Urmetazoan
THE HYPOTHETICAL LAST COMMON ANCESTOR OF ALL ANIMALS
Urmetazoon; Placula; Gastraea; Phagocytella; Bilaterogastraea; Gastraea theory; Urmetazoa
The Urmetazoan is the hypothetical last common ancestor of all animals or metazoans. It is universally accepted to be a multicellular heterotroph — with the novelties of a germline and oogamy, an extracellular matrix (ECM) and basement membrane, cell-cell and cell-ECM adhesions and signaling pathways, collagen IV and fibrillar collagen, different cell types (as well as expanded gene and protein families), spatial regulation and a complex developmental plan, and relegated unicellular stages.