Introduction: Sea Urchins
Sea urchins are spiny marine organisms; many different species are found in oceans around the world. Male and female individuals produce eggs and sperm that are shed freely into seawater. Scientists have long used the urchin as a model for studying fertilization and development.

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Sea urchin embryo cell division
The first 90 minutes of sea urchin (Lytechinus pictus) embryo development. Nuclei are visible as “thumbprints” in each cell. Microtubules are faintly visible just prior to and during mitosis.

Elapsed time about 2 hours.
Sea urchin eggs were fertilized, then immediately 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.