There shall be a complaint and an answer; and there shall be a reply to a counterclaim denominated as such; an answer to a cross-claim, if the answer contains a cross-claim; a third-party complaint, if a person who was not an original party is summonsed under the provisions of Rule 14; and there shall be a third-party answer, if a third-party complaint is served. No other pleading shall be allowed, except that the court may order a reply to an answer or to a third-party answer.