(kinds of) small animal, like a lizard, which spends most of
its time in the water.
[ Oxford's Student's Dictionary of Current English ]

"Fillet of a fenny snake,
In the cauldron boil and bake;
Eye of newt and toe of frog,
Wool of bat and tongue of dog,
Adder's fork and blind-worm's sting,
Lizard's leg and howlet's wing,
For a charm of powerful trouble,
Like a hell-broth boil and bubble."
[ Macbeth, by William Shakespeare ]