Can anyone help tell me what these are?

[MelnSteveC]

They seem to have something living in them as if I tap them lightly a white thing disappears from the opening.

Thanks in advance

 

[Crabs McJones]

They seem to have something living in them as if I tap them lightly a white thing disappears from the opening.

Thanks in advance

If you're referring to the tubes, most likely is vermedit snails. Harmless filter feeders, however, they can replicate quickly and upset corals if there is an abundance of food for them to eat. They self regulate with how much nutrients is available.

 

[Oldsalt01]

Crabs got it. Vermetids.