Simple Animals: Sponges, Jellies & Octopuses
Some animals, like jellyfish and simple animals, can function without hearts, brains and other vital organs.
from Crash Course
Key Facts In This Video
A major distinction of simple animals is their tissue complexity. (0:50)
The first germ layers appeared about 535 million years ago. (5:42)
Mollusks are simple animals, yet can be very smart. (8:36)