Late season tadpoles?

[Bob_A]

I've recently noticed some frog tadpoles in my pond. No legs yet. I'm in zone 5. Seems late for this to be going on.
Have any of you seen anything like this?

[dperry]

Are they large tadpoles?  Green frogs and Bullfrogs have tadpoles that are multi-year developers.  They remain tadpoles for two or three years before metamorphosis.

[Bob_A]

Maybe 2 1/2 inches long.
I get toad tadpoles every year, these are different. 
I usually buy tadpoles from a local pet store in the late spring or early summer (which I did this year). Those purchased this year have turned into small frogs.
For the past number of years I've heard the mating call of a green frog (but have never seen him), but have never gotten tadpoles from him.
He must have mated this year.

[dperry]

Yep, toad tadpoles are tiny and black.  They metamorphose into toadlets in about 5 weeks and then they are gone.  Green frogs, as you know, sound like a plucked banjo string.  Probably what you have.