Science Homework Help

I’m working on a biology question and need an explanation to help me understand better.

Which of the following best describes the development of the mesoderm during sea urchin gastrulation?

Group of answer choices

Cell differentiation along the future mouth.

Cell differentiation around the outer surface of the blastula.

Cells crawling over the inner surface of the blastula and differentiating.

Invagination of the epithelial cells that form the blastula.