Classroom Explorations: Model Organisms
Early development in a sea urchin (Lytechinus pictus) embryo illustrates how a single egg develops into a hollow blastula. In urchins, blastula hatch out of their eggshells to become free-floating marine organisms. (The elapsed time is about 18 hours.)
Sea urchin eggs were fertilized, then mounted in seawater between a slide and coverslip (using a silicon spacer). Images were taken at room temperature on a compound inverted microscope using a 40x DIC objective and digital camera.