The Securities and Exchange Commission delivered a win to the $2 trillion exchange-traded-fund industry Thursday night, approving a new type of fund structure that doesn't have to disclose its holdings.

In a filing, the SEC said Boston-based Eaton Vance can launch a so-called nontransparent ETF that will trade on an exchange but doesn't have to disclose its holdings and doesn't follow an index like a typical fund. Eaton Vance has plans to launch 18 such funds over the coming months, the first fund company to do so, according to the company.