Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 15. 1992. (Budapest, 1992)

FRAGMENTA MINERALOGICA ET PALAEONTOLOGICA 15. BUDAPEST, 1992 p. 105-114 Parasite traces on a Bajocian gastropod by J. SZABÓ Abstract: Oriented, ramifying surface excavations were found on the shells of a Bajocian gastropod species, Proconulus baldensis (PARONA, 1894). The traces are indicative of a bryozoan species which collected food along the mantle edge of the host. INTRODUCTION From the Somhegy near Bakonybél (Bakony Mountains, Transdanubian Central Range, Hungary) a well preserved and rather rich Bajocian gastropod fauna was described recently (Szabó 1979, 1980, 1981, 1982, 1983, and Conti and Szabó 1987). More than 450 specimens, representing 54 species, were collected. The relatively high diversity suggests a wide scale of environmental adaptation of gastropods. However, the structure of benthic communities seems to be rather simple. That may be the reason why only a few cases of interspecific relations are documented in the available material. They consist mainly of repaired fractures, caused by predators and several shells with traces of epi- and endobionts. These phenomena are not common, only approximately 50 cases were observed con­cerning some 30 shells (a number of shell fractures are of doubtful origin and some shells bear more than one kind of traces). With the exception of five cases, these gastropods belong to two trochoidean species: Proconulus epuliformis SZABÓ, 1981 and Proconulus baldensis (PARONA, 1894) (Trochidae, Proconuli­nae). The most frequent trace fossil, a superficial lineation pattern occurs exclusi­vely on specimens of P baldensis. It has also been found on a specimen of the same gastropod species from Bivio Macerino (Umbria, Italy). Due to the overlap in terminologies of different fossil groups, it is necessary to mention that the terms in common refer consequently to gastropod shell mor­phology in description of orientation of the studied trace fossil. The figured specimens are deposited in the Geological and Palaeontological Department of the Hungarian Natural History Museum (inventory numbers: M.91.1, M.91.2) and in the Museum of the Hungarian Geological Institute (inven­tory number: J 10 144). DESCRIPTION The finds are shallow, nearly parallel-sided grooves of half-cylindric cross­section in the surface enamel of the shells (Plates I-IV). Their depth is nearly constant so the surface elevations (e.g. spiral ornament of the shell) are reflected in the undulations of the bottom (see Pl. II, Fig. 1). No decisive evidence has been found, not even in sections of the shell, whether the excavations are of subsurface

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