is this Aiptasia ???

[Delphinus]

Ok ... if I squint reallllllly hard .... it looks like a circular blob on top of a thin cylindrical blob? Which makes me lean towards the feather duster theory ...

If you disturb them, do the crowns retreat into the cylinder?

Aiptasia would probably disappear outright, hiding into the rockwork if disturbed, since they probably have their foot hidden into holes and such.

I don't know if this helps, but, it seems to me there usually is no mistaking aiptasia as anything other than "little anemones."

I dunno.. sorry I couldn't be of better assistance..