Goniomonas: rRNA 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)-amplified small subunit ribosomal RNA gene of Goniomonas truncata was determined. Addition of the Goniomonas sequence to the eukaryotic phylogenetic tree revealed this heterotrophic flagellate to be the sister taxon of photosynthetic cryptomonads. The molecular phylogeny supports morphological 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.