Last Week's Biggest Stock Movers Were Riding Big Coattails

General Mills To Buy Organic-Food Maker AnnieÃs For $820 Million
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In any given week, some stocks are sure to shoot up, and others will plummet. The big gainers inspire us to keep investing. The presence of the decliners keeps our greed in check while reminding us about the risks of the equity markets. Let's go over some of last week's best and worst performers.

Annie's (BNNY) -- Up 36 percent last week

The biggest gainer on the New York Stock Exchange was Annie's. The distributor of packaged organic foods soared after General Mills (GIS) struck a deal to acquire Annie's for $46 a share. The $820 million deal will give the cereal giant some more skin in the organic market, which is growing faster than that of traditional grocery items.

On Track Innovations (OTIV) -- Up 31 percent last week

One of the biggest winners of Apple's (AAPL) iPhone 6 announcement was On Track Innovations. A day after Apple showed off its shiny new devices -- and its shiny new Apple Pay system -- On Track introduced an add-on device for older iPhones and iPads that will also help them process Apple Pay transactions too.

On Track's WAVE plugs into the audio jack of older iOS products, giving them the NFC functionality that makes it possible to complete cashless transactions with a wave of your device.

Ulta Beauty (ULTA) -- Up 16 percent last week

Beauty salon operator Ulta Beauty moved higher after posting better-than-expected quarterly results and boosting its outlook. Ulta Beauty runs a chain of 715 stores that offer beauty care products and salon services.

Sales climbed 22 percent, fueled by expansion and a 9.6 percent increase in comparable-store sales. Earnings per share climbed 34 percent to 94 cents a share, well ahead of the 83 cents a share that Wall Street was forecasting. Ulta Beauty is also increasing its guidance given the improving store-level trends and accelerating expansion plans.

21Vianet (VNET) -- Down 29 percent last week

China's 21Vianet was last week's biggest sinker, tumbling after a critical report by Trinity Research Group accused it of bogus accounting. The report accuses the Chinese Internet company of using acquisitions to pad its apparent performance. 21Vianet refuted the claims, but investors are holding out for more clarity.

GT Advanced Technologies (GTAT) -- Down 25 percent last week

On Track Innovations may have been a big winner on Apple's iPhone news, but GT Advanced Technologies went the other way. At least three analysts lowered their price targets on GT after it was revealed that the crystal display provider's products won't have as big a role as expected in the new iPhone 6.

Chatter leading up to the event suggested that GT's sapphire material would be used for the cover screen of the new iPhone. It won't be. There's a strong possibility that sapphire will be the screen material for the Apple Watch when it hits the market in a few months, but that's not expected to be as big a seller as the iPhone.

SeaDrill (SDRL) -- Down 11 percent last week

Offshore drilling contractor SeaDrill suffered a double-digit decline after an unflattering analyst note. Canaccord Genuity initiated coverage with a "sell" rating, fearing that the current climate of low oil prices will see a slowdown in contract activity. This could be problematic if Seadrill has to lower its meaty 11.1 percent yield.

SeaDrill's CFO warned later in the week that as bad as things are now, 2015 could be even worse. Contracted rates for its ultra-deepwater rigs have fallen sharply since peaking last year.

Motley Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool recommends Apple, SeaDrill and Ulta Beauty. The Motley Fool owns shares of Annie's, Apple, and SeaDrill. Try any of our Foolish newsletter services free for 30 days.Check out our free report on where the real money is to be made from the just-announced.