How can animals not have brains?

Question

I know that the groups prifera, cnidaria, ctenophora and chordata (cephlachordata) do not have brains but how exactly do they function then. What kind of nervous system do they have?

Answer 1

porifera -- none!
http://www.earthlife.net/inverts/porifera.html

Link explains it all.

cnidaria -- "7. Nervous System - Nerve Net
a. Anastomosing network of nerve fibers
b. Mostly in epidermis (connects to gastrodermis)"

http://zoology.muohio.edu/crist/Zoo312/Cnidaria.html

Just search on the name & "nervous system" and sites will come up with the information you need.