The following questions are based on the description below.
A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the embryo seem to be rotated 45 degrees and lie in the grooves between larger, underlying cells (spiral cleavage).
-If an undisturbed embryo is allowed to develop further, then one should expect that
A)the first opening of the gastrula will ultimately serve as the mouth.
B)upon metamorphosis, the resulting trochophore larva will gain a backbone.
C)upon gastrulation, a solid ball of cells will be produced.
D)both A and B
E)both B and C

Question

Quizplus · Accepted Answer

The spiral cleavage pattern indicates that the animal is likely a protostome, and protostomes typically have the first opening of the gastrula develop into the mouth. Therefore, option A is the best choice. Option B is incorrect because the development of a backbone requires the presence of a notochord, which is a characteristic of deuterostome development, not protostome development. Option C is also incorrect because during gastrulation in animals with spiral cleavage, a blastopore is formed, which eventually becomes the anus.

The Following Questions Are Based on the Description Below