
Poor jobs numbers sent the stock market tumbling on Friday, as nine in 10 sectors finished in the red. Nonfarm payrolls grew by 192,000 in March, a slower rate than the 200,000 expected. The S&P 500 Index (^GSPC 0.83%) lost 23 points, or 1.3%, to end at 1,865. But 1.3% was nothing compared to the declines seen by the three worst stocks in the S&P 500: E*Trade (ETFC), Intuitive Surgical (ISRG 0.74%), and Micron Technology (MU 0.26%).
E*Trade shares shed 7.9% as concerns about "order flow" started popping up. Michael Lewis, the famous financial journalist and author of books like Liar's Poker and Moneyball, is coming out with a new book, Flash Boys, about high-frequency trading. Some of the revelations Lewis made in his 60 Minutes appearance on Sunday are making investors worry that regulators might change the way orders are processed. The concern is for the retail investor, and Lewis alleges that the average retail investor is getting ripped off. E*Trade could feel some financial ramifications from the allegations if regulators decide to change the way orders can be placed.

The arms of the new da Vinci Xi system. Source: Intuitive Surgical website
Shares of Intuitive Surgical, on the other hand, lost 6.5% after a week-long investor lovefest. Even after today's slump, shares of the robotic medical devices company are up more than 16% in the last five days. Intuitive Surgical relies solely on its surgical da Vinci robots for success, and the FDA just approved a new-and-improved version of the machine, the da Vinci Xi. Health care and technology were the two worst-performing sectors in the markets, so Intuitive Surgical was already facing an uphill battle today.
Lastly, shares of semiconductor company Micron Technology lost 5.9% in trading Friday, even after beating both quarterly earnings and revenue estimates. The decline came after the stock was up more than 2% in early morning trading, but plunged along with the rest of the market as the day wore on. The average selling price of its flash memory products was higher than expected, which is very important for Micron as it transitions from PC-based memory products to flash memory, used far more often in mobile devices and corporate data storage.