This one was more than 5 years in the making before publication in the Journal of Comparative Neurology.  Jimmy Thomson got us started, labelling neurotransmitters in the central nervous system of Hermissenda, and then Marissa Webber followed up with tons more labelling and then an amazing effort in cataloging all the labelled neurons.  Highlights were establishing that some neurotransmitters are considerably more variable between animals than others, and that one specific neurotransmitter (GABA) was not where it was supposed to be (it was missing from the statocysts – the balance organs).  You can read the (free) reprint to get our full explanation of that crazy result.  Thanks also to Roger Croll and Johnny Buckland-Nicks for help along the way.
DOI: 10.1002/cne.24286