Dr. Fűköh Levente szerk.: Malakológiai Tájékoztató 14. (Eger, 1995.)

DÁVID, Á.: Naticid prédation on Late-Oligocene (Egerian) corbulid bivalves collected from three localities of NE - Hungary

Naticid prédation on Late-Oligocene (Egerian) corbulid bivalves collected from three localities of NE - Hungary Dávid, Á. Key words: Naticid prédation, Corbulid bivalves, Late-Oligocene, Egerian, NE - Hungary. Abstract: Naticid prédation occurring on the shells of two Corbula species (Corbula basteroti Homes and Corbula gibba Olivi) collected from three localities of NE - Hungary is examined. Location of boreholes, distribution of complete, nonfunctional and unfinished borings on valves are studied in the case of both species. Different formations of the localities refer to differences in paleoenvironments. The boring activity of Naticids increase with the growth of grain size of the sediments. According to the avaiable data we can conclude that there is no significant connection between the presence of conchiolin sheets in corbulid valves and the evidence of anomalous naticid prédation on corbulids. Introduction At various outcrops in NE - Hungary Late Oligocène (Egerian) deposits can be studied. The clay-pit of Wind Brickyard at Eger (Fig. 1) is the type locality of the Egerian Stage. The sequence in the Eger area was described by Báldi (Báldi, T. 1983): - lower Rhyolte Tuff; - alternation of coarse sand, lagoonal variegated, carbonaceous lay and a thin gravelly intercalation; - alternation of shallow marine clayey silt and sandstone layers; - molluscan clay; - glauconitic, tuffaceous sandstone and sandy marl with a one metre thick intercalation of lithothamnian limestone and Lepidocyclina Marl. At Rozália cemetery, Eger (Fig. 1.) glauconitic, tuffaceous sandstone and molluscan clay is exposed. At Nyárjas Hill, Novaj (Fig. 1.) the first Egerian deposit overlies a Late Kiscellian deposit. It is glauconitic, tuffaceous sandstone as at Eger, including the lithothamnian limestone and Lepidocyclina Marl intercalations. These sediments are overlain by the Molluscan Clay. The succession ends with the Rhyolite Tuff (Báldi, T. et al. 1974). Corbula valves have been collected from different deposits of the above mentioned localities. These are as follows: - Wind Brickyard: molluscan clay, silty fine molluscan and ("x-layer"), limonitic, friable sandstone („k-layer"); - Rozália cemetery: molluscan clay; - Nyárjas Hill: molluscan clay. Naticid gastropods are infaunal predators that drill through the shells of their molluscan prey. Characteristic borehole signs the activity of the predator. According to the shape of the borehole we can speak about complete, nonfunctional and unfinished borings. With nonfunctional a situation is meant in which the shell is completely perforated, but in which the opening in the inner shell wall is still not large enough to insert the proboscis (Kitchell et al. 1981). Boring can be situated at the edge of a valve, too (Ansell, A. D. et al. 1983). The Corbula species are small infaunal bivalves burrowing shallow holes in the sediment than fix their valves by bissus. They are suspension-feeding organisms (Báldi, T. 1973).