ID this coral

[demonspeedn]

I've found 3 of these hitchhikers under a large coral I recently purchased. The biggest one is about 3/4" tall and has a hard skeleton with clear polyps. They seem to be growing in the month that I've noticed them. I thought maybe some type of Dendro? Any ideas?

 

[Vincent100]

Very hard to see from the pic but from what I can see you might be right with the dendro