What am I

It’s a while since we played what am I! I’ll buy lunch for the person who guesses this one.

Hint, I’m not naturally occurring, I’m man made. I go round and round in the dark and eventually I need to be replaced.

The paper clip in the photos is 1.75″ long. 

Okay….after a few guesses one was close enough. It’s the remainder of Stan’s NOTUBE Sealant after a year or so in the back tyre of my mountain bike. I had a slow leak and decided to pop off the wheel to clean it prior to resealing, out came the below sea amoeba! Go here for more info.