Answer:
A tube within a tube
Explanation:
Most animals have a body plan best described as a tube within a tube. This plan calls for two openings: one for food to enter the body (mouth), one for wastes to leave the body (anus). The tube-within-a-tube plan allows specialization of parts along the tube, such as a stomach, intestine, etc. another body plan is the sax like body plan, which had only one opening. They are 10% less effective
