Got loads of live rock off ebay, came with LOADS of this attached, hope (praying) its all good and not some strange form of aptasia, please let me know. Thanks in advance
They're majano anemones. Not quite as bad as aiptasia, IMO, but not something I'd keep either. They will reproduce and can start to take over if allowed to do so.
I'd keep them only if I never wanted a reef. Otherwise, I'd remove them and shoot the seller a note asking why they didn't disclose they had pest infected rocks.