Worms in my daphnia tank?

[thedavidzoo]

I've had the daphnia for a month or 2. They are hanging in there although there isn't a heater in the tank.
Anyway, while siphoning out some of the scum, I noticed several small worms. They are much bigger than microworms, pinkish white, 1/2-1 cm long and very skinny.
Anyone know what these are and where the heck they came from? Also, are they safe to feed the fish or is it some kind of parasite, yikes?

 

[Grundsau]

I feed them to my fish. They eat them up.