Article: Observations on the nature of the acritarchs [The Fifteenth Annual Address, delivered March 1972]

Recent studies of the acritarchs have shown that many have features in common with one or other of two major groups of planktonic algae—the prasinophyceae (tasmanitids) and the dinophyceae (dinoflagellates). However, studies of the ultrastructure, excystment mechanisms, and knowledge of their geographic and historical distribution are too incomplete at the moment to allow a worthwhile natural classification of the 300 or so acritarch genera. A rough outline of their evolution can, however, be indicated, and shows a marked diversification in the Lower Cambrian and a more rapid succession of groups through the Lower Palaeozoic.