From Upper Campanian strata in the SE Pyrenees (Catalonia-Spain), I’ve found this piece that defies my knowledge of the zone’s invertebrates, as neither its size nor its shape fits anything I know.
It seems an ostreid to me because the laminar structure and smooth surface of the shell, but the ostreids in the zone I’ve learned to ID, such as Amphidonte pyrenaicum, Amphidonte pliciferum, Pycnodonte vesicularis, Hyotissa semiplana, Agerostrea ungulata and Rastellum sp. are very different.
Some details:
The shell form beekite rings, as the ostreids in the