title: Solution to the phylogenetic enigma of Tetraplatia, a worm-shaped cnidarian.
abstract: Tetraplatia is a genus containing two species of pelagic cnidarians of curious morphology. Their vermiform shape and four swimming flaps are difficult to relate to the features of other cnidarians, thus obscuring their phylogenetic affinities. Since their discovery in the mid-1800s, a number of prominent cnidarian workers have weighed in on this conundrum, some arguing that they are aberrant hydrozoans and others concluding that they are unusual scyphozoans. Current taxonomic practice conforms to the latter view. However, data presented here from the large and small subunits of the nuclear ribosome leave little doubt that Tetraplatia is in fact a hydrozoan genus. Indeed, its precise phylogenetic position is within Narcomedusae, as some authors had previously deduced based on structural characters. The distinctive body plan of Tetraplatia is remarkable because it appears to have a recent origin, in contrast to the prevailing pattern of metazoan history.
authors.affiliation: NMFS, National Systematics Laboratory, National Museum of Natural History, MRC-153, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA. collinsa@si.edu
authors.forename: Allen G
authors.initials: AG
authors.lastname: Collins
authors.forename: Bastian
authors.initials: B
authors.lastname: Bentlage
authors.forename: George I
authors.initials: GI
authors.lastname: Matsumoto
authors.forename: Steven H D
authors.initials: SH
authors.lastname: Haddock
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Osborn
authors.forename: Bernd
authors.initials: B
authors.lastname: Schierwater
mesh_terms: D000818:Animals; D037402:Hydrozoa / Q000033:anatomy & histology* / Q000145:classification* / Q000235:genetics; D010802:Phylogeny; D021122:Protein Subunits / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D021122:Protein Subunits; D012269:Ribosomal Proteins