Strange worms, identification needed

[Fento]

Hi! One friend of mine has some strange worms at his tank. He says they doesn't seem harmfull for shrimps, but he's kind of worried about his crs. He said they use to be swinging with water stream, but if they got scared they hide under the gravel.
Does anybody know what kind of worms are these? Are they dangerous? How do they arrive to the tank?

http://img36.imageshack.us/img36/5260/10182396.png

http://www.youtube.com/watch?v=MbckOkxAiWk

both (video and picture) copyright is from Mario Gonzalez (guela) I was given permission to post them here.

[Alfa Shrimps]

Hello.
Maybe Lumbriculus variegatus:
http://aquaesfera.org/panel/showthread.php?2668-BlackWorm-...
Regards.

[Fento]

Thank you Alfashrimp :)
I've asked my friend for details and it seems it's at least a Lumbriculus (not sure about the specie).
It's an interesting worm.

[Summit MicroFarm]

Fento,
These worms are excellent to condition breeding fish...If you can find a clean source of these worms they can be extremely useful. :smile:

:alien: