Weird creature

Question
There is some kind of strange white-ish round creature adheared to a rock in my aquarium.  It moves slowly by lifting up this umbrella like covering and extending two tenticles (or so they seem).  It appears to have a small hole at the top of the "umbrella."  What could this thing be?

Answer
Carrie,
I'll be honest, without being able to see what you are talking about I'm not entirely sure what it could be.  However, it sounds like it could be some sort of crab or other invert that came in on the live rock.  White?  Sounds like it might be juvenille and colorless at this time.

If it doesn't seem to be bothering anything, I'd leave it alone.

It's never a bad idea to have some reference books around for when these types of things turn up.  I suggest you pick up a copy of Julian Sprung's Invertebrates: A Quick Reference Guide book.  I think we're offering some sort of shipping discount on it right now via our online catalog at www.aquariumcrazyfish.com

Thanks for your time and best of luck with your tank!

Regards,
Scott Johnson
Aquarium Crazy Fish
www.aquariumcrazyfish.com