re creature I found in the dark
 

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.

how fast did it move? could be a mantis?

Since you described it as "caterpillar" like in appearance, I'd say it's probably a type of bristle worm. You'd have to catch it to properly ID it.

it moved very quickly. Hmm bristle I dunno. Possible I guess.

Moved quickly? Eunicid worm is my bet.

Good hunch,that was my gut instinct, could be a number of other worms though.

Good, bad or indifferent?

Could be any one of the above. Monitor your livestock and make sure things aren't going missing, if they are....get it out!

Okay, I am hearing some clicking coming from in there, never heard it before and have
added nothing new to tank. Hmm

Clicking is usually a sign of a Mantis. Well that or a Pistol Shrimp.