Assertion: echinoderm's cell | /r/HasProperty | blastula
Facets:
Source sentences:
text: During indirect development, the fertilized egg divides many times to produce a hollow ciliated ball of cells (blastula); cleavage is total, indeterminate, and radical.
text: As the hollow sphere of cells known as a blastula develops, an invagination produces an opening called the blastopore.