This Green Sea Slug (Elysia chlorotica, specifically) is the official Underwater Curiosities category challenger on Creepy Animals. We ask:
It is Underwater? Yes.
A Curiosity of sorts? Why yes.
Creepy? Most definitely.
An Animal? Hmm. Not exactly.
That’s because Elysia chlorotica creates chlorophyll, just like a plant. It accomplishes this task by harvesting the genes and photosynthesizing organelles from the Vaucheria algae it ingests. This means the slug is fully equipped to manufacture it’s own food via photosynthesis, which has never been observed in the animal kingdom. It also means that once a young slug eats its first full meal, it never has to eat the algae again.