5. No body cavity to a body cavity with muscle lined organs or coelom. A coelom allows for internal organs to operate independently of each other. Cardiac muscle squeezes heart independently of muscle moving food through the digestive track.
Primitive characteristic More recently evolved characteristic
One tissue layer or ______________ or______________
_____________ ______ or _______ _____________and bilateral symmetry
No body cavity or _______________________
Water habitat or _______________________
_______________ _________ or “tube within tube” body
No head region or _____________________