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In the developmental biology of tissue animals , the term cotyledon is the first differentiation of an embryo into different cell layers , from which different structures, tissues and organs subsequently develop. The cotyledons arise from the blastula during gastrulation .

The bilaterally symmetrical animals are triploblastic ; That is, they form three cotyledons:

The diploblastic trunks of the cnidarians and comb jellyfish form only two cotyledons .

The transformation of cells from one cotyledon into cells of another is called transdifferentiation .


  • Cleveland P. Hickman, Allan Larson, Larry S. Roberts, David J. Eisenhour: Zoology . Pearson Germany, Hallbergmoos 2008, ISBN 978-3-8273-7265-9 , pp. 245-246 .