crab = cangrejo
oso = bear
firefly = luciérnaga (luciérnaga=libélula=bichito de luz ¿?¿?)
mosca = fly
iguana = lizzard - not so sure about this one
cocodrilo = alligator
burro = donkey
murciélago = bat
serpiente = snake
paloma = dove
lion = león (that's a difficult one...)
tiger = tigre
cougar = puma
leopard = leopardo
wolf = lobo (the plural is, of course, wolves)
Those are all I can think of right now.
Good luck!
EDIT: I tried to post before, but the server went into bastard_mode and wouldn't let me...