CVS Caremark Corp., the parent company of CVS/pharmacy, says Larry J. Merlo, who oversees the company’s retail operations, will succeed Thomas M. Ryan as chairman, president and CEO when Ryan retires in May 2011.

CVS, No. 73 in the Internet Retailer Top 500 Guide, has named Merlo as president and chief operating office in advance of the succession. Merlo will also serve on the company’s board of directors.

Merlo’s previous title was executive vice president of the company and president of CVS/pharmacy. CVS has not appointed anyone to replace Merlo, who continues to oversee retail operations.

Ryan has worked at CVS for 36 years, including 16 years as president.

“The plan we are announcing will provide for a smooth, seamless transition in the leadership of CVS Caremark,” he says.

CVS/pharmacy in January launched an e-commerce site for its eight Beauty 360 retail locations, which sell cosmetic, hair care, fragrance and grooming products. Last October, the company launched a mobile commerce site, m.CVS.com.