sponge. hitchhiker?

My corals seem to close up in the evening, morning and at night. They don't just close up normally but completely. A torch will show skeleton when closed. The corals seem to close for about one minute and then try to open again. Same goes for at night because corals don't close completely at...

so I purchased some Fiji dry rock from BRS. had it stored for about three months. placed it in my new tank and lo and behold it appears that a sponge that was on the rock had rejuvenated itself and now has a siphon and appears to be growing? Is this possible? I am quite amazed.