part_of part of part of embryo organ extraembryonic organ https://orcid.org/0000-0003-2569-1939 | https://orcid.org/0000-0002-7535-4407 Planarian_Anatomy Organ that is associated with an embryo and derived from the zygote from which it develops, but which does not contribute to the embryo proper or to structures that are part of the same organism after embryogenesis.