This talk by Roger Croll was all about the developing nervous system in gastropod larvae. Many developing invertebrates including most gastropod larvae have a so-called apical organ. This organ appears to contain serotonergic and FMRFamide-containing neurons, sits over the cerebral commissure, appears first after 12h of development and is not organized into any of the ganglia.
The talk continued to outline the development of FMRFamide cells in various stages of Aplysia larval development. This was then followed by the development of catecholaminergic cells in several other gastropod larvae. FMRFamide and apical neurons are lost during metamorphosis, while some catecholaminergic neurons survive metamorphosis. These broad developmental rules appear to be conserved across mollusks. Their function appears to be conserved as well: the neurons appear to mostly control muscles and ciliate cells (i.e., their beat frequency).