little thing on my live rock

[Spanky]

odd shaped roundish thing. seems may be sticky as on close inspection seems to have a pellet stuck on it from earlier feeding of fish. wasn't there little while ago seems to appeared out of no where. doesn't look to have eyes or mouth. atleast not from what i can see. tank is stable ph 8.2 ammonia, nitrite, nitrate all 0's. any idea what this odd thing is?

 

[Soukup31]

Maybe a sponge

 

[Spanky]

thats what i was thinking. but then it disappeared. don't think a sponge can move can they? could it be possible a piece of my anenome broke off an it could be growing into another anenome?