Metazoans comprise all of what are commonly referred to as animals.
None are capable of creating their own food directly from inorganic substances. In the last few years a considerable amount of phylogenetic data notably from mitochondrial DNA has emerged, significantly improving current understanding of metazoan relationships. The accuracy of mitochondrial genetic clocks has also been increasingly called into question, further complicating the issue. Colonial Theory is the most popular current theory of metazoan origination, and holds that metazoans are derived from a colony of flagellated unicellular organisms. The Choanoflagellate class of protozoa are the most likely candidates for precursor organisms.