Class IV: other citizens of the municipality, to be appointed by the Mayor or, in the case of the Council-Manager form of government, pursuant to the Optional Municipal Charter Law, P.L. 1950, c. 210 (N.J.S.A. 40:69A-1 et seq.) or the Municipal Manager Form of Government Law (N.J.S.A. 40:79-1 et seq.), by the Council, if so provided by the aforesaid ordinance. The members of Class IV shall hold no other municipal office, position or employment, except that, in the case of nine-member Boards, one such member may be a member of the Historic Preservation Commission. No member of the Board of Education may be a Class IV member of the Planning Board, except that, in the case of a nine-member Board, one Class IV member may be a member of the Board of Education. If there is a Municipal Environmental Commission, the member of the Environmental Commission who is also a member of the Planning Board, as required by § 1 of P.L. 1968, c. 245 (N.J.S.A. 40:56A-1), shall be a Class IV Planning Board member, unless there is among the Class IV or alternate members of the Planning Board both a member of the Historic Preservation Commission and a member of the Board of Education, in which case the member common to the Planning Board and Municipal Environmental Commission shall be deemed a Class II member of the Planning Board. For the purpose of this section, membership on a municipal board or commission whose function is advisory in nature and the establishment of which is discretionary and not required by statute shall not be considered the holding of municipal office.