title: A molecular phylogeny of bivalve mollusks: ancient radiations and divergences as revealed by mitochondrial genes.
abstract: BACKGROUND
  Bivalves are very ancient and successful conchiferan mollusks (both in terms of species number and geographical distribution). Despite their importance in marine biota, their deep phylogenetic relationships were scarcely investigated from a molecular perspective, whereas much valuable work has been done on taxonomy, as well as phylogeny, of lower taxa.
  
  
  RESULTS
  Here we present a class-level bivalve phylogeny with a broad sample of 122 ingroup taxa, using four mitochondrial markers (MT-RNR1, MT-RNR2, MT-CO1, MT-CYB). Rigorous techniques have been exploited to set up the dataset, analyze phylogenetic signal, and infer a single final tree. In this study, we show the basal position of Opponobranchia to all Autobranchia, as well as of Palaeoheterodonta to the remaining Autobranchia, which we here propose to call Amarsipobranchia. Anomalodesmata were retrieved as monophyletic and basal to (Heterodonta + Pteriomorphia).
  
  
  CONCLUSIONS
  Bivalve morphological characters were traced onto the phylogenetic trees obtained from the molecular analysis; our analysis suggests that eulamellibranch gills and heterodont hinge are ancestral characters for all Autobranchia. This conclusion would entail a re-evaluation of bivalve symplesiomorphies.
authors: Department of Biologia Evoluzionistica Sperimentale, University of Bologna, Bologna, Italy. federico.plazzi@unibo.it
authors: Federico
authors: F
authors: Plazzi
authors: Alessandro
authors: A
authors: Ceregato
authors: Marco
authors: M
authors: Taviani
authors: Marco
authors: M
authors: Passamonti
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D005075:Biological Evolution; D049872:Bivalvia / Q000145:classification / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D050259:Genes, Mitochondrial / Q000235:genetics*; D049810:Genetic Speciation; D010802:Phylogeny
chemical_list: D004272:DNA, Mitochondrial