Coelenterata Neurotransmitters

Cross references: 

Neurotransmitters in General     
    Neuromodulators in General

Catecholaminergic system in Coelenterates (PubMed)$=relatedarticles&logdbfrom=pubmed
Abstract only. 
"The catecholamine present shows similarities to noradrenalin but it is not identical with noradrenalin. Contrary to known vertebrate catecholaminergic systems, neither a reuptake system nor a degrading system is present in the coelenterate catecholaminergic nervous system." 

Biogenic Amines in Coelenterates  (PubMed) 
Abstract only.  I got the PDF from the library.   
opamine is used as an intercellular messenger in hydrozoans. The colonian anthozoan Renilla, has beta-adrenergic mechanisms in monitoring bioluminescence and serotoninergic mechanisms in rhythmic contractions.