Closing the gap: a new phylogeny and classification of the chemosymbiotic bivalve family Lucinidae with molecular evidence for 73% of living genera.

New molecular phylogenies of the chemosymbiotic bivalve family Lucinidae, using 18S rRNA, 28S rRNA and cytochrome b genes, include species from genera not previously analysed. Notable additions from Myrteinae are sequences from Rostrilucina , Solelucina and Taylorina species, species of Ustalucina , Gonimyrtea from Leucosphaerinae and additional species of Ctena , Codakia , Lucinoma and Divalucina from Codakiinae. New sequences of Lucininae include the type species of Parvilucina (P. tenuisculpta), Liralucina , Falsolucinoma , Easmithia , Jallenia , Radiolucina and Cardiolucina as well as samples of Loripes orbiculatus from multiple localities. Five major clades, defined as subfamilies, are recognized: Pegophyseminae, Myrteinae, Leucosphaerinae, Codakiinae and Lucininae. Two branches, Fimbriinae and Monitilorinae, are represented by single species. Pegophyseminae are an extremely long-branched group with a sister-group relationship to Leucosphaerinae, while Codakiinae are a sister clade to the Lucininae. In various gene trees, the position of Myrteinae is unstable in relation to Pegophyseminae + Leucosphaerinae, Monitilorinae and Fimbriinae. The Myrteinae are not well resolved, with an ambiguous correlation of molecular and morphological characters. Codakiinae now include Divalucina cumingi , shown to be related to Lucinoma rather than Divaricella and Divalinga of the Lucininae. Leucosphaerinae are a well-supported clade but morphologically disparate, with the positions of Gonimyrtea and Callucina unresolved. Several molecularly distinct subclades are recognized within the Lucininae, especially the Lucinisca , Loripes and Parvilucina groups. Parvilucina species are paraphyletic with P. tenuisculpta , the type species, distinct from the western Atlantic species. Codakia , Ctena and Pegophysema have pan-tropical distributions with former connections disrupted by vicariant events of the closure of the eastern Tethyan and Central American Seaways. Species of Radiolucina , Pleurolucina and Lucinisca are present on either side of the Isthmus of Panama. A new classification of the 96 living lucinid genera is presented, providing a framework for future studies of systematics, ecology, biogeography and bacterial symbioses. [ABSTRACT FROM AUTHOR]