Bivalve borings? Need more information

[Nat006]

Hello!

 

I found this rock on the beach in Romania (Eastern Europe, Black Sea). It is about 12 cm long.

 

It looks like pumice but it's actually heavy, doesn't feel like pumice at all. There are a lot of holes in it and when you look closely, you can see little seashells in the holes. 

 

In another hole, you can see something that looks like scales (You can see this in the last picture, but sometimes the order of the pictures gets messed up)

 

Any idea what all these things could be?

 

Also, is it a fossil or is it modern?

Thank you!

[Al Dente]

The larger holes look like pholad clam borings. This is a bryozoan colony at the bottom of one of the borings.

 

 

[Nat006]

2 minutes ago, Al Dente said:

The larger holes look like pholad clam borings. This is a bryozoan colony at the bottom of one of the borings.

 

 

Thank you so much! Very helpful.

 

Any idea what the "host" rock could be?

And any way to know if it's a fossil or modern?