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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Still Image:
Sea urchin sperm
Sperm from the sea urchin, Lytechinus pictus.
Sea urchin sperm was diluted in seawater, then mounted between a slide and coverslip. This image was taken on an inverted compound microscope with a 40x DIC objective and digital camera.