Morgan Stanley’s top investment banker joined the ranks of high-level executives departing the embattled Wall Street firm yesterday, while the company’s board of directors told a group of dissident shareholders it has full confidence in the chief executive, Phil Purcell.

Joseph Perella, a star of investment banking for more than two decades, will leave his job as head of Morgan Stanley’s investment banking operations, according to the company. Morgan Stanley did not give a reason for his departure.

Mr. Perella, 63, is the latest in a string of high-level executives to leave Morgan Stanley amid a controversy over its lackluster performance under Mr. Purcell. Tarek “Terry” Abdel-Meguid, 49, Perella’s deputy, also left the company, Morgan Stanley confirmed. The two will remain on during an unspecified transition period, the company said.

Two other executives, Michael Uva and Cordell Spencer, will take over as co-heads of investment banking.

Meanwhile, in a letter to the eight leaders of the dissident group, the 10 non-executive members of Morgan Stanley’s board urged the group to stop its attacks on the company.

“The Board of Directors has considered each of your communications,” the board wrote in the letter, made available by the company. “We have full confidence in Phil Purcell and the strategy that management is pursuing. We are carefully monitoring the performance of Morgan Stanley.

“It is clear to us that your ill-considered, professionally directed attacks on Morgan Stanley and our people are damaging the firm and our shareholders,” the letter continued. “We ask you to desist.”

A spokesman for the dissident group issued a statement in which the former executives attacked the board for its “failure to understand the crisis of confidence in the leadership of the firm’s CEO, and shareholders’ continuing disappointment in the firm’s performance. “The group also called the departure of Perella and Meguid “a sad day for the firm.”

Shares of Morgan Stanley fell $1.35, or 2.48%, to $53.13 on the New York Stock Exchange. The stock has traded between $46.54 and $60.51 over the past 52 weeks, but has dropped nearly 8% since April 4.

The latest resignations, first reported in the Wall Street Journal, come as Morgan Stanley wrestles with the departure of other top executives, including former President Stephan Newhouse, and top investment executives Vikram Pandit and John Havens. The latter three resigned after Mr. Purcell removed Mr. Newhouse as president, replacing him on March 28 with co-presidents Zoe Cruz and Stephen Crawford, both of whom also have been added to Morgan Stanley’s board.

With the departure of Perella and Meguid, five of the 14 members of the company’s management committee have resigned within the last three weeks. The five, which include Newhouse, Pandit and Havens, represent five of the top six spots in Morgan Stanley’s investment banking division.

The latest departures will likely lend credence to the dissidents who have called for Mr. Purcell to be fired or resign, saying his policies are causing a “brain drain” as top people leave the firm in protest. The dissidents have claimed Mr. Purcell has rewarded his loyalists at the expense of more qualified executives.

The group seeks to supplant Mr. Purcell with former President Robert Scott as CEO and an unnamed non-executive chairman.

The departures also have highlighted the continuing rift between former Dean Witter employees – who came with Mr. Purcell to Morgan Stanley in the 1997 merger – and long-time Morgan Stanley workers.

The dissidents – all of whom have roots in the pre-merger Morgan Stanley – said Mr. Purcell has used this division in the ranks to shore up his position as chairman and CEO.

The continuing drama has created concern among the company’s shareholders. On Tuesday, the Council of Institutional Investors, a group of big public and corporate pension funds, asked for meetings with the board of Morgan Stanley and the dissidents so they could ask questions of them.