Defining the properties and characteristics of the last common ancestor of bilaterian animals, Urbilateria, is a key question of the evolution and development field (1). (scienceintheclassroom.org)
Ancestral state reconstruction suggests that contractile mesodermal midline cells existed in bilaterian ancestors. (scienceintheclassroom.org)
Bilaterian origins: Significance of new experimental observations. (eol.org)