THE STYGOBIONT GENUS BYTHIOSPEUM IN AUSTRIA - A BASIC REVISION AND ANATOMICAL DESCRIPTION OF B-CF-GEYERI FROM VIENNA (CAENOGASTROPODA, HYDROBIIDAE)

The type series of the eight Austrian nominal species of the stygobion t genus Bythiospeum, all originally described only from their shells, are compared morphometrically. Two series attributed to B. geyeri (Fuc hs, 1925) and one sample of an hitherto undescribed species from the t ype locality of B. tschapecki (Clessin, 1878), are also included in th is investigation. Several of the taxa have been classified as subspeci es or synonyms of other taxa in a variety of combinations. These class ifications were based on poorly defined, i.e. non-quantified, similari ties. It is demonstrated that, in the absence of anatomical data, syst ematic/taxonomic speculations exclusively based on conchological simil arities are pointless and misleading. In addition, Bythiospeum cf. gey eri from the groundwater of the river Danube in Vienna is described an atomically. It lacks eyes and epidermal pig ment, and is characterized by a number of presumably plesiomorphic (with respect to other hydrob iid genera) features, such as a simple penis, well developed hypobranc hial gland, and a duct connecting the prostate and mantle cavity.