Thecacera pacifica is a nudibranch or “sea slug” that looks alarmingly and endearingly like the most famous of all Pokémon pocket monsters, Pikachu! The resemblance is so, er, shocking that it's likely Pokémon franchise creator Satoshi Tajiri based his original concept of Pikachu on this small, colorful nudibranch native to the warm waters off the coast of Japan.
Nudibranches are shell-less marine molluscs that often display brilliant and contrasting colors. There are about 2,300 species of nudibranch, some of which recycle stinging cells acquired from their meals of jellyfish as a defense mechanism. There are no electric sea slugs, however... not in real life, anyway.
Thecacera pacifica rose to fame shortly after Pokémon became a cultural phenomenon, as marine biologists who were familiar with the species were struck by its remarkable resemblance to Pikachu. Today, the species is informally known as the “Pikachu Sea Slug”.
If you're thinking about popping down to your local pet store and introducing a Pikachu Sea Slug or two to your living room aquarium – admit it, the thought's crossed your mind – well, think again.
While nudibranches aren't generally endangered (though individual species may vary in rarity), they're finicky creatures that are difficult to feed. Nope, “Sea Slug Chow” just ain't gonna do it. They can also exude toxic secretions when stressed, which won't be appreciated by your aquarium's other residents.