Sea urchin gastrulation has been studied for over a century. In the 1950s, the pioneering time-lapse cinémicroscopy by Tryggve Gustafson and colleagues, Richard Cloney and others revealed the dynamics of development in sea urchin embryos and other echinoderms. CLick on the micrograph below to see a (rather large!) QuickTime movie derived from one of Richard Cloney's films of PMC ingression in the sand dollar, Dendraster excentricus.
??? Mb Quicktime movie of PMC ingression in sand dollars