I agree, bullfrog tadpoles. I saw some in CA that looked like baseballs with tails and little legs. The bullfrogs were enormous, though.
By the way, if you ever get a chance to gig giant bullfrogs, go do it. Take a 12 pack of beer, a spear and a headlamp - SUPER fun. They eat good, too.
Great pictures of that woody - really, really cool.