Question

In spiral cleavage, planes are

• A. Vertical
• B. Horizontal
• C. Subequatorial
• D. Oblique

Answer 1

The correct option is D Oblique

On the basis of arrangement of blastomere cleavage is of four types:

(1) Radial cleavage - in this cleavage, divisions are at right angle to the earlier and formed equitorial plane. So, that cells are placed just one above the other. For example Deuterostomia animals, Echinodermata, Chordata.

(2) Spiral cleavage - in this cleavage, planes are oblique. In this cleavage, four blastomere of lower plane rotates in opposite direction to the upper surface and forms oblique planes. For example Mollusca, Helminthes (Aschelminthes and platyhelminthes), Annelids.

(3) Bilateral cleavage - in this cleavage bilateral symmetry is established by the unequal division. For example Amphibia, Tunicata (Urochordata), Cephalochordata animals.

(4) Biradial cleavage -in this cleavage blastomere cell divides in such a way that, four central blastomere are large and four blastomere are small. For example Ctenophora.

Thus, the correct answer is option D.