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Exchange-traded funds are expanding their quest to take over the investing world. The $2.1 trillion industry already has set a record in 2015 for fund creation with 2½ months to go. Some 231 new funds have been added as of Wednesday to the increasingly diverse stable of vehicles that look like mutual funds but mostly follow indexes and can be traded like stocks. That total is more than the 202 ETFs created in all of 2014 and represents 38 percent growth from the same period last year, at which time there had been 167 new funds created, according to ETF.com.

The total number of ETFs has grown 7.8 percent in 2015, while assets under management have risen 5 percent, with net inflows of $214.6 billion, according to XTF.com. The growth of ETFs has taken a bite out of the competing mutual fund industry, which generally features actively managed funds with higher fees. Mutual fund assets excluding money market funds stand at $12.9 trillion, down 4.8 percent from a year ago, according to the Investment Company Institute. That decline has come even though the total count of funds is up 2 percent from a year ago to 8,044.

There have been some notable new ETF entrants this year, in particular bond guru Jeff Gundlach's DoubleLine Total Return Tactical fund, which quickly attracted $1.3 billion in assets. That pales in comparison with the industry's leaders, like the SPDR S&P 500, which has nearly $172 billion under management, or even the largest bond fund, the $27 billion , but its growth is remarkable. Read MoreIs this the world's most crowded trade?

But it's also been a year where the trend toward more exotic funds has flourished as well.