Any idea what’s growing on these?

[TylerReef]

Not sure what this is but two of my corals, a torch and an octi have what appears to be hard shell growing on them. I don’t know if it’s just abnormal growth or what my concern comes from them not opening as much as they were prior. On the octi it’s moving towards growing over one of the heads. Any help/advice is appreciated.

As a precaution I’ve done a coral dip and isolated them in a quarantine tank.

The tank they came out of has been running two years and these corals were added about 7-9months ago and were growing fine until now. All other corals doing well.

Thanks for any help!

 

[KrisReef]

Some kind of oyster, maybe a zigzag?