Each health care provider served with a claim shall file with the Director a response to the claim and any third-party claim within the time specified in the Maryland Rules of Procedure, with copies to all interested parties, including the chairman. A filing fee of $25 is to accompany an initial response or other pleading. The entry of subsequent counsel or other pleadings is without charge. A response may state that the controversy falls within one or more particular recognized specialties. A third-party claim shall be filed with the Director within 30 days of the response unless a later filing is agreed to by the parties or is allowed by the chairman or the Director. Unless the defendant does not dispute liability, a certificate of a qualified expert and a report of the attesting expert shall be filed with the Director within 120 days from the date the claimant filed and served each defendant with a copy of claimant's certificate.