Ablastula is
a. a digestive organ
b. the innermost germ layer
c. a layer of embryological tissue
d. a hollow ball of cells in an embryo

d. a hollow ball of cells in an embryo

Explanation:

Blastula is a stage during early embryo development which arrives between morula stage and gastrula stage. This stage is characterized by a hollow ball of cells which surround a cavity known as blastocoele. This layer of cells which surround the blastocoele is known as blastoderm and it is formed by the repeated cleavages of zygote (fertilized egg). This cavity inside blastoderm i.e.  blastocoel is filled with fluid. Soon after the blastula develops fully, it turns into a gastrula and the process is called as gastrulation.

[content deleted] - user123802726recklesschicken

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.