GONIOMONAS - RIBOSOMAL-RNA SEQUENCES INDICATE THAT THIS PHAGOTROPHIC FLAGELLATE IS A CLOSE RELATIVE OF THE HOST COMPONENT OF CRYPTOMONADS

The nucleotide sequence of the polymerase chain reaction (PCR)-amplifi ed small subunit ribosomal RNA gene of Goniomonas truncata was determi ned. Addition of the Goniomonas sequence to the eukaryotic phylogeneti c tree revealed this heterotrophic flagellate to be the sister taxon o f photosynthetic cryptomonads. The molecular phylogeny supports morpho logical data suggesting that Goniomonas diverted from the cryptomonad lineage prior to their acquisition of a plastid through endosymbiosis of a eukaryote. Goniomonas, which is phagotrophic, may thus represent an extant relative of the host component of cryptomonad algae.