I thought it was poop but it wouldn't blow off. It's not hard like a tube worm in that it doesn't break but it's attached. I pulled the rock an scraped it off and superglued over the hole figuring that would work. The second dot of glue was to cover a hole that looked similar. Couple days later and here it is again.
Before I messed with it
After glueing the holes
Coming out after being glued
Before I messed with it
After glueing the holes
Coming out after being glued



