Apparently having a brain and a central nervous system isn't essential to animal life at all levels. How do they exist?

Touche mom! This question arose because on another thread an Answermugger informed me that some living "animals" don't have a brain or nervous system. I guess I figured even microbes have them. But I'm having a hard time understanding how that can be true. It's just a blob of protoplasm? How do they know how to keep alive, eat, protect themselves or are all of those things at too high a level?  Thank you for your reply! :)

Maybe you can research sponges, barnacles, and jellyfish. I'm too lazy to look it up but maybe some sites can help you understand how they work. Maybe it's just the earlier animals that don't have a brain/nervous system but they managed to survive all this time just the way they are so they must be doing something right.

Thank you for your reply Patch.