Difference between Blastula and Blastocyst

What is the difference between Blastula and Blastocyst?

Blastula as a noun is an early form in the development of an embryo, consisting of a spherical layer of cells filled with fluid; a blastosphere. while Blastocyst as a noun is the mammalian blastula

We hope you now know whether to use Blastula or Blastocyst in your sentence.