Hydrodroma pilosa Besseling, 1940

Gerecke, Reinhard, 2017, The water mites of the genus Hydrodroma (Acari, Hydrachnidia, Hydrodromidae) in Europe and Africa, Ecologica Montenegrina 13, pp. 1-24 : 15-18

Hydrodroma pilosa Besseling, 1940

( Figs 1 B-C, 6 A-E)

Type series: SMF, Neotype (here designated), The Netherlands, 43930 " Hydrodroma despiciens pilosa ♀, Bess., Cotype " "Voorst. Appensche Kolk, Juni 1940 Besseling coll. 5985" (slide mounted K. Viets); Paraneotypes: 43931, same data, but "5986" (slide mounted Viets). 43931a-b, same collecting site and date, from liquid collection K. Viets, slide mounted Gerecke, 1 ♂, 2 ♀♀.

Material examined: Coll. Gerecke, Tübingen: Germany, D 516, Mindelsee Südufer, 31.07.2005, 12 ♂♂, 1 ♀. Italy, I 351, Sardinia, Nurra (SS), Lago Baratz, Westufer , 60 m, U.Z.M. ML 34 04, 11.05.1986, 1 ♂, 1 ♀ . Coll. Moreno, Albaceite: Spain, ramblas salinas de Murcia , leg. Moreno, Rambla Moreras (vertido), UTM 30SXG461617, 14.06.1991, 1005 µS/cm, 1 ♀; Rambla Moreras (Majada), UTM 30SXG462631, 18.07.1991, 5600 µS/cm, 2 ♀♀; Rambla Rincones, UTM 30SXG512656, 18.07.1991, 3000 µS/cm, 1 ♂, 2 ♀♀; Rambla Majada, UTM 30SXG460635, 18.07.1991, 7600 µS/cm, 1 dn; Rambla Pantano, UTM 30SXG410732, 01.09.1992, 6200 µS/cm, 4 ♂♂, 8 ♀♀, 1 dn; Laguna Ojos de Villaverde , UTM 30SWH5495, 23.05.1998, 470 µS/cm, 1 ♀; Laguna Sanguijuela, UTM 30SWH4186, 31.10.1998, 700 µS/cm, 1 ♂; Laguna Salobreja, UTM 30TXK0487, 25.07.2007, 1330 µS/cm, 12 ♀♀; Laguna Cifuentes, UTM 30TWL3112, 26.07.2007, 321 µS/cm, 7 ♂♂, 2 ♀♀, 9 dn .

Specimens erroneously labelled as Hydrodroma despiciens (see there): NHMB Switzerland, 1340/1341, Wallis, leg. Gams, Charrat Okt. 1917, 1 ♂ on two slides [idiosoma/gnathosoma]; Algeria, 1342, Oued Kherma , 6.11.1923, Coll. Gauthier, XII/97, 1 ♂ ; 1343, Agoulmine , km 166 Azazga- Bougie, 13.9.1925, XIV/69, 1 ♂ ; 1345, Sahara, Imarera , 24.3.1928 coll. Seurat, XXV/95, 1 ♂ ; Turkey, 1346, Tatvan Bitlis, 24.7.1981 Coll. Özkan 1 ♀; SMF , Germany, 43884, Bremen, Waller Feld , 22.5.1906, Viets leg. 80, 1 ♂ ; 43886, Bremen, Kattenturm , 26.7.1906, Viets leg. 161, 1 ♀ ; Spain, 43872, Zaragoza, Raya , 16.4.1918, 3732, 1 ♀ ; 43873, Zaragoza, Condesa , 25.4.1919, 3753, 1 ♀ ; 43889, Zaragoza, Burago de Ebro , 26.6.1918, 3840, 1 ♀ ; 43892, Madrid, Granjilla , 27.5.1919, 3926, 1 ♀ ; Sweden, 51172, Angeranenland, River Ångerån, Drift , 28.- 29.4. 1978 K. Müller leg. 6804, 1 ♀. SMNH Denmark GULI 000046049, Själland , torvgrav v. Arresö, 23.05.1919, 1 ♂, 3 ♀♀ , undissected in Koenikes fluid.

