Marine Sponge
(Varies by Species)

Found in oceans across the world, the Marine Sponge is one of the simplest animals on Earth — it has no brain, nervous system, muscles, or organs of any kind, yet it is alive.

Perhaps most remarkably, if two compatible sponges are broken apart and their cells mixed together, those cells will actively seek out their own kind, sort themselves back out, and reassemble into their original separate individuals — a feat of biological self-organization that continues to baffle scientists!