Diploblastic Metazoans: Porifera and Archaeocyatheans
These two groups have frequently been considered together in the same phylum as simple forms of metazoans. The affinities and taxonomic position of the exclusively fossil archaeocyatheans has long been discussed. However, sponges and archaeocyatheans are now interpreted as two separate metazoan phyla which originated directly but independently from protozoan ancestors. The receptaculids, another enigmatic group, is placed close to these two groups, albeit in a still rather uncertain position.
KeywordsSiliceous Calcite Cretaceous Sponge Jurassic
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