Hydrodroma perreptans (K. Viets, 1913 )

Gerecke, Reinhard, 2017, The water mites of the genus Hydrodroma (Acari, Hydrachnidia, Hydrodromidae) in Europe and Africa, Ecologica Montenegrina 13, pp. 1-24 : 9-11

Hydrodroma perreptans (K. Viets, 1913)

( Figs 4 A , C-E)

Type series: Holotype (sex not defined, palp measurements suggesting ♂) Cameroon, SMF 43924 , "Joh. Albrechts-Höhe, Bach b Mundame Kumba 24.9.1911 Damköhler leg. 1175", " Hydrodroma perreptans Viets. Type". State: Specimen widely lost, only one palp and one terminal leg segment left.

Material examined: SMF Zimbabwe, 51185 " Chimanimani Mountain Nt. Park. East South Rhodesia. Stream from Mt. Binga , Sign. SR.E. 19 C. Harrison leg. 13.5.1963 3896", 1 ♀ ; SMNH Kenia, 43334, " Mt. Elgon, Kaptega River ", 1 ♂ ; 43335, Kenia, " Nyeri, Chania River ", 1 ♀ ; FMNH Liberia, DC 87, no label, 1 ♀ .

Diagnosis (widely based on the female specimen from Liberia): Integument papillae heterogeneous: bluntly pointed larger papillae surrounded by six small, little prominent elevations ( Figs 4 D-E). Coxal setation: Cx-I medial setae not inserted on elevated projections, medial margin of Cx-I smooth; groups of 6-7 long distal tip setae at Cx-I and Cx-II, 8 densely arranged posterolateral setae at Cx-II and –III each. Coxal plate Cx-III+IV with blunt, medially directed anterior and posterior apodemes. Genital plates with 45-70 pairs of Ac, maximum number per transversal transect 5-6, and 25-30 pairs of medial setae. Legs with long claws (L> 40, ratio claw L/segment 5 about 20 %), segments relatively stout (e.g., L/H III-L-4, 4.1-4.7; III-L-5, 5.4-6.6; IV-L-4, 4.7-6.0; IV-L-5, 7.0-7.3); swimming setation extremely reduced (anterior/posterior): II-L-5 (0/0); III-L-4 (0/1-2); III-L-5 (0/1); IV-L-4 (0/1); IV-L-5 (0/1).

Description:

Both sexes: Colour undescribed. Lateral eyes with posterior lens distinctly smaller than anterior one ( Fig. 4 A ). Palp: Fig. 4 C; L ratio P-2/P-4, 0.4, P-4/P-5, 2.3-2.5. Total setae numbers Cx-I, 19; Cx-II, 25; Cx-III, 18; Cx-IV, 17.

Measurements: Male (SMNH 43334 [palp of type]): Idiosoma L/W 950/750; lateral eye anterior lens diameter 45, posterior lens L/W 45/20; L/W Cx-I+II, 240/170, Cx-III+IV, 270/245; genital plate L 210, Ac pairs n 70, genital setae pairs n 30; ejaculatory complex L/proximal chamber W 155/50; gnathosoma L 165; chelicera L 213, basal segment/claw ratio 3.4, L/H ratio 4.3; palp total L 358, L/H ratio (relative L %) P-1 0.84 (11) [lacking in type]; P-2, 1.39 (17) [1.25 (17)]; P-3, 1.19 (13) [1,07 (13)]; P-4, 4.46 (41) [4,45 (41)]; P-5, 3.57 (17) [4,00 (17)]. L/H (ratio in parentheses) I-L-4, 170/50 (3.4); I-L-5, 200/40 (5.0); II-L-4, 205/53 (3.9); II-L-5, 235/40 (5.9); III-L-4, 200/48 (4. 2); III-L-5, 230/40 (5.8); IV-L-4, 255/50 (5.1); IV-L-5, 265/40 (6.6).

Females (FMNH DC 87, SMF 51185, SMNH 43335): Idiosoma L/W 900-1100/750-900; lateral eye anterior lens diameter 52-55, posterior lens L/W 50/30; L/W Cx-I+II, 240-290/160-210, Cx-III+IV, 240-310/210- 290; genital plate 185-220/210-220, Ac pairs n 45-60, genital setae pairs n 25-28; egg diameter 100; gnathosoma L 175-185; chelicera L 225, basal segment/claw ratio 3.5-4.0, L/H ratio 5.0-5.6; palp total L 335-425, L/H ratio (relative L %) P-1, 0.81-1.00 (11-13); P-2, 1.25-1.39 (17-18); P-3, 0.91-1.12 (12-13); P-4, 3.89-4.50 (40-41); P-5, 3.33-4.40 (16-18). L/H (ratio in parentheses) I-L-4, 170-240/50-70 (3.4); I-L-5, 223- 300/45-55 (4.9-5.5); II-L-4, 210-325/50-68 (4.2-4.8); II-L-5, 250-358/30-55 (6.5-8.3); III-L-4, 185-305/45- 65 (4.1-4.7); III-L-5, 215-345/40-53 (5.4-6.6); IV-L-4, 215-390/45-65 (4.7-6.0); IV-L-5, 280-400/40-55 (7.0- 7.3).

Discussion: This species was described after a single specimen of uncertain sex which is now widely lost, and there is no other material authorized by K. Viets. Most of the few specimens available from museum collections derive from areas far distant from the type locality – in a geographical sense the closest specimen comes from Liberia (FMNH). Hydrodroma perreptans is extremely characteristic and cannot be confused with any species of the genus due to the widely reduced swimming setation. The specimens brought here together are surprisingly similar in important characters states and, as far as can be judged from the original description, in good agreement with the lost type specimen. Strong size differences between the small specimen from Liberia and the rather large one from Zimbabwe could result from intraspecific variability (observed to a similar degree in H. pilosa by Roy Wiles, pers. comm.), or indicate cryptic diversity.

Biology and distribution: As almost suggested by K. Viets (1914), the particular morphology of this species can be interpreted as an adaptation to life in running waters. The scattered records suggest a rather wide distribution in West, East and South Africa.

Figures

Figure 4. A. Hydrodroma perreptans, Liberia, female, lateral eye; B. H. ocellata, holotype male lateral eye; C-E. Hydrodroma perreptans, Liberia, female; C. Combined after original description and various slides, palp; D. integument in top view; E. integument in tangential view; F. H. ocellata, holotype male, integument in top view.