re creature I found in the dark

[Leah]

This morning I just happened to get a glimpse of something dark in my tank,
I had just turned on a night light and just peaked in and to my wonderous
eyes saw something scoot into a tiny hole in the rock I am guessing maybe
half an inch with tentacles and maybe a small head looks almost fuzzy. I
can see it sticking out a bit from the hole. What could it be? If I didn't know
better I'd say it was a catapillar. Looks black to me.