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Embryology of sea urchin: 16-32 cells stage

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1 unqual blastomeres

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

The orientation of the cleavage planes is not anymore so symmetrical, so that smaller and larger blastomere are formed. Depending on the cell size, these blastomeres are called micro-, macro- en mesomeres: 4 micromeres at the vegetal pole, surrounded by 4 macromeres, plus another 8 mesomeres at the animal pole.
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