 152° 05.815E , alt. 403 m a.s.l., 2/2/0 (1/0/0 mounted); Towamba River at Big Jack Rest Area, South East Forests NP, 11.xii.2003, 31° 53.885S , 149° 27.807E , alt. 271 m a.s.l, 1/6/0; Wog Wog River at crossing with Wog Way, 10.xii.2003, 37° 04.986S , 149° 29.027E , alt. 332 m a.s.l., 1/0/2; Bellinger River at Gordanville Crossing, 22.xi.2003, 30° 25.067S , 152° 50.845E , alt. 20 m a.s.l., 1/1/0; Minnemurra River at Minnemurra Rainforest, 18.xii.2003, 34° 38.183S , 150° 43.272E , 0/2/2; NORTHERN TERRITORY: Douglas River at Douglas Hot Springs, 01.viii.1994, 13°46S, 131°26E, 3/1/0 (1/1/0 mounted); Pond Chinaman Creek, 16 km S of Katherine, 29.vii.1994, 7/7/1; Pool near Jim Jim Falls, Kakadu NP, 23.vii.1994, 2/0/0; Katherine River near Visitors Centre, Katherine Gorge NP, 28.vii.1994, 4/1/0; 17 Mile Creek, tributary of Katherine River, Katherine Gorge NP, 28.vii.1994, 0/2/0. WESTERN AUSTRALIA: Pool Lennard River, Windjana Gorge NP, 09.ix.1998, 1/1/0; Plunge pool, The Grotto, S of Wyndham, 20.ix.1998 1/0/0; Pool Lennard Gorge, The Kimberley, 1.ix.1998, 2/1/0; Pool Valentine Springs, W of Kununurra, 18.ix.1998, 0/2/0; Plunge Pool Black Rock Falls, W of Kununurra, 18.ix.1998, 0/1/0; pools 3 km W of Lennard Gorge, The Kimberley, 10.ix.1998, 1/1/0; unnamed creek at crossing with Windjana Gorge road, 38 km N of Great Northern Highway, 30.ix.1998, 2/9/0; pool west of Tunnel Creek, Tunnel Creek NP, 30.ix.1998, 6 /6/0. VICTORIA: Crystal Brooke at Hospice Plain, Mt Buffalo NP, 10.x.1997, 0/1/0; Stony Creek downstream of Turret Falls, Grampians NP, 17.iii.2008, 37° 09.662S , 142° 29.789E , alt. 517 m a.s.l., 0/1/0; Mt Williams Creek, downstream of Kalymna Falls, Grampians NP, 18.iii.2008, 37° 19.034S , 142° 36.212E , 1/0/0; Rockpool Buandik Falls, 16.iii.2008, 37° 14.803S , 142° 16.914E , 1/2/0; Stringers Creek upstream of Walhalla, 09.iii.2008, 37° 56.006S , 146° 26.926E , alt. 360 m a.s.l., 0/1/0; Jump Creek, Mt Buffalo NP, 11.iii.2008, 36° 46.350S , 146° 47.636E , alt. 1468 m a.s.l., 1/1/0;. SOUTH AUSTRALIA: Onkaparinga River at Sundews Trail, Onkaparinga NP., 06.iv.2008, 35° 09.478S , 138° 34.791E , alt. 95 m a.s.l., 5/3/0. Diagnosis. Genital plate with 37-52 acetabula in 3-4 longitudinal rows; palp segments narrow (L/H ratio P-4 4.6-5.2, in both sexes); number of swimming setae: II-Leg-5 1; III-Leg-4p 7-9, III-Leg-5p 5-7, IV-Leg-4a 6-12, IV-Leg-4p 6-12, IV-Leg-5a 2-4, IV-Leg-5p 2-8. Description. Male. (holotype; in parentheses measurements of paratypes, if not given otherwise n = 5): Idiosoma L/W (800 -994/680- 813); integument papillae bluntly pointed. Coxal field: L Cx-I+II, 208 (206-226, x¯ = 215), Cx-III+IV, 244 (241-263, x¯ = 252), total number of coxal setae: 15-18 (18-22, x¯ = 20) on Cx-I, 18-19 (16-21, x¯ = 18) on Cx-II, 14 (11-16, x¯ = 14) on Cx-III, 17 (15-19, x¯ = 17) on Cx-IV. Genital plate (Fig. 1B, 3A): setae more numerous than in females, for measurements, Ac and setae numbers see Table 1; ejaculatory complex L 163 (163-177, n = 3, x¯ = 169). Capitulum vL 183 (188-203, x¯ = 195); chelicera (Fig. 1D) total L 247 (265-275, x¯ = 270), basal segment L 194 (209-216, x¯ = 213), claw L 51 (52-55, x¯ = 54). Palp as in female, for chaetotaxy see Fig. 2B, for measurements see Table 1. Number of swimming setae on legs are presented in Table 2. Female . (paratypes, n = 3): Idiosoma L/W 840 -1044/750- 938. Coxal field: L Cx-I+II, 219, Cx-III+IV, 247; number of coxal setae: 18-23 (x¯ = 21) on Cx-I, 14-23 (x¯ = 19) on Cx-II, 12-16 (x¯ = 14) on Cx-III, 14-19 (x¯ = 17) on Cx-IV. Shape of genital plate as in Fig. 1C, for measurements, Ac and setae numbers see Table 1. Capitulum vL 203-225 (x¯ = 217); chelicera total L 269-286 (x¯ = 278), basal segment L 214-235 (x¯ = 224), claw L 54-60 (x¯ = 56). Palp: For chaetotaxy see Fig. 1F, for measurements see Table 1. Numbers of swimming setae on legs are presented in Table 2. Figure 1. A-G Hydrodroma meridionalis sp.n. ( A-B , D, G = male holotype, C, E, F = female paratype) A = coxal and genital field B-C = genital field D = chelicera E = palp, lateral view F = palp, medial view G = ejaculatory complex. Scale Bars = 100 μm . FIgure 2. A Hydrodroma torrenticola (Walter, 1908), male (Croatia, Ombla spring): palp, medial view B Hydrodroma meridionalis sp. n., male holotype: palp, medial view. Scale bar = 100 μm . Figure 3. A Hydrodroma meridionalis sp. n., male paratype: genital field B Hydrodroma torrenticola (Walter, 1908), male (Serbia, Kozjak Mt., stream): genital field. Scale bar = 100 μm . Table 1. Morphometric data for the genital plate, palp and leg segments (2-6) for Hydrodroma meridionalis sp. n. Numbers (n) and length in µm (L) are given.

