The embryonic stage which contains a fluid-filled "segmentation cavity" is:

Explanation

The embryonic stage which contains a fluid-filled "segmentation cavity" is blastula. A blastula is an early stage of embryonic development in animals, following the morula stage. It is characterized by the formation of a fluid-filled cavity called the blastocoel. The blastula represents the next stage of development after the morula, and it is a precursor to the formation of more complex structures, such as the gastrula and, eventually, the embryo.The blastula is a critical developmental stage in the early embryonic development of animals. In some species, the blastula will undergo further changes and invaginate to form a structure called the gastrula, which is the next step in embryonic development and leads to the formation of the three primary germ layers: ectoderm, endoderm, and mesoderm. These germ layers give rise to all the tissues and organs of the developing organism. The specific details of blastula formation can vary among different animal species.