Modes of larval development and rates of speciation in early tertiary neogastropods.

Although most warm-water molluscs have planktotrophic larval stages, some living families of tropical neogastropods are dominated by nonplanktotrophic development. Fossil protoconchs of early Tertiary neogastropods indicate that some families became progressively dominated by nonplanktotrophic development through time. This trend may be the result of higher speciation rates for nonplanktotrophs and a unidirectional trend in developmental change.