Diagnosis (following Wiles 1985, completed after the material examined): Integument papillae of one type, distinctly separate, slender and sharply pointed, at transmitted light microscope no surrounding elevations visible. Coxal setation: Cx-I medial setae on strongly elevated projections ( Fig. 6 A ); groups of 4-5 long distal tip setae at Cx-I and Cx-II, 6-9 densely arranged posterolateral setae at Cx-II and –III each; total setae number of Cx-IV 22-30. Coxal plate Cx-III+IV with long posterior apodemes directed parallel to body axis. Genital plates with 38-87 pairs of Ac, maximum number per transversal transect 6-8 ( Fig. 6 B ). Legs with relatively short claws (L 28-36, ratio claw L/segment 5, 7-11 %). Leg segments relatively stout (e.g., L/H III-L-4, 4.1-4.6; III-L-5, 6.1-6.7; IV-L-4, 5.3-6.1; IV-L-5, 7.7-8.1; swimming setation rich (anterior/posterior): II-L-5 (0/8-10); III-L-4 (0/15-19); III-L-5 (0/10-16); IV-L-4 (14-18/15-20); IV-L-5 (5-9/11-16).

Description: Both sexes: Colour orange to red. L ratio P-2/P-4, 0.4; P-4/P-5, 2.3-2.4. Total setae numbers Cx-I, 18-23; Cx-II, 19-29; Cx-III, 21-27; Cx-IV, 21-30; swimming setae II-L-5, 6-10; III-L-4, 11-17; III-L-5, 10-15; IV-L-4, 25-34; IV-L-5, 14-21.

Measurements: Males [n=5, mouth parts 1]: Idiosoma L/W 1290-1900/1180-1700; L/W Cx-I+II, 274- 337/202-238, Cx-III+IV, 337-386/287-350; genital plate 296-323/130-144, Ac pairs n 76-95, genital setae pairs n 42-65; ejaculatory complex L 292 ( Fig. 6 C ); gnathosoma L/W 260-270/157-171; chelicera L 287, basal segment/claw ratio 4.6, L/H ratio 4.6; palp total L 493, L/H ratio (relative L %) P-1, 0.79 (12); P-2, 1.23 (17); P-3, 0.69 (10); P-4, 3.9 (43); P-5, 4.44 (18). L/H (ratio in parentheses) I-L-4, 198-213/61-72 (3.0- 3.3); I-L-5, 274-283/49-54 (5.2-5.6); II-L-4, 301-323/67-72 (4.3-4.6); II-L-5, 355-373/54-58 (6.2-6.7); III-L-4, 301-315/63-67 (4.5-4.8); III-L-5, 355-373/54-60 (6.1-6.7); IV-L-4, 359-404/63-70 (5.3-6.1); IV-L-5, 395- 413/50-54 (7.5-8.1).

Females [n = 3, palp 1]: Idiosoma L/W 1450-1900/1230-1740; L/W Cx-I+II, 332-337/229-247, Cx-III+IV, 386-427/337-382; genital plate 247-314/117-162, Ac pairs n 56-110, genital setae pairs n 30-35; egg diameter 157; gnathosoma L/W 256-278/170-180; chelicera L 355, basal segment/claw ratio 4.3-4.6, L/H ratio 4.7-4.9; palp total L 522, L/H ratio (relative L %) P-1, 0.78 (12); P-2, 1.08 (17); P-3, 0.63 (10); P-4, 3.33 (43); P-5, 4.20 (18). L/H (ratio in parentheses) I-L-4, 198-226/68-76 (2.6-3.3); I-L-5, 269-305/54-63 (4.3-5.5); II-L-4, 314-350/78-85 (3.7-4.3); II-L-5, 368-404/58-67 (5.9-6.7); III-L-4, 314-346/72-85 (4.1-4.6); III-L-5, 377-409/58-76 (4.9-6.7); IV-L-4, 404-454/72-85 (5.3-5.9); IV-L-5, 418-465/56-63 (6.6-7.8).

