Archaeocyatha (/ˈɑːrkioʊsaɪəθə/, 'ancient cups') is a taxon of extinct, sessile, reef-building[2] marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period.

It is believed that the centre of the Archaeocyatha origin is now located in East Siberia, where they are first known from the beginning of the Tommotian Age of the Cambrian, 525 million years ago (mya).

This means that the fossils cannot be chemically or mechanically isolated, save for some specimens that have already eroded out of their matrices, and their morphology has to be determined from thin cuts of the stone in which they were preserved.

As for the earliest archaeocyathan, the Ediacaran sponge Arimasia from the Nama Group may be within the clade and specifically allied with Monocyathea, however this is unclear.

Their widespread distribution over almost the entire Cambrian world, as well as the taxonomic diversity of the species, might be explained by surmising that, like true sponges, they had a planktonic larval stage that enabled their wide spread.

Radiocyatha and Cribricyatha were two diverse Cambrian classes comparable to Archaeocyatha, alongside genera such as Boyarinovicyathus, Proarchaeocyathus, Acanthinocyathus, and Osadchiites.