Echinoderms - Fertilization

Fertilization of L. pictus and S. purpuratus eggs. Image from movie courtesy of the Exploratorium.
One of the hallmarks of fertilization is that it is species-specific: sperm from one species cannot or usually do not fertilize eggs of another. Sea urchins have been studied extensively in this regard. In the movie shown here, L. pictus sperm are used to attempt to fertilize both L. pictus and S. purpuratus eggs. Successful fertilization can be followed by observing the formation of the fertilization envelope. See if you can determine which type of sperm was used to fertilize the mixture of eggs!