I'd SAY an Anemone! That's one heck of a Hitch Hiker!!
Do you have any "Reef Friends" who could take it? It's going to need more light than you have on your tank buddy. Not to be mean but they LIVE from the light. They have a very slow metabolism and some people "think" they are having success with them because they live for a few months in their tanks. They just take a LONG time to slowly starve to death due to inadequate light. Yes they do eat some foods but their main source of food is the photosynthetic organisms inside of them that absorb the light and give of simple sugars which they absorb and process for energy.
PLEASE please please consider giving this beautiful creature a new home where it stands a chance of long term survival.
Good luck buddy.
Allen
