Leeches

I've seen "proper" leeches before in natural ponds, marshes etc.
However, when buying some oxygenators for our small pond, I noticed what
looked like a small transparent leech.

I *thought* I'd hosed it off the plants before the went in, but today there
were three hiding in the folds of the liner.

I managed to net them out, but wondered are they the same as the "normal"
leeches" and can I get rid of them for good ?

Peter