Hydrachna Müller, 1776

Gerecke, Reinhard, 2004, The water mites of Madagascar (Acari, Hydrachnidia): a revised list completed by original material conserved at the Muséum national d’Histoire naturelle, Paris, Zoosystema 26 (3), pp. 393-418 : 395

Genus Hydrachna Müller, 1776

Hydrachna (Hydrachna) amplexa Koenike, 1898 ( Fig. 1 )

MATERIAL EXAMINED. — Madagascar. Centre, Lac Alaotra, 1946, J. Millot, 1 (B 15 A); west, Marais Marovoay près Majunga, no date, Waterlot, 1 (E 14 M).

DISTRIBUTION. — Madagascar.

DESCRIPTION

Male

Measurements: idiosoma L/W 2000/2000, coxal field L 850, frontal shield L/W 850/1300, eye capsule distance 440; genital field L/W 330/320, gonopore L/W 140/60; ejaculatory complex L 240, W of brachia proximalia 250; gnathosomal rostrum L 290, chelicera L 800, palp segments L/H P-1 130/200, P-2 150/110, P-3 185/65, P-4 85/40, P-5 35/17. Frontal shield ( Fig. 1A ) covering 1/3 of the dorsal surface, including the dorsocentral setae 1, but not the slit organs posterolaterad of the eye capsules, with equally rounded, but irregular posterior margin; coxae with extended borders of secondary sclerotization as typical for mature adults in the genus; genital field ( Fig. 1D ) posteriorly truncated, but with a convex margin of secondary sclerite, anteriorly with a weak indentation; about 12 paired hairs scattered between the medial acetabula, gonopore anteriorly elevated into a nose-like structure, flanked by a posteriorly-extending cover of fine hairs; gnathosoma with a straight rostrum ( Fig. 1C ), palp with only a few, fine setae as shown in Figure 1B .

Female

Obviously a recently hatched specimen with weak sclerotization and appendages misshapened by distortion; idiosoma L/W about 1500/1500, coxal field L 600, frontal shield 500/800, posteriorly indented, eye distance 320; genital field L/W 180/240; gnathosomal rostrum 280; palp segments L/H P-1 150/170, P-2 130/100, P-3 (200/65), P-4 (75/50), P-5 (40/20) (distal segments probably deformed due to weak sclerotization); genital field anteriorly convex (damaged in Fig. 1E ), with a few mediocaudal setae.

Discussion

This species was previously known from only one single deutonymph. The two adults bear an entire frontal shield while the frontal sclerotization of the deutonymph (as usual in this subgenus) comprises a pair of sclerites located medially from the lateral eye capsules. The female was found in the same area as the holotype (surrounding of Majunga, W coast, an arid area), while the male is from a far distant area with a different climate. For the time being, in view of the general agreement in measurements the two specimens should be considered as conspecific. However, for a definitive diagnosis of H. amplexa , collecting of adults of both sexes and developmental stages at the same site is desirable.

Hydrachna (Rhabdohydrachna) signata

Figures

FIG. 1. — Hydrachna amplexa Koenike, 1898; A-D, (MNHN B 15 A); A, frontal shield; B, palp; C, gnathosoma in lateral view; D, genital field; E, (MNHN E 14 M), genital field. Scale bars: 100 µm.