Peculiar tube-like bivalve with densely packed concave tabulae (Štramberk Limestone, Tithonian-Berriasian)

Abstract

The fossils described here are from the Tithonian-lower Berriasian Štramberk Limestone of the Czech Republic. The specimens consist of densely packed, straight to slightly curved short tubes. Each tube is composed of a single valve rather than two valves. Some tubes show constrictions in the wall, generally on just one side. The lumen is almost completely filled with numerous densely packed slightly to strongly concave tabulae. In some tubes, the tabulae form complete internal floors while in others they connect to the wall with another tabula or seal the concavity in the underlying tabula. The tubes somewhat resemble tubeworms, rudists, vermetids and calcareous algae. However, based on morphological similarities such as the tube-like morphology in longitudinal section and the shapes of the lamellae and tabulae, these tubes resemble oysters described from the Albian of Brazil. Accordingly, we infer that the Štramberk tubes represent oysters or oyster-related bivalves.