MALE		FEMALE
holotype	paratype (n =5, in parentheses x¯)	paratype (n =3)

Table 2. Number of swimming setae of Hydrodroma meridionalis sp. n., from Lawn Hill Creek (type series).

Hydrodroma meridionalis

Table 3. Number of swimming setae of Hydrodroma meridionalis sp. n. (Victoria: Stony Creek 1♀, Rockpool Buandik Falls 2♀, Jump Creek 1♂; Queensland: Gregory River 2♂, 2♀, Fletcher Creek 3♀, Cattle Creek 1♀, Waterview Creek 1♂, Davies Creek 1♂, 1♀, Alligator Creek 1♀, Broken River 2♀; New South Wales: Kangaroo Valley 1♂, 1♀, Bugong Creek 2♂, 1♀, Towamba River 1♀, Wog Wog River 1♂; Western Australia: Plunge pool, The Grotto, S of Wyndham, 1♂, Pool Lennard River 2♀,1♂, S of Kununnura 2♀, pool W of Tunnel Creek 2♂,1♀, unnamed creek at crossing with Windjana Gorge road 1♀; Northern Territory: Douglas River 1♂, 1♀, Chinaman Creek 2♂, 3♀).

Victoria		Queensland		New Southern Wales		Western Australia		Northern Territory
male (n =1)	female (n =3)	male (n =4)	female (n =10)	male (n =4)	female (n =3)	male (n =4)	female (n =7)	male (n = 3)	female (n = 4)

Remarks. Hydrodroma meridionalis sp. n. is most similar to the European Hydrodroma torrenticola (Walter, 1908), in the presence of one swimming seta on II-Leg-5, IV-Leg-5 anteriorly with 2-5 swimming setae and the presence of relatively large-sized leg claws. Hydrodroma torrenticola (in parentheses data combined from Wiles 1986 , Di Sabatino et al. 2010 and our material from Croatia and Serbia) differs from Hydrodroma meridionalis sp. n., in larger dimensions of the genital plates in the both sexes (L 225-275 µm ), a more slender genital plate in the male (compare Figs 3A with 3B), a longer ejaculatory complex (L> 200 µm ), stouter palp segments, especially P-4 (compare Figs 2A with Fig. 2B) and generally a lower number of swimming setae on III-Leg-4 (5-8 swimming setae). Variability. We found variability in the number of swimming setae (Table 3). The populations from Western Australia are characterized by generally lower number of swimming setae on anterior IV-Leg-5 (1-2 swimming setae, occasionally setae reduced on one side). Etymology. Named for its southern occurrence. Habitat. Most specimens were taken from pools of low order streams or from lotic areas of slow flowing streams. Like Hydrodroma torrenticola , the new species is obviously rheophilous. Distribution. Widespread in Australia (Queensland, Victoria, New Southern Wales, Western Australia, Northern Territory, South Australia).