What is this? Should I be worried?

[F.H]

Is it a tiny ball anemone?

[ReefGrrl]

Thanks for the suggestion - I wondered about that - I have lots of orange ball anemones all over the place and their tentacles are kind of thready and translucent with opaque white balls on the ends.

This little thing had short-ish knobbly opaque appendages of varying lengths. It appeared to be stuck to the glass by the body, and was holding the piece of seaweed in a couple of the appendages.