Nasdaq OMX hit with 4th recent executive departure

* Adam Nunes, head of U.S. options, to leave this week

* Concannon, Mulholland left in last two months

* CFO Warren to step down in July, leave firm in December

NEW YORK, May 18 (Reuters) - Exchange operator Nasdaq OMX Group Inc (NDAQ.O: Quote, Profile, Research) confirmed on Monday that its head of options, Adam Nunes, would leave the firm later this week, the fourth departure to come to light in the last few months.

Company spokeswoman Silvia Davi did not say why had Nunes decided to leave, or where he was going. His last day is Friday, she said.

Since April, the operator of the Nasdaq Stock Market has lost Chris Concannon, its head of transaction services, and technology senior vice president Darren Mulholland. Both went to high-frequency trading firms.

Chief Executive Robert Greifeld announced in February that his chief financial officer, David Warren, would step down in July and depart at the end of the year, to be replaced by Adena Friedman, the executive vice president of corporate strategy and global products.

Concannon and Warren were particularly central in integrating Nasdaq's myriad acquisitions over the last few years, including Nordic exchange group OMX and the Philadelphia Stock Exchange, which is one of Nasdaq OMX's two U.S. options markets.

"They have a lot of integration expertise that's leaving here, and a lot of cost-cutting expertise," said Patrick O'Shaughnessy, analyst at Raymond James and Associates. "If that is central to your thesis as to why Nasdaq is a compelling investment, I think that is perhaps some cause for concern."