Int. J. Speleol. II (1981), pp. 91-103. Distribution of Ostracods in the Groundwater of the North Western Coast of Euboea (Greece) Dan L. Danielopol* SUMMARY Freshwater fauna from 20 wells located 15-200 m from the seashore as well as marine interstitial fauna from the coastal zone around the village Aghios Georghios (Cape Likhada) have been in- vestigated. Freshwater hypogean ostracods live mainly in protected wells having clean bottom and little particulate organic matter from which the water is moderately pumped. Epigean fre- shwater ostracods dominate in unprotected wells with large amounts of organic matter on the bottom. There is a sharp difference between the ostracod fauna living in fresh groundwater (mainly Cypridids) and those living in coastal marine interstitial habitats (marine Cytherids and Polycopids). It is suggested that in the Mediterranean realm the hypogean fauna could be found easily in protected wells with little organic matter accumulation, where water is moderately pumped. INTRODUCTION The scarce information on freshwater interstitial fauna of Greece has recently been reviewed by Bou (1975) and Matsakis (1975). Bou visited Greece during 1969 and 1971 and extensively sampled hypogean fauna (see his report, 1975), Prior to 1969, Schafer (1945) and Stephanides (1948) sampled fauna from wells, the former collected in Thessaly around Carla Lake at about 25- 40 km in from the sea coast; the latter investigated several wells in Corfu Island. Schafer found a rich hypogean ostracod fauna and also reported (1951) that some of the well fauna from Thessaly came from a limestone area. Therefore it was not clear if Schaffer's ostracods live in a porous aqui- fer or in a karstic one. Considering the typical interstitial fauna accompaning the ostracods from Thessaly (Microcharon (lsopoda), Parastenocaris, Sigma- tidiwn (Harpacticoida) as well as the minute size of ostracods belonging to the genera Kliel/a, Nannokliel/a and Mixtacandona (see Schafer, 1945), I hy- pothesized (1971 and 1977) that the ostracods should be interstitial inhabi- tants. Stephanides (1948), quite opposed to Schafer, found only epigean fau- na in the wells of Corfu. Bou offered me the ostracods he collected in many wells in Greece, and I found that, in addition to the well samples containing blind hypogean ostra- cods, there were also some samples in which epigean fauna dominated. In or- • Limnologisches 1nstitut, Berggasse 18, A-1090 Wien.