Except as otherwise provided in this section, each trustee, independent consultant, administrative service agency and financial organization so appointed shall acknowledge in writing that it is a fiduciary with respect to all administrative or investment matters for which it has assumed responsibility with respect to a plan. Notwithstanding the foregoing, no such fiduciary acknowledgment shall be required pursuant to this section from a financial organization (a) which issues a guaranteed investment contract, or (b) which is the manager of an open-ended investment company registered under the Investment Company Act of 1940, as now in effect or as hereinafter amended, solely by reason of the investment, upon the specific direction of a trustee, another financial organization, the board, a deferred compensation committee or an administrative service agency acting in accordance with the terms of the plan to implement the investment directions of one or more participants, of amounts held under the plan in shares of such open-ended investment company.