<prompt> Sacral-teratomasacrococcygeal teratoma is a derivative ofPrimitive streakEctodermHypoblastsCranial neuropore  <response>: Ans: A Primitive streakRef: Textbook of Human embryology 8the p.671Gastrulation Hensens node:In 2nd week - Gastrulation occurs --- Establishes 3rd germ layer mesoderm.Gastrulation begins with primitive streak formation in caudal region of epiblast.Primitive node or Hensens node or primitive knot:Thickening formed at cranial end of primitive streak.Sacrococcygeal formation:Failure of Hensens node to regress can lead to sacrococcygeal formation.Incomplete primitive streak regression - leaves caudal remnant - Sacrococcygeal teratoma.Arise from residual to totipotential cell rests Hensens node.Sacrococcygeal teratoma demonstrates tissue derived from all three cell layers.Contain varying propoions of mature immature elements. 