Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 1994. Sectio Geographiae.(Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 21)
Dávid Árpád: Palaeo-occological and palaeo-pathological observations on upper oligocene molluscs (Eger, Hungary)
growing to one another (epoechia) (BOGSCH. L. 1968.). Because of the favourable conditions they were crowded in great masses and it affected frame deformation in a number of cases. The disfigurement of the oyster-shells might cause the animal's destruction in extreme circumstances. The author studied another type of symbiosis in the case an Athleta rarispina (Lamarck) specimen and alittle oyster-colony. One of the oysters has both valves. The mouth of the Athleta is not covered by the oysters' shell. So, presumably, the oysters were carried by the snail. The Athleta was a large-figured, thick-shelled gastropod, which followed predatory way of life. It might have been not too difficult for it to carry the oysters. And the oysters, however could participate in the residues of the gastropod's nutriment. This type of symbiosis is called commensalism. The author have found oyster-shells on an Egerea collectiva (Gábor) specimen, too. Its aperture was covered by the oystercolony. This proves that the Egerea had become extinct before the oysters settled on it. The symbiosis of the Ostrea sp. is not limited to one, or two species only. I could observe similar occurrences in case of other gastropods, too. These are the following: Turricula reguláris ( Köninck , Polinices josephinia olla (De Serres), Turritella beyrichi percarinata (Telegdi-Roth), Galeodes basilica (Bellardi), Globularia gibberosa callosa (Noszky) The oysters live attached in one place on the solid sea-bottom (cementation). In the present case, mainly shells of died gastropods served as a bottom for its larvae. The mostly broken, deficient and rolled shells indicate that the decay of the snails didn't take place locally. The streaming water caused them to get to the place where the oyster larvae settled on them. It explains how the shell of the Turritella, which otherwise lives within the bottom sediments could get among the tests of the other gastropods. Owing to the flowing water the sedimentation was paused, or was not significant. It was favourable for the sessile habitude oysters. Conclusion can be drawn from the form of the bivalves for the changes or peridicity of the current. The rounded forms are characteristic of such simple organisms that live in a relatively undisturbed envrionment. 35
