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March 25, 2013
Scanning electron microscope image of Strongylocentrotus drobachiensus [sea urchin] embryo at the late gastrula stage. Embryo was cut to reveal blastocoel cavity. The fertilization envelope dissolves during swimming blastula stage; therefore, the cilia and microvilli can be seen on the outer epithelial layer. The primary mesenchyme cells have formed a syncytial ring, which is the precursor to spicule formation(developing calcareous larval skeleton). A portion of the archenteron can also be seen. Class Echinoidea Superorder Echinacea Order Echinoida Strongylocentrotus drobachiensus JEOL 35C SEM Credit: Louisa Howard

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