Of the members of the Board first appointed, one shall hold office for the term of one year, one for the term of two years, one for the term of three years, one for the term of four years, one for the term of five years, one for the term of six years and one for the term of seven years from and after his/her appointment. Their successors shall be appointed for the term of seven years from and after the expiration of the terms of their predecessors in office. Of the alternate members of the Board first appointed, one shall be appointed for a term of one year, and one person shall be appointed for a term of two years, and all successors shall be appointed for a term of two years. If a vacancy shall occur otherwise than by expiration of term, it shall be filled by the Town Board, which shall appoint an alternate member with the longest tenure for the unexpired term.