Class IV: Six other citizens of the municipality to be appointed by the Mayor. The members of Class IV shall hold no other municipal office, position or employment, except that one such member may be a member of the Historic Preservation Commission. One Class IV member may be a member of the Board of Education. If there is an Environmental Commission, the member of the Planning Board, as required by Section I 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.