All members of the Planning Commission shall be appointed and approved by Council. The term of each of the members shall be for four years, or until his successor is appointed and qualified, except that the terms of the members first appointed pursuant to this chapter shall be so fixed so that on Commissions of nine members or less, not more than three shall be reappointed or replaced during any future calendar year. The Chairman of the Commission shall promptly notify Council concerning vacancies on the Commission, and such vacancies shall be filled by Council for the unexpired term.