The Urmetazoan is the hypothetical last common ancestor of all animals, or metazoans.
It is universally accepted to have been 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.
[1] All animals are posited to have evolved from a flagellated eukaryote.
Molecular studies place animals in a supergroup called the opisthokonts, which also includes the choanoflagellates, fungi, and a few small parasitic protists.
The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella instead.