Complex sentence: The pelagic veliger larvae then hatch, persisting in the water column for 14 to of 80 days, feeding primarily on plankton, and eventually settle on the ocean floor where they develop into hard-shelled snails.
Split into simpler sentences: The pelagic veliger larvae (a larval form common to various marine and fresh-water gastropod and bivalve mollusks) then hatch, persisting in the water column for 14 to of 80 days and feeding primarily on plankton. They eventually settle on the ocean floor where they develop into hard-shelled snails.