The Choanoflagellates: Heterotrophic Nanoflagellates and Sister Group of the Metazoa

INTRODUCTION Choanoflagellates are the closest living relatives of the metazoa, and the study of their cell biology and genomes promises to provide new insights into metazoan ancestry and origins. These heterotrophic flagellates are a cosmopolitan group of small, colorless protozoa that are present in marine and freshwater environments as well as in hydrated soils. Monosiga brevicollis , a marine species, has emerged as a representative of the group because it is easily grown and manipulated in the laboratory and was the subject of a recently completed genome project. Because of the similarity in morphology and ecology shown across the order Choanoflagellida, the protocols mentioned in this article should be transferable to most choanoflagellate species.