Tube-within-a-tube body plan is shown by

• a. Coelenterates
• b. Platyhelminthes
• c. Aschelminthes (Nemathelminthes)
• d. Porifera

The tube-within-a-tube body plan is characteristic of certain animal groups. Among the options provided, the correct answer is:

Correct Answer

c. Aschelminthes (Nemathelminthes)

Explanation

This body plan features an inner tube (the digestive tract) surrounded by an outer tube (the body wall). It is a significant evolutionary advancement that allows for more complex body structures and functions.

Other Options

• a. Coelenterates: These organisms, like jellyfish, have a simple body plan with a single opening.
• b. Platyhelminthes: Flatworms exhibit a flat body structure without a true body cavity.
• d. Porifera: Sponges have a porous body and lack a defined body plan.

Understanding these distinctions helps in studying animal evolution and diversity.