The electric eel

The electric eel is an animal with electrodes on one side, and it makes a complete circuit when it touches an animal, therefore, shocking that animal. The eel looks like a snake but with gills and fins. But 2 thousand years in the future when half of the ice caps melt, the oceans will cool and start a new ice age, this could force eels to grow to be warm blooded, grow legs and become semi-aquatic. They might also get fur, like a beaver or platypus. Also they would need lungs and camouflage.