. Definition In general, any small, non-acid soluble (for example non-carbonate, non-siliceous) organic structure that can not otherwise be accounted for is 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 metazoans to resting cysts of many different kinds of chlorophyta (green algae). It is likely that some acritarch species represent the resting stages (cysts) of algae that were ancestral to… (More on Acritarch)