Cue the pictures of anguished traders: The Dow closed down 376.36 points, or 3.6 percent, on Thursday, driven largely by fears about Europe’s debt. The matter wasn’t helped by an unexpected rise in American jobless claims, which jumped 25,000 to 471,000 for the week ending May 15. The S&P 500 is also down 10 percent from its 2010 high, and all of its 2010 gains have been erased.