UPDATE 2-NYSE Euronext quarterly revenue falls a fifth

* NYSE net quarterly revenue off 21 pct to $559 mln

* Group Q3 net income down 42 pct to $108 mln

* NYSE Euronext earnings per share at $0.44

LONDON, Nov 6 (Reuters) - NYSE Euronext, the world's largest stock exchange operator, reported net revenue down 21 percent to $559 million for the third quarter, citing weaker trading in the United States and Europe.

The group said on Tuesday net income for the three months to the end of September was down 42 percent to $108 million, while earnings per share were off 38 percent at $0.44.

The results reflect weaker trading activity in the group's main equities and futures markets in New York, London and Paris because of ongoing concerns about the global economy and a strong third quarter last year.

NYSE said on Tuesday net third quarter revenue in its futures and options trading unit was down 27 percent to $164 million as share trading activity dropped 20 percent to $282 million.

``Market volatility since the third quarter of 2011 has significantly declined, reaching multi-year lows in August of 2012,'' NYSE Euronext said in an emailed statement.

Deutsche Boerse, the exchange with which NYSE tried and failed to merge earlier this year, was last week forced to cut its 2012 revenue target as lower market volatility caused a dip in third-quarter trading.

NYSE and the German exchange were forced to drop their $7.4 billion merger in February this year after European competition authorities blocked the deal amid concerns the transaction would create a monopoly in European futures trading.

The London Stock Exchange and interdealer broker ICAP are set to report their third quarter results next week while British broker Tullett Prebon is up on Friday this week.