Sun Microsystems Inc. (SUNW) said on Wednesday that President and Chief Operating Officer Ed Zander is leaving, the latest in an exodus of senior executives at the maker of computers that manage corporate computer networks. 

Effective July 1, Chairman and Chief Executive Scott McNealy will take over Zander's duties, reassuming the additional title of president. The company said it does not intend to name a replacement for Zander, who will stay on through year end to help in the transition. 

Zander, who runs Sun's day-to-day operations, is the third senior Sun executive to leave in the last few weeks, and his departure is the one analysts have feared most since Chief Executive Scott McNealy said recently that he had no plan to retire. 

Sun's stock traded lower in pre-market trade at $7.30 on Instinet, down from the close of $8.18. 

"Over the last 15 years, Ed has worked tirelessly to lead Sun through several transformations and to the forefront of the computer industry," McNealy said in a statement.