Notes on the Hyadesia species (Acari, Astigmata, Hyadesidae) of the Oudemans collection, with a redescription of Hyadesia Vietsi Womersley, 1961

INTRODUCTION The mites of the genus Hyadesia are of cosmopolitan distribution. They live in the intertidal area where they feed mainly on algae in salt water. Up to now 16 species have been described in this genus. Most of these species have been inadequately described and it is generally very difficult to recognize them from the original description and figures. Through the courtesy of Dr. L. van der Hammen of the Leiden Museum, we were able to examine the hyadesid mites conserved in that Museum. The present paper is devoted to the study of this collection. It allows us to redescribe Hyadesia vietsi Womersley, 1961, and to record some new localities for Hyadesia fusca (Lohmann, 1894). Hyadesia vietsi Womersley, 1961 (figs. 1-7) This species is known after two female specimens. The holotype is in the Rijksmuseum van Natuurlijke Historie at Leiden, the paratype in the South Australian Museum. Redescription of the female holotype (figs. 1-7). — Length of idiosoma 560 μ, maximum width 375 μ. Dorsum: Propodosomal shield wider than long. The cuticle behind this shield is soft. There is a small depression behind the sc i and sc e setae, representing a vestigial sejugal furrow. Oil glands very large. From the orifice of the oil-gland arise, at each side, two narrow and shallow furrows, one directed anteriad, the other posteriad. These two furrows present several branches, some of them ending into oval symmetrical orifices. A similar structure of oil furrows has already been described in other species of Hyadesia (Fain, 1975). Venter: Genital suckers not observed. Anus termino-ventral.