An unusual/cool place to find a fossil - Montenegro

[PRLE]

What a cool place to find a fossil.  Just returned from a holiday in Montenegro, where we spent some time in a small seaside (Adriatic Sea) town of Petrovac.  My son noticed a fossil embeded in one of the stone blocks that make up the sheltered harbor. 

 

Now, I have been coming to this town on an almost yearly basis for the last 20+ years, have walked, fished and boated out of that harbor countless times, and it took my son to spot the fossil. 

 

Anybody know what it is? 

 

If you are ever in Petrovac, Montenegro a cool little find to see.  

 

Location circled in red.  

 

 

[TqB]

Well spotted! I believe it's a rudist, an unusual type of bivalve that was common in the Cretaceous in some areas (having first appeared in the late Jurassic).
It's this type, a radiolitid, with the tabulae that make it resemble a cephalopod and some corals:

(Image from https://www.researchgate.net/figure/Schematic-structure-of-a-radiolitid-shell-showing-the-cone-shaped-lower-right-valve_fig1_365670136)

 

[PRLE]

Thanks TqB