A re-examination of siphonophore terminology and morphology, applied to the description of two new prayine species with remarkable bio-optical properties

Siphonophores are large, abundant, and ecologically important oceanic hydrozoans (Totton, 1965; Kirkpatrick & Pugh, 1984). There are approximately 160 described species, but this is a biased sample of siphonophore diversity that is skewed in favour of robust species found at shallow depths. Recent innovations in collection technology, especially the improvement of research submersibles, have revealed the existence of fragile species that have never been seen in trawls (e.g. Pugh & Harbison, 1987; Pugh & Youngbluth, 1988; Dunn et al., in press a). Here we describe two such species, Gymnopraia lapislazula gen. nov., sp. nov. and Lilyopsis fluoracantha sp. nov., which were collected by remotely operated underwater vehicles (ROVs). They are so fragile that even when successfully collected, specimens quickly deteriorated during shipboard observations, and fixation was nearly impossible. Both Gymnopraia lapislazula and Lilyopsis fluoracantha belong to the Calycophorae, a group that contains most of the described siphonophore diversity and that was found to be monophyletic in a recent molecular phylogenetic analysis (Dunn et al., in press b). Most siphonophores are bioluminescent (Haddock & Case, 1999), and many, especially calycophorans, have fluorescence and structurally based optical properties (S.H.D.H. personal observations; Mackie & Mackie, 1967). The species described herein present some of the most dramatic examples of both structural colour (G. lapislazula) and fluorescence (L. fluoracantha) yet found in the plankton.