Hydrodroma torrenticola ( Walter, 1908 )

Gerecke, Reinhard, 2017, The water mites of the genus Hydrodroma (Acari, Hydrachnidia, Hydrodromidae) in Europe and Africa, Ecologica Montenegrina 13, pp. 1-24 : 7-9

Hydrodroma torrenticola ( Walter, 1908)

( Figs 3 A-D)

Type series: Lectotype ♂, here designated, NHMB, on two slides: " Diplodontus torrenticolus ♂ Walter Neapel 10.9.1907 Coll. Steinmann " "1355 TYPUS leg. Steinmann [overpasted: Quelle bei Sarno, Neapel, 10.9.1907] V/24" [idiosoma]; same inscription, but "1356, V/25" [gnathosoma]; paralectotype ♂, same inscription, but "1354, V/13" [only idiosoma].

Material examined: NHMB, Switzerland, 1357 ♀ Walter , leg. Wacker Vierwaldstättersee b. Vitznau, 10- 7 m tief, 16.2.13; 1358-1359 Ennethorn, Vierwaldstättersee coll. Rohrer 1973, ♀, ♂ , on two slides; SMF, Germany, HEsta Heiligenrode, Klosterbach (DS), Staubereich, 52°58’55’’N 08°42’25’’E, 15 m, Gerecke & Wohltmann 15.08.2010, DFG-Projekt K.Viets, 6 ♂♂, 2 ♀♀ ; SMF 51136-37 , " H. despiciens ", OldenburgLand, Vehme , 20.07.1946, 226, 2 ♂♂ ; 51139, " H. despiciens ", Pegnitz bei Düsselbach, Pegnitztal, Nordbayern, H.-J. Stammer leg. 16.9.1949, 1035, 1 ♂; Spain, " H. despiciens ", 43891, 1 ♀ .

Diagnosis: Integument papillae of two types: Main papillae longish, apically rounded, shorter than in H. despiciens , upright or slightly curved in posterior direction ( Fig. 3 B ), each surrounded by six flat elevations in top view forming a hexagonal pattern ( Fig. 3 A, C ), in tangential view surrounding elevations pointed ( Fig. 3 A , lower part). Coxal setation: Cx-I medial setae not inserted on elevated projections (thus medial margin of Cx-I smooth, Fig. 3 D ); groups of 4-6 distal tip setae at Cx-I and Cx-II, a group of densely arranged posterolateral setae at Cx-II. Coxal plate Cx-III+IV with blunt posterior apodemes at 45° to median axis. Genital plates rather slender, with 45-70 pairs of Ac, maximum number per transversal transect 4-6, and 32-53 pairs of medial setae. Legs with relatively long claws (mean L in males 45-53, in females 33-60, ratio claw L/segment 5 L 11-18 %). Leg segments relatively stout (e.g., L/H I-L-4, 2.9-3.3; I-L-5, 4.5-4.8; II-L-4, 3.8-4.2; III-L-4, 3.9-4.2; III-L-5, 5.5-6.0; IV-L-4, 5.3-5.7; IV-L-5, 6.5-7.3; swimming setation (anterior/posterior): II-L-5 (0/1); III-L-4 (0/5-9); III-L-5 (0/4-7); IV-L-4 (7-10/7-11); IV-L-5 (3-4/4-8).

Description:

Both sexes: Colour orange to brown, rarely red. On each side, lateral eye lenses far distanced (> 100 µm), anterior lens rounded (diameter 50-70), posterior lens oval (length 60-70, width 40-55). Shape of mouthparts, coxae and excretory pore, and setation of palps as typical in all species of the genus, sexual differences very weakly developed. L ratio P-2/P-4, 0.38-0.44, P-4/P-5, 2.2-2.5. No sexual differences in total setae numbers: Cx-I, 20-30; Cx-II, 22-34; Cx-III, 14-23; Cx-IV, 14-26; swimming setae II-L-5, 1; III-L-4, 5-9; III-L-5, 4-7; IV-L-4, 15-20; IV-L-5, 7-11.

