Types of Seashells

[celamllmal]

I am searching for the name of a particular shell.
It is looks like a bunch of little roundish cylinders attached one beside the other.
I have a small cluster of white ones and a larger cluster of light purple shells.
I know they are marine and that my fry and small fish love to hide in there.
Some larger fish use it to breed also. 
I always called it 'the breeding shells' but now that I want to buy additional ones...
I can't find one nor do I know what they are called!

[Vizerdrix]

I believe you are referring to barnacles.   Like the ones Mark has in his tanks, right?

[celamllmal]

Thanks!!
I posted LF barnacles on the classidied.
A.