Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 80A, § 6

The court shall, on motion of the petitioner, enter a default against all persons served with process or who otherwise appear to have seasonably received personal notice of the petition and who have not appeared and answered within the time prescribed. The court shall appoint one or more disinterested persons to act as guardian or guardians ad litem for minors, for persons under disability, and for all persons not in being, unascertained, unknown or out of the commonwealth, who have been named or described as parties respondent and for whom no duly authorized person has appeared and answered, and such guardian or guardians ad litem shall be allowed thirty days from his or their appointment to appear and answer on behalf of the persons whom he or they represent.