No satisfactory definition of biological individual is currently available as consensus view among biologists and philosophers of biology. The current debate revolves around the two main distinct although partially overlapping notions of physiological individuality, based on the presence of differentiating morphological or molecular attributes, and evolutionary individuality), based instead on the unique role played by each individual in the evolutionary processes. The widespread occurrence of polygenomic organisms restricts the usefulness of the individuality criteria suggested by Pradeu (2012), i.e. uniqueness, delineation and persistence; additional problems are presented by peculiar although less pervasive phenomena such as polyembryony and chimaerism. Additionally, the persistence of individuality throughout development cannot be taken for granted, especially in the case of organism undergoing complex metamorphoses.