A viperfish has a light-producing organ on the tip of its dorsal spine. This is called a photophore, and it flashes on and off to attract prey in the deep sea.
As for sea hares, they have two chemosensory organs called rhinophores sticking up from the top of their head. They resemble bunny ears and enable the sea hare to smell, taste, and find mates.
(Bet you didn’t think I could link viperfish to sea hares, huh?)