Sea Star and Mollusk, Satonda Island, 2005

Many mollusks, like this ridged specimen resting atop a blue sea star (starfish) near Indonesia's Satonda Island, are commensal creatures, meaning they benefit from living on or near a host organism, while leaving the host largely unaffected. However, mollusks are also a favorite prey of sea stars, which use their suction-cupped tube feet to pry open clams, mollusks, and oysters before consuming their innards.

(Photo shot on assignment for, but not published in, "One Fish, Two Fish, Red Fish, Blue Fish: Why Are Coral Reefs So Colorful?" May 2005, National Geographic magazine)

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