Question

Spiral cleavage is found in
A)Synapta
B)Amphibia
C)Nematoda, Annelida and rotifera etc.
D)None of these

Answer 1

Hint: Single-celled zygote is the beginning of the development of multicellular organisms, to form the blastula they undergo rapid cell division therefore, the multiple rapid rounds for the division of the cell is known as cleavage.

Complete answer:
Let us study the options to find the correct answer:

Option A: Cleavage has different patterns and Synapta comes under the radial cleavage pattern as this occurs when through the successive cleavage plane, it cuts the egg straight by which the blastomeres become symmetrical in shape around the polar axis and Synapta is one of the examples of radial cleavage. Therefore, this is the correct answer.

Option B: Bilateral cleavage is also one of the cleavage patterns in which cleavage plains and spindles that are mitotic remain arranged bilaterally with the plane of symmetry which occurs simultaneously with the planned median of the embryo and amphibia is one of the examples of bilateral cleavage pattern. Therefore, this is an incorrect answer.

Option C: Spiral cleavage is that type of cleavage pattern in which around the egg axis, rotational movements of cell parts are present and, in this cleavage, it does not go in a straight direction through the egg and the blastomeres are alternate with one another and like the name suggests they are present in spiral-like tiers. Nematoda, Annelida, and Rotifera are one of the examples of spiral cleavage. Therefore, this is the correct answer.

Option D: As discussed above we have found the answer by studying the different patterns of cleavage. Therefore, this is an incorrect answer.

Hence, the correct answer is option (C)

Note: Cleavage can be done in two different patterns like meroblastic cleavage and 1)Holoblastic cleavage and which type of cleavage will be there depends on the amount of egg yolk.
2)Meroblastic cleavage - It is a type of incomplete division in which egg cytoplasm divides but the yolk doesn't
3)Holoblastic cleavage - It is a type of complete division in which the whole egg divides into distinct and individual blastomeres