Altered frogs with eight legs - genetic damage to be sure?

Via Ed Yong on Twitter:

This August, University of Colorado-Boulder disease ecologist Pieter Johnson made a ghoulish discovery in an Oregon pond: an "octo frog," with eight hind legs. It was a particularly disturbing example of the kind of amphibian malformations Johnson has recorded in 17 states, six of them Western, since 1996.
A common, period-sized flatworm, Ribeiroia ondatrae, plays a key role in making frogs grow extra or misshapen limbs and skin flaps between joints. It breeds inside the common freshwater ramshorn snail, burrows into tadpoles' limbs, and creates cysts that interfere with development, explains Johnson. The adult frogs have trouble feeding themselves and become easy prey.

@ Altered amphibians — High Country News:

Pundit: No not mutations. And parasites and nutrients not "chemicals" dunnit.