Which of the following is a feature of the "tube-within-a-tube" body plan in most animal phyla?
A) The outer tube consists of a hard exoskeleton.
B) The outer tube consists of digestive organs.
C) The mouth and anus form the ends of the inner tube.
D) The two "tubes" are separated by tissue that comes from embryonic endoderm.

Question

Quizplus · Accepted Answer

In the "tube-within-a-tube" body plan, the mouth and anus form the openings at the opposite ends of the inner tube. This allows for a unidirectional flow of food and waste through the digestive system, which increases efficiency in nutrient absorption and waste removal. The outer tube may consist of other organs and tissues, such as muscles and reproductive organs, but it does not necessarily have to be digestive in nature. Additionally, although many animals with this body plan do have an exoskeleton or endoskeleton, it is not a required feature. Finally, the two "tubes" are indeed separated by tissue that comes from embryonic endoderm (the innermost germ layer).

Which of the Following Is a Feature of the "Tube-Within-A-Tube