Cell fate determination during development requires a complex mix of inherited and external signaling cues. An ideal framework to examine fate determination is spiral cleavage, the ancestral form of cleavage for Spiralia (~Lophotrochozoa). Animals with spiral cleavage undergo stereotypic cell divisions, and each cell (blastomere) reproducibly produces a specific set of tissues—an ideal situation to study inherited signaling cues because cell fates are known in advance. By removing potential signaling cells we can determine if their external signals are necessary for a specific developmental fate (conditional specification). If the specific end fate is still produced, this suggests that only inherited signals are necessary (autonomous specification). Recently it was determined that the head neural tissue was autonomously specified in the sedentary annelid Capitella teleta. Intriguingly, trunk neural tissue was not, suggesting that the brain and VNC may be controlled by different and independent genetic signaling modalities. Here we used blastomere isolations to test for autonomous or conditional neural specification in the gastropod Crepidula atrasolea and the errant annelid Platynereis dumerilii. Our results will help us determine whether separate signaling modes driving head and trunk neural development is unique to C. teleta or is a widespread phenomenon in spiralians. If it is widespread, then this would support a deep homology in spiralian central nervous system (CNS) development. If there are differences in how neural fate is specified in these three groups, this could indicate that evolution of developmental programs in the context of the highly conserved spiral cleavage program is more labile than expected. Alternatively, this may suggest that the CNSs of these groups are not fully homologous.