Hydrodroma poseidon, Gerecke, 2020

Gerecke, Reinhard, 2020, The early derivative water mites (Acari: Hydrachnidia, superfamilies Eylaoidea, Hydrachnoidea and Hydryphantoidea) of Madagascar, Zootaxa 4727 (1), pp. 1-77 : 28-30

Hydrodroma poseidon sp. nov.

Figs 14 d – g , 15 e – h

Hydrodroma despiciens Gerecke 2004 partim

Hydrodroma capensis Lundblad 1946 , K.O. Viets 1964

Type series: Holotype ♀, MNHN Ac 1290, MD B 16 C Carion (road Antanarivo-Tamatave ), Angavakely , étangs, 1400 m, X.1946 Millot leg., slide mounted . Paratypes: same site and date, (3/4/0) slide mounted, Ac 1291 – 1295

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Material examined: SMF 51146, “Station forestière de Manjakatompo 80 km südl. Tananarive Madagaskar, Therezien leg. 30.12.1908, 3011” “ Hydrodroma despiciens ”, (0/1/0) .

Diagnosis: Integument with larger, rounded papillae each surrounded by a collar of smaller, irregular ones ( Figs 14 d , 15 f – h ). Medial margin of Cx-I with distinct projections associated with setal bases ( Figs 14 e , 15 e ). Genital field with very numerous Ac (100 – 180 pairs, maximum n per transect, 7 – 12); sexual dimorphism in genital plate setae number and density: ♂♂ 50 – 70 (ratio n/plate L 0.20 – 0.28), ♀♀ 35 – 50 (ratio 0.14 – 0.16). Leg segments slender (e.g., L/H ratio I-L-5, 4.5 – 6.1; II-L-5, 5.9 – 7.3; III-L-5, 5.0 – 7.0; IV-L-5, 6.5 – 8.4). Distal edges of I-IV-L-4-5 with thickened, bi- or trifurcated setae, particularly strongly developed and trident-shaped at III-L-5 ( Fig. 14 f ); ventral setae of IV-L-4-5 elongated; swimming setae (anterior/posterior) II-L-5, 0/1; III-L-4, 0/9-13; III-L-5, 0/6-9; IV-L- 4, 6-12/6-11; IV-L-5, 0[-1]/5-8; claw length (all legs) 23-30; L ratio claw/ I-IV-L-5, 6-13 [mean: 8] % (see Fig. 14 f-g).

Description: Colour unknown. Lateral eyes lens diameter anterior 35-50, posterior 30-45, separation 70-200. Tips of Cx-I with 4-5 strong setae. Groups of similar setae at anterior (about 5) and posterior edge of Cx-II (about 8) and Cx-III (6, resp. 2, slightly finer and shorter). Posterior margin of Cx-IV with 15-20 setae in a single, locally double row, posterolateral apodeme very long, subparallel to median axis or slightly oblique.

Measurements: Male: Idiosoma L/W 1125/1000; Cx-I+II, 270-290/170-180; Cx-III+IV, 280-310/300-310; genital plate 245-250/110-120, genital field with 120-140 pairs of acetabula (8-9 per transect) and 50-70 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 155-165/50-55 (3.0-3.1); I-L-5, 210-225/43-45 (4.9-5.2); II- L-4, 230-265/53-55 (4;3-4.8); II-L-5, 285-315/45-50 (6.3-6.6); III-L-4, 225-235/55 (4.1-4.3); III-L-5, 274-350/48- 50 (5.8-7.0); IV-L-4, 293-315/53-55 (5.3-6.0); IV-L-5, 315-350/45-48 (7.0-7.4). Mouthparts: Gnathosoma L 190- 200; chelicera no data; palp total L 433-438; L/H (ratio) P-1, 48-53/55-63 (0.8-0.9); P-2, 73-75/55-58 (1.3-1.4); P-3, 44-48/50 (0.9-1.0); P-4, 180-185/38-40 (4.6-4.9); P-5, 80-83/18 (2.2-2.3); L ratio P-2/P-4, 0.4, P-4/P-5, 2.2-2.3.

