Phylogeny of the raphidophytes Heterosigma carterae and Chattonella antiqua using 'V4' domain SSU rDNA sequences

The systematic relationships of the Class Raphidophyceae within the chromophyte algae are uncertain. The 'V4' domain small-subunit rDNA gene ('V4' domain SSU rDNA gene) was sequenced for the taxa Heterosigma carterae and Chattonella antiqua to provide characters for phylogenetic analyses. These analyses showed that the Classes Raphidophyceae and Eustigamatophyceae form a sister clade. A close systematic relationship for these two classes has not been shown before. Numerous phylogentic analyses in this study have failed to provide resolution of the deep branches of the five major evolutionary assemblages-Classes Raphidophyceae and Eustigamatophyceae; Classes Synurophyceae and Chrysophyceae; Classes Phaeophyceae and Xanthophyceae; Class Bacillariophyceae; Class Prymnesiophyceae. Transition frequency analysis shows that there is a major loss of phylogenetic signal within the chromophyte algae 'V4' domain SSU rDNA gene sequences.