Louise Page's talk addressed the role of the larval nervous system as a scaffold for the adult nervous system. To answer this question, she analyzed the phylogeny of larval development in gastropods with regards to swimming/feeding larvae compared to non-swimming/non-feeding larvae. The idea behind this analysis is that the larval nervous systems must control feeding and swimming. It appears that ancestral gastropods developed via a non-feeding larva and that feeding larvae evolved later.
Louise then went on to talk some more about the comparative development of the apical sensory organ (=apical ganglion), already mentioned in the previous talk by Roger Croll. Apical organs of most gastropod larvae contain ciliary tufts, sensory neurons, interneurons and a sensory plexus. This organ may contain receptors for the metamorphic trigger. Otherwise nobody really knows what this organ senses, speculations abound.