COMPARISON BETWEEN SOME EPIGEAN AND HYPOGEAN POPULATIONS OF ASELLUS-AQUATICUS (CRUSTACEA, ISOPODA, ASELLIDAE)

Epigean and hypogean populations of Asellus aquaticus (Linne) from Slo venia (A. a. aquaticus, A. a. carniolicus Sket, A. a. cavernicolus Rac ovitza) were compared morphologically with those from Romania (A. a. a quaticus, A. a. ssp. from Mangalia). The highly troglomorphic Slovenia n race (A. a. cavernicolus) was the reference for assessing the degree of troglomorphism in the Romanian cave population. Of 61 measured cha racters, most proved discriminative and many were classified according to their presumed nature (reductive and progressive troglomorphisms, paedomorphoses, K-strategy traits). In Slovenian hypogean population ( A. a. cavernicolus), a combination of regressive and progressive trogl omorphic traits is present: total depigmentation, eye and cuticular st ructural reduction, and body and appendage elongation. Some traits whi ch might indicate paedomorphosis also occur. The most significant shar ed characters of the assumed sister taxa A. a. cavernicolus (cave) and A. a. carniolicus (epigean) are isometric uropods and pereiopods, as well as the size of pleopod V and its large 'area'. Although some prog ressive troglomorphisms (appendage elongation) are not present in the Romanian hypogean population (A. a. ssp.-Mangalia), a number of adapti ve troglomorphic traits distinguish this population from the epigean o ne. It is totally depigmented, with reduced eyes and a smaller number of eggs. It also exhibits traits which might indicate paedomorphosis. Probable reasons for absence of the constructive troglomorphisms are d iscussed. The Romanian hypogean populations are not uniform. Specimens from Movile cave resemble some peltate asellids in head and pleotelso n shape. In the peripheral range of this hypogean population, however, there are signs of an introgression with the epigean population. Deta ils of the pleopods, as well as the biogeographical situation, support the conspecifity of A. a. ssp.-Mangalia with A. a. aquaticus.