01393nas a2200133   4500008004100000020001400041245010700055210006900162260001500231520093000246100001801176700001901194856004601213       2018                        eng d  a1934-284500aAre Planaria Individuals? What Regenerative Biology is Telling Us About the Nature of Multicellularity0 aAre Planaria Individuals What Regenerative Biology is Telling Us  c2018/03/123 aFreshwater planaria (Platyhelminthes, Turbellaria, Tricladida) pose a challenge to current concepts of biological individuality. We review molecular and developmental evidence suggesting that mature intact planaria are not biological individuals but their totipotent stem cells (neoblasts) are individuals. Neoblasts within a single planarian body are, in particular, genetically heterogeneous, migratory, effectively immortal, and effectively autonomous. They cooperate to maintain the planarian body as an obligate environment but compete to make this environment maximally conducive to the survival of their own neoblast lineages. These results suggest that planaria have not fully completed the transition to multicellularity, but instead represent an intermediate form in which a small number of genetically-heterogeneous, reproductively-competent cells effectively “farm” their reproductively-incompetent offspring.1 aFields, Chris1 aLevin, Michael  uhttps://doi.org/10.1007/s11692-018-9448-9