They are invertebrates. They have radial symmetry. They are made of one segment. They have an open circulatory system.
I gave my students this multiple choice question: Which conclusion can be made about earthworms because they do not have an internal skeleton?

Only one answer is correct among these 4 choices:
- They are invertebrates.
- They have radial symmetry.
- They are made of one segment.
- They have an open circulatory system.

Could you tell me which one is correct?

They are invertebrates.