Female: Idiosoma L/W 1200-1500/ 1000-1375; Cx-I+II, 280-365/180-210; Cx-III+IV, 280-380/300-370; genital plate 230-330/110-160, genital field with 100-175 pairs of acetabula (7-12 per transect) and 35-50 pairs of medial setae. Distal leg segments, given as L/H (ratio): I-L-4, 170-213/55-65 (3.1-3.3); I-L-5, 225-320/48-53 (4.5-6.1); II-L-4, 255-320/58-73 (4.1-4.8); II-L-5, 295-375/48-55 (5.8-7.3); III-L-4, 245-295/63-70 (3.9-4.6); III-L-5, 250- 370/50-60 (5.0-6.8); IV-L-4, 295-405/55-70 (5.4-6.4); IV-L-5, 325-430/50-55 (6.5-8.4). Mouthparts: Gnathosoma L 210-260; chelicera L 298-368, L/H 4.6-4.9, basal segment/claw L ratio 3.6-4.3; palp total L 500-530; L/H (ratio) P-1, 53-65/65-70 (0.8-1.0); P-2, 83-93/60-65 (1.4); P-3, 53-55/55-60 (0.9-1.0); P-4, 210-223/43-45 (4.8-5.1); P-5, 90-95/19-20 (4.4-4.9); L ratio P-2/P-4, 0.4, P-4/P-5, 2.3-2.4.

Derivatio nominis: Poseidon (Greek: Ποσειδῶν), Greek god of the sea with a trident-shaped spear, like the leg setae of this Hydrodroma .

Remarks: In integument structure, shape and setation of coxae, leg proportions (rather slender segments and relatively short claws) and swimming setation (numerous, but only one posterior on II-L-5 and absent from anterior surface of IV-L-5), H. poseidon is very similar to H. despiciens from the northern hemisphere. The latter species differs in: (1) lower numbers of Ac (at maximum 70 pairs, 4-7 per transect); (2) absence of a sexual dimorphism in genital setation; (3) a stouter P-4 (L/H ratio <4.5) and (4) distal setae on leg segments more moderately developed, not trident-shaped.

Another three Madagascan Hydrodroma species are characterized by higher numbers of swimming setae (total n> 35). Among these, H. mesembrina , differs in a smooth medial margin of Cx-I, H. zhokhovi in an integument with simple papillae and the presence of 2 swimming setae on posterior surface of II-L-5; H. amoenoderma is easily distinguished by the presence of numerous anterior swimming setae on IV-L-5.

Both Lundblad (1946) and K.O. Viets (1964) reported the presence of H. capensis from Madagascar, considering quadrangular posteromedial apodemes of Cx-I+II as a diagnostic feature of that species ( Lundblad 1946: absence of such apodemes “as generally known the case also in our common H. despiciens ”). As demonstrated by Gerecke (2017), both authors tended to confuse H. despiciens with H. pilosa Besseling, 1940 , a species in fact having Cx-I+II with very simple or absent posteromedial apodemes. Instead, such apodemes are well developed in H. despiciens (see Gerecke 2017, Fig. 2 C ) and not suitable for separating H. capensis . Revision of slide material from SMNH and SMF show that populations recorded from Madagascar under the name of H. capensis do not have the doubled II-L-5 swimming seta characteristic of the latter. In view of high numbers of acetabula on the genital plates they are here attributed to H. poseidon .

A previously unpublished specimen from Manjakatompo (SMF 51146), identified by K.O. Viets (1964) as Hydrodroma despiciens , is also a representative of H. poseidon . From our present knowledge, H. despiciens is restricted to the W Palaearctic, all African records under this name refer to different species (Gerecke 2017).

Habitat: Standing waters.

Distribution: Madagascar, in addition to the type locality in the Central High Plateau, recorded from coastal areas in the west and southeast.

Figures

FIGURE 2. Family Eylaidae, genus Eylais (e.–f. from Koenike 1898, without sex and magnification information, modified). a.–b. E. degenerata male (MD 239); a. eye plate; b. palp, P-3–5; c.–d. E. voeltzkowi male (MD 235); c. frontal plate and integument with acetabula on the right side; d. gnathosoma with palp and chelicera; e. E. crenocula, eye plate; f. E. megalostoma, eye plate.

FIGURE 14. Family Hydrodromidae, genus Hydrodroma. a.–c. H. amoenoderma, female (MD 097); a. integument papillae; b. palp; c. coxal and genital field; d.–g. H. poseidon female (MNHN B 16 C); d. integument papillae; e. Cx-I+II; f. III-L-4–6 (detail. trident setae at higher magnification); g. IV-L-4–6.

FIGURE 15. Family Hydrodromidae, genus Hydrodroma. a.–d. H. amoenoderma, female (MD 151); a. Cx-I+II; b.–d. integument papillae in various views. e.–h. H. poseidon; e. Cx-I+II; f.–h. integument papillae in various views. i.–m. H. sp. inc. nr. lasioderma (MD 061); i. Cx-I+II; k.–m. integument papillae in various views.