Britannica
Sources used in this answer
Which animals undergo complete, or holoblastic, cleavage?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
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, holoblastic cleavage refers to the process where the entire zygote divides completely into blastomeres. This pattern typically occurs in eggs that contain little yolk, allowing the cleavage furrows to pass through the entire cell.12
Animals that undergo holoblastic cleavage include:
- Invertebrates: Many groups, such as coelenterates, annelids, echinoderms, tunicates, and cephalochordates.2
- Amphibians: These also exhibit holoblastic cleavage, though the resulting blastomeres vary significantly in size due to the distribution of yolk, with smaller cells at the animal pole and larger, yolky cells at the vegetal pole.2
- Mollusks: Many species within this group also follow this pattern.2
In contrast, animals with large amounts of yolk, such as birds, reptiles, and most fishes, typically undergo meroblastic (partial) cleavage, where only a portion of the egg cytoplasm divides.12