All moneys received by or belonging to the plan shall be paid to the executive director and promptly deposited by the executive director to the credit of the plan in one or more banks or trust companies or other financial institutions as selected by the board. No such money shall be deposited in or be retained by any bank or trust company which does not have on deposit with and for the board at the time, the kind and value of collateral required by sections 30.240 and 30.270, for depositories of the state treasurer. These moneys are funds of the plan and shall not be commingled with any funds in the state treasury. The executive director shall be responsible for all funds, securities, and property belonging to the plan and shall be provided with such corporate surety bond for the faithful handling of the same as the board shall require.