When Rudolf and Elizabeth Raff go to Australia, it's for the wildlife. But they're not interested in koalas and kangaroos. The two biologists from Indiana University take an intense interest in two similar, yet distinct, species of sea urchin.

Sea urchins are members of the echinoderm family, making them close relatives of starfish. Five-sided and roundish, they range in width from a quarter-inch to six inches. "They're basically a limestone box full of gonads with spines on the outside," Rudolf Raff says.

Over the past century, experiments on sea urchins have helped demonstrate how ...

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