Discussion: Based on the original description, data presented by Wiles (1985) and Tuzovskij (2015), and a revision of material from various collections, H. pilosa differs from H. despiciens as follows: (1) Integument papillae of one type, distinctly away from each other, slender and sharply pointed; (2) II-L-5 with numerous (> 4) posterior swimming setae; IV-L-5 with swimming setae on both sides (anteriorly 5-9, posteriorly more than 10). In addition, H. pilosa differs from H. despiciens following Wiles (1985) in the serrulate setae at the distal margins of leg segments 4 and 5, which are higher in number and longer. A sexual dimorphism in numbers of medial genital setae reported by Meyer (1983) is supported also by data published by Tuzovskij (2015), but with a broader overlap.

The presence of numerous anterior swimming setae on IV-L-5 is also found in H. trigonometrica . This species (in parentheses) differs from H. pilosa in many features such as lower numbers of acetabula (25-30 pairs), relatively larger leg claws (L ratio claw/segment 5, 12-17 %), and minor dimensions of all parts of idiosoma and appendages. (e.g., genital plate L ♀ 155, ♂ 184). Pešić & Smit (2007a) gave a careful description of three species from Australia similar to H. pilosa in a high number of swimming setae. They found diagnostic differences in character states such as shape of genital plates, palp and leg segments, numbers of acetabula and genital setae, but also number and arrangement of swimming setae. An investigation on the formation of the integument papillae of the Australian species could give a hint on an eventual closer relationship between H. pilosa and the latter.

Locality records now available from bibliography and the revision of material from many collections suggest that H. pilosa is actually more frequent in Europe than H. despiciens and many ecological data published for the latter in reality refer to H. pilosa (see Di Sabatino et al. 2009). The pointed shape of papillae in Schmidt (1935, Figs 1-2 ) suggests that also that detailed anatomical treatment published under the name of H. despiciens , in reality deals with H. pilosa .

Biology and distribution: Detailed data on the life cycle of this species were published by Meyer (1985) and Smukalla & Meyer (1987) (both under the name H. despiciens ) and by Wiles (1987). Interestingly, larvae in German populations strongly preferred chaoborid hosts while populations of the British isles were also frequently found parasitizing chironomid midges. Parasitism on tipulid midges and Trichoptera was also observed. Meanwhile, the presence of this species is ascertained from nearly all parts of Europe. Concerning the tolerance of H. pilosa against electrolyte concentrations, the new records published here from nine sites in Southern Spain with a mean conductivity of nearly 3 mS/cm (for characteristics of these interesting sites see Moreno et al. 1995), support data from the Mediterranean ( Gerecke 1991) and Eastern Central Europe ( Kowalik 2002). In contrast, H. despiciens is more sensitive against water pollution and increased electrolyte contents and shows a preference for lower pH values ( Wiles 1985). Not surprisingly, the revision of collection material shows that records under the name of H. despiciens published from (semi)arid areas in Algeria by Walter (1925, 1928, 1931) obviously refer to H. pilosa (here recorded for the first time from Africa). Vice versa, no records document the presence of H. despiciens on the African continent.

Figures

Figure 1. Hydrodroma, general morphology. A. Hydrodroma pilosa, living specimen in oblique dorsal view; note the pale pigment dots of the separated, not encapsulated lateral eyes; B. H. pilosa, male in ventral view (legs detached); note dense coxal setation, paired genital plates with numerous acetabula and a circular anal pore sclerite. C. H. pilosa male, palp, medial view; note the extremely elongated dorsodistal extension of P-4. D. Hydrodroma sp. from Madagascar, at right papillose integument, at left underlying triangular net structure (A., D.: photograph Gerecke; B.-C. from Di Sabatino et al. 2010).

Figure 2. A-D: Hydrodroma despiciens, neotypes, Denmark. A. male, integument papillae near lateral eye in tangential view; B. male, integument in top view; C. male, anterior coxal plate with medial setal tubercles on Cx-I; D. female, genital field; E. female, integument in tangential view; F. male, chelicera.

Figure 6. Hydrodroma pilosa, Germany, Mindelsee. A. male, anterior coxal plate; B. male genital field; C. male, ejaculatory complex lateral; D. Integument in tangential view; E. integument in top view.