Hydrodroma peregrina ( Koenike, 1905 )

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 : 69-71

Hydrodroma peregrina ( Koenike, 1905)

Figures 1-2

Material examined — Argentina, Prov. Río Negro, Río Negro near General Conesa, 9

Nov. 1999, leg. Smit, 1♀ dissected and slide mounted ( RMNH).

Morphology — Female — Integument papillae apically rounded ( Figure 1C). Cx-I+II with well-developed, medially directed projections of Cx-I separated by a fine membranous line as indicated in Figures 1A, 2B. Genital flaps each with 75 Ac in at most 6 longitudinal rows and 33 setae, all solid and flat ( Figure 1B). Legs with relatively small claws (L 22-30; L ratio claw/segment 5, 6-11 %). Leg setae numbers: II-L-5 posterior 7; III-L-4 posterior 11; III-L-5 posterior 9; IV-L-4 anterior 11, posterior 12; IV-L-5 anterior 0, posterior 8-9. P-2 with three pectinate distal setae on the medial surface, dorsodistal seta long and slender ( Figure 1C). Measurements: Idiosoma L 1269, W 1080. Coxal field L 541; Cx-III W 559; L Cx-I+II,

288, Cx-III+IV, 311. Coxal setae numbers: Cx-I, 12; Cx-II, 20; Cx-III, 17-19; Cx-IV, 14-15.

Genital field W 247, genital plate L 209, maximum W 109.

Gnathosoma vL 223; chelicera total L 303, L basal segment 244, claw 63, L ratio basal segment/claw 3.9. Palp total L 500, dL/H, dL/H ratio: P-1, 55/50, 1.1; P-2, 86/65, 1.33; P-3,

59/59, 1.0; P-4, 208/48, 4.3; P-5, 92/23, 3.9; L ratio P-2/P-4, 0.41. dL I-L-1-6: 72, 105, 128,

211, 250, 236; claw L 27, – 10.6 % L I-L-5. dL II-L-2-6: 125, 156, 272, 319, 269; claw L 22, –

6.9 % L I-L-5. dL III-L-2-6: 128, 159, 268, 306, 288; claw L 30, – 9.8 % L I-L-5. dL IV-L-1-6:

136, 184, 253, 372, 378, 317; claw L 30, – 7.9 % L I-L-5.

Remarks — Hydrodroma peregrina is often reported from the Neotropics, from Argentina to Mexico ( Lundblad 1941 ; Cook 1980). It was originally described by Koenike (1905) from the Rio Grande do Sul in Brazil. In the original description, Koenike (1905) illustrated the coxal field but did not give neither an illustration of palp nor information on the leg setation.

In describing specimens from Paraguay and Brazil, Lundblad (1941) stated that he did not find any differences with Koenike’s type material. We were able to locate the type material of H. peregrina in the Koenike’s collection in the Museum für Naturkunde der Humboldt-Universität Berlin. The type material was in very poor condition but it was possible to recognize the presence of the characteristic long, medially directed posteromedial projections of Cx-I. In regard to the shape of coxal field and palps our specimen agrees well with specimens H of. peregrina s. str. as illustrated by Lundblad (1941).

In describing specimens from Mexico, Cook (1980) mentioned that his specimens differ from each other in proportional size of the genital field, separating the large and the small genital field forms, respectively. Our specimen as well as the specimen from Brazil illustrated by Lundblad (1941) have genital field proportions more or less intermediate between those of the two Mexican forms (see Cook 1980).

Hydrodroma peregrina robusta K. Viets, 1954 , a subspecies described by K. Viets (1954a) from northeastern Brazil differs from the nominal species in the absence of swimming setae on II-leg and the characteristic slender shape and setation of the palp (P-4 L/H ratio 6.0); P-2 with four long and slender, a hair-like mediodistal pectinate setae, see Figures 16a-b in K. Viets 1954a). In regard to these differences, there is no reason to support the assignment of this taxon as subspecies of H. peregrina and we propose to the taxon to the level of a separate species H. robusta stat. nov.

Distribution — Brazil, Paraguay ( Koenike 1905 ; Lundblad 1941), Mexico ( Cook 1980), Argentina (this paper). It is possible that populations formerly attributed to H. peregrina represent several distinct species.