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How does discoidal cleavage differ from superficial cleavage?

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embryos of different animals — Animal development The embryos of many animals appear similar to one another in the earliest stages of development and progress into their specialized forms in later stages.

In animal development, both discoidal and superficial cleavage are types of meroblastic (partial) cleavage, where the presence of yolk prevents the zygote from dividing completely. They differ primarily in the location and pattern of these divisions:12

Discoidal cleavage: This process is restricted to a small disk of cytoplasm located at the animal pole of the egg. Most of the yolky material remains uncleaved. This pattern is characteristic of most fishes, birds, reptiles, and monotremes (egg-laying mammals).23
Superficial cleavage: In this pattern, the entire surface layer of the egg's cytoplasm subdivides into cells, while the interior of the egg remains a central mass of uncleaved yolk. This type of cleavage is common in insects and many other arthropods.2

While discoidal cleavage results in a saucer-shaped blastodisk, superficial cleavage involves the formation of a cellular layer around the periphery of the entire egg.2