Siphonophores (Cnidaria: Hydrozoa) are dominant members of the carnivorous plankton, and they are known for their ability to produce bioluminescence. Here we describe two new calycophoran species (sub-family Prayinae) that are unique in their morphological and optical traits. One species, Gymnopraia lapislazula gen. nov., sp. nov., displays a dramatic form of blue structural coloration, and the other, Lilyopsis fluoracantha, sp. nov., bears an exceptional amount of fluorescence–enough to give a greenish cast during white-light illumination. We also introduce a consistent terminology for siphonophore axes and zooids, discuss characters important for distinguishing the known prayine genera, and suggest that the presence or absence of a disjunct pedicular canal could be of diagnostic value for the group.