Question

Spiral and determinative cleavage is common amongst

• A. Amphibia
• B. Annelida and Mollusca
• C. Amniotes
• D. Mollusca and Amphibia

Answer 1

The correct option is B Annelida and Mollusca

Shortly after fertilization, the zygote undergoes cleavage, a series of rapid mitotic divisions with no period of growth, during each cell cycle. The pattern of cleavage is affected by the yolk content. In spiral cleavage, after the first two divisions, the plane of cytokinesis is diagonal to the polar axis. This results in a spiral, determinative arrangement of cells, with each cell located above and between the two underlying cells. This pattern is typical of annelids and molluscs.

Thus, the correct option is (B).