Acritarchs are small organic fossils, present from approximately to the present. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion. Definition In general, any small, non-acid soluble (for example non-carbonate, non-siliceous) organic structure that can't otherwise be accounted for's classified as an acritarch. Acritarchs include the remains of a wide range of quite different kinds of organisms - ranging from the egg cases of small met… (More on Acritarch)