Question

In an eight-cell embryo of an organism, the cells of the upper tier are aligned over the cells of the lower tier at a slight angle. Which organism is it likely to be? The choices are the following: Earthworm. . . . Starfish. . . . Sea cucumber. . . . Sea urchin.

Answer 1

Answer:

Earthworm

Explanation:

Star fish, sea urchin and sea cucumber are echinoderms and exhibit radial cleavage.  The two tiers of cells of their eight cell embryo are aligned directly over each other. Earthworms are annelids and exhibit spiral cleavage during embryonic development in which upper tier of cells made an angle with cells of lower tier in eight celled embryo.

Answer 2

I think the correct answer among the choices listed above is option C. The organism described most likely is a starfish. This is because annelids and mollusks exhibit spiral holoblastic cleavage while the echinoderms have radial holoblastic cleavage.