What is this creature?

[Vmacisback]

Help....Seems like its eating away the bottom of a large cyphastrea colony i have that has grown about the size of a softball. I turned it over one day and thought it was a small anemone but it has since tripled in size and my coral will no longer encrust from the base.

 

[Eckolancer]

No idea but following

 

[Pete polyp]

Bump!

 

[TheChef]

colonial tunicate

pretty one too! completely harmless unless its something like T. solidum, which will grow quick enough to smother things