No clue. Ostreid?

[Quer]

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 zone are prone to do:

Two types of bryozoan attached to the shell:

 

Edited December 20, 2022 by Quer

[JohnJ]

If I had to guess, I would look more at Agerostrea ungulata as a possibility.  It has ridges similar to the related Lopha species we have in Texas.

 

[Mahnmut]

No idea on the ID, but I love those surface structures, beekite and epibionts alike!

[caterpillar]

It looks like Pycnodonte but several pieces put together

[Quer]

Thank you all for your interest.

@JohnJ, your guess made sense, as I found a complete Agerostrea ungulata nearby, this one (not a great pic, I know, it’s not fully prepared):

 

But I think @caterpillar has come closer to it. Yes, I think there are at least two specimens together (I've drawn a red line between them):

 Most important of all, following the lead I’ve found similarities with some Cenozoic Pycnodonte species, as Pycnodonte gigantica or Pycnodonte callifera.

As I am absolutelly sure the strata are Campanian, It can’t be one of those species, but at least I think I can label it Pycnodonte sp.