Measurements: Males: Idiosoma L/W 1340-1450/1000-1350; L/W Cx-I+II, 315-347/180-252, Cx-III+IV, 293-338/315-356; genital plate 239-266/90-153, Ac pairs n 45-58, genital setae pairs n 32-53; ejaculatory complex L/proximal chamber W 225-234/72-77, anterior arms W 225; gnathosoma L 225-248; chelicera L 302-342, basal segment/claw ratio 3.9-4.6, L/H ratio 5.6-6.3; palp total L 428-459, L/H ratio (relative L %) P-1, 0.89-1.08 (11-14); P-2, 1.21-1.48 (16-18); P-3, 0.80-1.00 (10-12); P-4, 4.21-4.47 (40-44); P-5, 3.89-4.50 (17-18). L/H (ratio in parentheses) I-L-4, 194-225/68-77 (2.8-3.3); I-L-5, 261-288/56-63 (4.5-4.7); II-L-4, 266-315/68-81 (3.7-4.5); II-L-5, 320-360/59-63 (5.5-5.9); III-L-4, 261-297/63-72 (3.9-4.1); III-L-5, 320- 347/54-63 (5.5-6.0); IV-L-4, 380-453/70-80 (5.3-5.5); IV-L-5, 405-450/60-68 (6.7-7.2).

Females: Idiosoma L/W 1460-1570/1340; L/W Cx-I+II, 369-383/266-279, Cx-III+IV, 374/369-383; genital plate 225-261/90-117, Ac pairs n 54-70, genital setae pairs n 25-40; egg diameter 115-180; gnathosoma L 292; chelicera L 387, basal segment/claw ratio 4.1, L/H ratio 5.4; palp total L 466-500, L/H ratio (relative L %) P-1, 0.83-0.93 (12-13); P-2, 1.25-1.29 (16-17); P-3, 0.85-1.00 (10-12); P-4, 4.13-4.57 (41-43); P-5, 4.00- 4.78 (17-19). L/H (ratio in parentheses) I-L-4, 175-239/58-81 (2.9-3.0); I-L-5, 240-315/50-68 (4.6-4.8); II-L-4, 240-342/58-86 (3.8-4.2); II-L-5, 300-405/50-72 (5.6-6.0); III-L-4, 230-333/55-81 (3.9-4.2); III-L-5, 285- 392/48-68 (5.7-6.0); IV-L-4, 315-505/55-90 (5.4-5.7); IV-L-5, 330-500/45-75 (6.5-7.3).

Discussion: The original description was based on several specimens ("einige Exemplare"), obviously of both sexes. Only the above mentioned two specimens are found in the slide collection of NHMB, but the existence of further tube material with syntypes cannot be excluded. The lectotype male 1355/56, most probably used for the species description, is designated here in order to give taxonomic stability for the species. Walter (1908) gave a very detailed discussion of the character states of this species in comparison with H. despiciens . In agreement with his interpretation, important diagnostic features are: (1) rounded, less extended integument papillae (the presence of two types of papillae is well visible in the paralectotype, the integument of the lectotype is poorly visible due to desiccation); (2) medial setae on Cx-I not inserted on projections; (3) leg segments stouter (as documented in many L/H ratio data listed above); (4) leg claws relatively stronger (as documented by the claw L/segment 5 L ratio data above). A further characteristic feature mentioned by Walter is the reduced number of swimming setae. However, if the variability of larger numbers of specimens is considered, swimming setae numbers may overlap. As first stated by Wiles (1985), the most important difference in this regard is not a reduction, but an increase: The anterior face of IV-L-5 bears 3-4 swimming setae in H. torrenticola , but it is completely lacking such setae in H. despiciens . If variability ranges in populations of both species are considered, several measurements in the original description retained important for recognizing H. torrenticolus become insignificant: The two species overlap in size of chelicera and palp segments as well as genital plates, and they agree also widely in the number of acetabula.

Biology and distribution: First described from a spring near Naples, H. torrenticola is obviously widely distributed in Mediterranean streams (e.g. Gerecke 1991). The morphological variability of populations from Central Europe (data above and Wiles 1985), the British Isles ( Wiles 1985) and Russia ( Tuzovskij 2015) show no remarkable deviations from the original description and other mediterranean material. The species is thus widely distributed in Europe, but does not extend to Fennoscandia.

Figures

Figure 3. Hydrodroma torrenticola, Germany, Heiligenrode. A-C. male, integument papillae; A, C, in top view, B in tangential view; D. male, anterior coxal plate.