The importance of identified neurons in gastropod molluscs to neuroscience

[Display omitted] •Novel peptides and their roles in behaviors have been discovered.•Individual neurons can vary in their participation in neuronal ensembles over time.•The same neuron in different animals can exhibit differences in synaptic strength and gene expression.•Homologous neurons can differ in connectivity, receptor expression, and function. Gastropod molluscs have large neurons that are uniquely identifiable across individuals and across species based on neuroanatomical and neurochemical criteria, facilitating research into neural signaling and neural circuits. Novel neuropeptides have been identified through RNA sequencing and mass spectroscopic analysis of single neurons. The roles of peptides and other signaling molecules including second messengers have been placed in the context of small circuits that control simple behaviors. Despite the stereotypy, neurons vary over time in their activity in large ensembles. Furthermore, there is both intra-species and inter-species variation in synaptic properties and gene expression. Research on gastropod identified neurons highlights the features that might be expected to be stable in more complex systems when trying to identify cell types.