This strange structure is clearly not a gastropod and is probably not even a Miocene fossil.
Harzhauser, M.; Neubauer, T.A.; Georgopoulou, E.; Harl, J. (2014). The Early Miocene (Burdigalian) mollusc fauna of the North Bohemian Lake (Most Basin). <em>Bulletin of Geosciences.</em> 89(4), 819-908. Available for editors [request]