Most marine mollusks have some form of pelagic larval stage which produces a distinctive protoconch. Scanning electron microscope studies reveal that larval shells are routinely preserved in sediments as old as the Upper Cretaceous, and that protoconchs are characteristic enough to identify to species on the basis of the unmetamorphosed larval shell. This has paleoecologic and biostratigraphic potential in cores where only a few identifiable adult mollusks are normally found. In addition, larval shells are carried by water currents to areas not inhabited by the adults, extending the species geographic range and partly eliminating facies dependence. Fossil mulluscan larvae are, therefore, a potentially valuable new micropaleontologic group.

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