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Embryology of sea urchin: 2- cells stage

Legend:

1 blastomere (1 out of 2 daughter cells)
2 blastomere (other out of 2 daughter cells)
3 fertilization membrane
4 first cleavage plane

English name: Sea urchin
Scientific name: Psammechinus sp.
Familia: Echinidae
Classis: Echinoidea
Phylum: Echinodermata
Regnum: Animalia

Due to the equal divison of yolk over the two blastomeres, the fertilized egg undergoes a complete cleavage: holoblastic cleavage (holo = complete; blasto = germ).
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