looks like a peice of white thread

I brought home a mushroom on a piece of rock yesterday and this morning I found a worm (?) it is about the diameter of a piece of thread, about 1/2 in long and is white. It swims freely and periodically seems to shudder or spasm. I have looked thru the stickies and don't see anything like it. Sorry I don't have a pic, but I haven't got a camera...yet.

Thanks for any help

 

Can you post a picture of it?

It could be a Spaghetti worm but they usually have more than one "thread" coming from a center point.

 

Sounds like an epitoke. When polychaetes reproduce, the last third of their body changes structure. It then falls off, swims around for a bit (very insane swimming like a spasm) and then eventually explodes or dissolves sending sperm and eggs into the water column.

 

I don't have a camera at the moment and didn't think to look at it with a magnifying glass, can't find it now. It was out when I turned the lights on.

 

Ojinsan! You got an An AquaC!! Kudos!!!