One of the features that made sea urchins a popular model system was the ability to shed gametes into the sea water after intracoelomic injection of potassium chloride (KCl). The animated GIFs on this page are courtesy of Dr. David Epel at Stanford University's Hopkins Marine Station. His web site is located at http://www-leland.stanford.edu/~depel. In the case of eggs, the coelomic injection results in release of eggs from the gonopore; the animal is inverted over a beaker of sea water, and the eggs are released into the beaker. On the right, sperm are directly aspirated from the gonopore.
Animations of spawning sea urchins (courtesy of Dr. David Epel, Hopkins Marine Station).
To see a more detailed internal view of coelomic injection, click the picture below to access a QuickTime movie derived from an animated GIF courtesy of Dr. David Epel.
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movie: 150 K