The Archaeocyatha or archaeocyathids ("ancient cups") were sessile, reef-building marine organisms of warm tropical and subtropical waters that lived during the early (lower) Cambrian period. It is beleived that the centre of the Archaeocyatha origin is in East Siberia, where they are first known from the beginning of the Tommotian Age of the Cambrian, more than 535 million years ago (mya). In other regions of the World, they appeared much later, during the Atdabanan, and quickly diversified i… (More on Archaeocyatha)