What are these in my tank?

[shirleymunro]

In my tank today when I did partial water change and cleaned out filter were several "creatures" that were green about half an inch long and very thin, looked a bit like a piece of plant like cabomba but were definately swimming!!!!

 

[canarsie11]

 

[Arfie]

I saw something similar in my tank this week after I moved some gravel whilst doing a gravel vac, it was like a small piece of wiggling cotton, once it went in my bucket I couldn't find it again for a closer look.

Arfie