Odd "worm" swimming in tank at night

[RedEye1]

I found what I call a worm "swimming" in my tank last night. It propelled itself by "corkscrewing" or "spiraling" through the water.

I caught it and showed it to a coworker who hadn't seen one before. I decided to "flush it" but should have taken a photo.

I describe it as a white "worm" with faint gray stripes... black head and what appeared to be creamy / yellow pinchers as a mouth at the end of it's tiny head.

It propels itself in a corkscrew manner.
I saw one before which was half this size. This one ranged from a half inch but could elongate to about 3/4 inch.

Any ideas? If I see another I will catch it and photograph it.

 

[chocolateblnt]

sounds crazy!

 

[Lev F.]

It might be an epitoke of some other worm. Epitokes are the tail-end of a worm that contain sperm or eggs. They break off the worm and start swimming in the water coloum, until eventually they rupture, and send sperm or eggs into the water coloum, which is how some polychaetes reproduce. In the wild, it would be an epitoke soup, and then the eggs will be fertilized in that way. Chances are it was harmless, I get plenty of epitokes every night.