WebMD

(HLTH)

said Jeffrey Arnold resigned from his post as co-chief executive, as well as director of the company, leaving Martin Wygod as the lone CEO.

Jim Clark also resigned from the board. Clark founded WebMD's predecessor,

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Healtheon

, in 1996 with Pavan Nigam, who resigned from the post of chief technology officer earlier this month.

Shares of WebMD, an Internet-based health-care company, were recently trading up 25 cents, or 2.6%, to $9.88.