We are developing a molecular phylogeny for the suborder Sacoglossa, focusing initially on the speciose genus Elysia (>70 described species worldwide). Elysiids use a wide range of host algae as a group, but most species are host-specialized. Dispersal strategies found in Elysia include planktotrophy, with feeding larvae that are planktonic for 2-4 weeks, pelagic lecithotrophy, with pelagic larvae that swim until settling onto their specific host, and non-planktonic development, in which larvae metamorphose inside the egg mass. Elysia thus is ideal for studying causes and consequences of shifts in larval development. By mapping larval characters onto the phylogeny, we will determine how often short-lived larvae have evolved and whether maternal deposition of extra-capsular yolk is an evolutionary precursor to lecithotrophy.