Abstract Various evaluations of the last common bilaterian ancestor ( lcba ) currently suggest that it resembled either a microscopic, non-segmented motile adult; or, on contrary, complex segmented adult urbilaterian. These fundamental inconsistencies remain largely unexplained. A majority multidisciplinary data regarding sedentary ancestral organization is overlooked. The sedentary-pelagic mod...

A common ancestor of two vertices u, v in a directed acyclic graph is a vertex w that can reach both. A {u, v}-junction is a common ancestor w so that there are two paths, one from w to u and the other from w to v, that are internally vertex-disjoint. A lowest common ancestor (LCA) of u and v is a common ancestor w so that no other common ancestor of u and v is reachable from w. Every {u, v}-LC...