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)

The greatest part of the valves of the large-statured oysters are densely pierced, the small borings indicate the activity of causticsponges which belong to the Family Clionidae. These borings are not only signs of liaerosion but of dwelling structures (domichnia), too. Openings limited to the surface of the valve indicate that the borings were mode in the shell of a living animal, reducing its solidity. Bored valves having pore openings on the inner surface or on both sides were empty. The larvae of the sponge settled onto the internal part of the shell after the oyster's death. The persence of these marine borers refers shallow-water enviroment (WARME, E. J. 1975). The author has, also studied another type of overgrowth (epoechia), on a shell of Babylonia eburnoides umbilicosiformis (T.Roth). I could observe a small worm-colony forming crust on the surface of the shell. The tubes of the worm-colony were filled and affixed to the snail-horn with limonite. The aperture of the shell was not covered by the worms. It seems possible that the colony was carried by the snail until its destruction. As a consequence of the displacement the worms, which otherwise led a sessile a way of life, they had more chance to obtain their food. Overgrowth produces synoechia among the associated two species. In the course of my investigations I have found shells with borings of cirriped larvae in many cases: Babylonia eburnoides umbilicosiformis (T.-Roth), Athleta rarispina (Lamarck), Turricula reguláris (Köninck), Egerea collectiva (Gábor), Hadriana egerensis (Gábor). On the surface of the shells openings of various numbers can be seen, but neither of them are perforated by the larvae. Cirripeds belonging to Genus Balanus compose solid skeleton and live attached in one place. In our case the cirriped is settled on the valve of an Ostrea cyathula (Lamarck). There is a small conefrustum type specimen on the Balanus. The presence of Ostrea indicates a rather strongly agitated water and a very slow and frequently interrupted sedimentation. Here the rock barnacle could find the suitable living conditions: nutriment, oxygen, protection from burying. After all, the decay of the two associated species might be caused by the fast coverage with limonitic sandy silt. It refers to the well preservation of the cirriped's test. The author could also observe Bryozoa remains on two Mollusc species. In the first case the thin Bryozoa-colony encrusted 36