Hydrodroma argentinensis Pešić & Smit, 2022

Pešić, Vladimir & Smit, Harry, 2022, Water mites of the genusHydrodroma Koch, 1837 (Acari, Hydrachnidia: Hydrodromidae) from Argentina, with description of two new species, Acarologia 1837 (1), pp. 68-83 : 72-78

Hydrodroma argentinensis Pešić & Smit sp. nov.

Zoobank: 87C5C9D7-5081-4A02-87FE-0774D298DBA1

Figures 4-6

Material examined — Holotype ♂ ( MBR), Argentina, Prov. Río Negro, Manso River , Nahuel Huapi NP, 41º20.858 S, 71º36.300 W, alt. 817 m, 17 Feb. 2018, leg. Smit, dissected and slide mounted . Paratypes: 2♂, 2♀, same data as holotype, 1♀ dissected and slide mounted ( RMNH); Argentina, Prov. Río Negro, Rio Manso Medio near Cascada Los Alerces, Nahuel Huapi NP, 16 Nov. 1999, leg. Smit, 1♂, 6♀ ( MBR).

Other material — Argentina: Prov. Neuquén, Río Collón Curá, 30 km E of Junín de los Andes, 39°59.8333 S, 70°50.1075 W, 12 Nov. 1999, leg. Smit, 1♀ ( RMNH); Prov. Neuquén,

small lake ± 15 km N of Villa La Angostura, along Rutá 234, Lanín NP, 12 Nov. 1999, leg.

Smit, 3♂, 12♀ (1♂, 1♀ dissected and slide mounted, RMNH).

Diagnosis — Integument papillae of two types: main papillae longish, each papilla surrounded by six very flat elevations forming a hexagonal pattern, in tangential view apically rounded ( Figures 4 C-D, 6C-D). Posteromedial projections of Cx-I short. Genital plates with 58–81 pairs of Ac in at most 5 longitudinal rows. Legs with moderately long claws (L 31-34 µm; L ratio claw/segment 5, 10-15%). Leg setae numbers: II-L-posterior 0; III-L-4 posterior

km N of Villa La Angostura; B, D – ♀, small lake ± 15 km N of Villa La Angostura): A-B – integument papillae, in top view; C-D – integument papillae, in tangential view; E – ejaculatory complex, posterior view; D – ejaculatory complex, anterior view.

7-10; III-L-5 posterior 6-8; IV-L-4 anterior 7-10, posterior 6-9; IV-L-5 anterior 0-3, posterior

5-7.

Description — Posteromedial projections of Cx-I short, separated by a fine membranous line. Genital flaps with rounded lateral and strongly concave medial margins, each with 63 (holotype, paratypes and other specimens: 58-81) Ac, and 31 (25-38) setae, with sexual dimorphism (♂: hollow, ♀: more solid and flat). P-2 with three pectinate mediodistal setae, similar in size.

Male (holotype ; in parentheses some measurements of paratypes, n = 2; in square brackets some measurements of the specimen from small lake ± 15 km N of Villa La Angostura): Idiosoma L 894 (950) [1190], W 825. Coxal field L 463 (420) [531]; Cx-III W 509 (472) [652];

L Cx-I+II 222 (231) [266], Cx-III+IV 241 (234) [261]. Coxal setae numbers: Cx-I, 14 (11-13)

[14]; Cx-II, 21 (18-20) [26]; Cx-III, 21 (16-21) [22]; Cx-IV 15-17 (14-17) [18]. Genital plate

L 214-216 (216-219) [220-223]. Ejaculatory complex L [205].

Gnathosoma vL 180 [188]; chelicera total L 236 [261], L basal segment 195 [217], claw 46 [52], L ratio basal segment/claw 4.3 [4.2]. Palp total L 382 [407], dL/H, dL/H ratio: P-1, 48/34,

1.4 [45/36, 1.26]; P-2, 64/52, 1.24 [72/54, 1.33]; P-3, 39/52, 0.76 [41/56, 0.72]; P-4, 158/36,

4.4 [169/38, 4.5]; P-5, 73/19, 3.9 [80/19, 4.3]; L ratio P-2/P-4, 0.41 [0.43].

dL I-L-1-6: 50 [63], 78 [81], 100 [100], 161 [173], 219 [236], 225 [234]; claw L 33 [33] –

14.8 (13.4) [13.9] % L I-L-5. dL II-L-1-6: 55, 94, 125, 222, 272, 272; claw L 34, – 12.5 (11.1)

% L I-L-5. dL III-L-1-6: 53, 106, 127, 211, 250, 254; claw L 33, 13.1 (11.1) % L I-L-5. dL IV-L-1-6: 100, 141, 177, 261, 284, 279; claw L 31, – 11 (10.2) % L I-L-5.

Female (paratype from Manso River, n = 1; in square brackets some measurements of the specimen from small lake ± 15 km N of Villa La Angostura): Idiosoma L 1016 [1000], W 818. Coxal field L 484 [477]; Cx-III W 603 [575]; L Cx-I+II, 234 [230], Cx-III+IV, 255 [242].

Coxal setae numbers: Cx-I, 16 [15]; Cx-II, 23 [22]; Cx-III, 20 [16]; Cx-IV, 16 [16]. Genital flaps large, L 183-189 [184].

