A sloth's fur is its own tiny ecosystem, complete with a resident species of algae

Sloths move so slowly that algae grow directly in grooves in their fur, tinting it green and helping camouflage them in the canopy. Moths and beetles that live nowhere else spend their whole lives in that fur too, feeding the algae with their waste in a miniature symbiosis found on no other mammal.

— Wikipedia contributors, Sloth — Fur ecosystem and algal symbiosis