Gnathosoma vL 191 [203]; chelicera total L 274 [261], L basal segment 213 [211], claw 59

[52], L ratio basal segment/claw 3.6 [4.1]. Palp total L 423 [422], dL/H, dL/H ratio: P-1, 48/41, 1.2 [45/38, 1.2]; P-2, 70/55, 1.27 [70/50, 1.39]; P-3, 42/52, 0.82 [43/52, 0.84]; P-4, 180/39, 4.6

[180/36, 5.0]; P-5, 83/17, 4.8 [84/19, 4.5]; L ratio P-2/P-4, 0.39 [0.39].

dL I-L-1-6: 58 [59], 84 [81], 106 [97], 183 [172], 241 [234], 238 [229]; claw L 33 [34], –

13.5 [14.5] % L I-L-5. dL II-L-1-6: 56, 105, 136, 245, 294, 284; claw L 33, – 11.1 % L I-L-5.

dL III-L-1-6: 64, 108, 135, 222, 278, 272; claw L 32, – 11.5 % L I-L-5. dL IV-L-1-6: 98, 150,

194, 287, 325, 299; claw L 34, – 10.5 % L I-L-5.

Etymology — Named after the country where the new species was collected.

Discussion — In regard to the shape of the coxal field with relatively short, medially directed posteromedial projections of Cx-I, the new species resembles H. despiciens , a species considered previously to have a nearly cosmopolitan distribution (see Gerecke 2017 for a discussion). In former times, Hydrodroma populations from Brazil ( Lundblad 1941), Argentina ( Cook 1980) and Chile ( Cook 1988) have been attributed to H. despiciens s. str., while six additional subspecies of the latter were introduced for other South American populations (see below). Recently, H. despiciens was redescribed by Gerecke (2017) allowing a reliable identification and enhancing the taxonomic status of populations previously assigned to that species. Studies on extra-European populations, e.g., from Australia ( Pešić and Smit 2007a,

b, 2011) have already shown that the concept of a cosmopolitan distribution of H. despiciens must be rejected.

In addition to the relatively smaller claw (mean L in males 27-29, in females 29-30 µm; L ratio claw/segment 5, 8-12%; data taken from Gerecke 2017), H. despiciens , can be separated from the new species from Argentina by the presence of one swimming seta on II-L-5 and an increased number of swimming setae on III/IV-L (more than 10 on both posterior III-L-4 and anterior IV-L-4). Moreover, H. despiciens differs in the absence of swimming setae from anterior IV-L-5. However, swimming setae numbers of single segments may overlap and the numbers of all segments must be considered together.

Based on the original descriptions, we give here a brief overview of the South American subspecies of H. despiciens with their main features (if not mentioned otherwise, data taken from original descriptions or calculated from figures given therein). Cook (1988) stated that it is more likely that some of these subspecies deserve to be ranked as distinct species.

Hydrodroma despiciens brevirostris Lundblad, 1941 , was described from a pond near S. Antonia in Villarica, Paraguay. Based on the original description, the female holotype (prep. 23331, NHRS) is characterized by the presence of swimming setae on II-L. Two other females (preps. 2330 and 2332, both NHRS) included by Lundblad (1941) in the type series, however, probably are not conspecific with the holotype. Both paratypes, as mentioned by Lundblad (1941) do not possess swimming setae on II-L and dorsodistal seta on the medial surface P-2 is longer and slender (hair-like) as in H. longiseta (see above for a description). K. Viets (1954a) already suggested that these females should be assigned more correctly H. to longiseta .

Hydrodroma despiciens pauciseta Lundblad, 1944 was described from a stream in Sanibeni ( Peru) on the basis of a single female. The characteristic feature mentioned by Lundblad (1944) for this subspecies is the reduced number of swimming setae (III-L-4, 1; III-L-5, 2; IV-L-4, 1-2; IV-L-5, 1).

Hydrodroma despiciens clavipes Lundblad, 1953 was described from Colombia, and later on considered by Cook (1980) a separate species on the basis of material collected from Mexico.

In regard to the absence of swimming setae on II-L and a strongly reduced swimming setation on III/IV-L (one single, short seta each III-L-4/5, and IV-L-4/5) this species seems to be closely related to H. despiciens pauciseta Lundblad, 1944 .

Hydrodroma despiciens macronyx K. Viets, 1954 was described from the river Beberibe in the Brazilian state Pernambuco. In addition to the absence of swimming setae on II-L and reduced swimming setae numbers on III/IV-L (III-L-4 with 3-5 swimming setae; IV-L-4 with 3 in ♂, 6-7 in ♀ ; IV-L-5 with one in ♂, 3 swimming setae in ♀) this subspecies is characterized by large leg claws (42 µm), shortened swimming setae on III/IV-L and slender palpal segments, especially P-4 (L/H ratio P-4 6.3).

Hydrodroma despiciens crassiseta K. Viets, 1954 , was described from the Brazilian Amazon region (Igarapé do Guaranazal). Based on the original description, this subspecies differs from other subspecies of H. despiciens by an increased number of swimming setae on II-L (II-L-4 with 4; II-L-5 with 10 swimming setae). Hydrodroma despiciens micronyx K. Viets, 1954 , was described from a swamp in Recife, northeastern Brazil. It resembles H. despiciens crassiseta from which it differs in reduced numbers of swimming setae on II-L (II-L-4 with one, II-L-5 with two swimming setae).

Variability — We found considerable variation in the number of swimming setae on the anterior IV-L-5 between populations from rivers and lakes (a small lake in Lanín NP). Most specimens (eight out of 15) from the small lake N of Villa La Angostura did not have swimming setae on anterior IV-L-5, while other specimens bear here at least one (rarely two) swimming seta(e) at least on one leg; three specimens possessed swimming setae on anterior IV-L-5 on both legs. In the population from the Manso River most specimens possessed 1-2 swimming setae on the anterior IV-L-5 but several specimens were without swimming setae on anterior IV-L-5 on one or both legs.

Distribution — Argentina.