A remora is a fish that sticks to the side of a shark. The little hitchhiker gains protection and sustenance from its host.

Zynga Inc (Nasdaq: ZNGA) has been that remora, depending far more on Menlo Park, Calif.-based Facebook Inc (Nasdaq: FB) than Facebook has been dependent on it.

The San Francisco-based software developer saw its share price tumble more than 40 percent after its quarterly earnings released after markets closed Wednesday revealed that it not only missed its sales target, it didn't even come close: sales of $302 million for the quarter instead of the projected $344 it was supposed to make. It lost $22.8 million and steeply dropped its forecast for the year.

The development has some shareholders fuming and on Thursday the law firm Newman Ferrara LLP said it was initiating an investigation to see if company officials unloaded 43 million shares of the company's stock in early April when a share was valued at $12, earning over $500 million.

"These insider sales were executed during the second quarter of 2012 shortly before Zynga reported terrible financial results for that quarter," said a statement from the firm.

The company filed an IPO in December with a starting share price of $9.50. On March 2 the price peaked at over $14 before it started declining. The price closed Wednesday at $5.07 prior to the annoucment of the earnings.

Zynga went public on the back of the popularity of so-called "management style" or "freemium" online games, which are built around players' willingness to build virtual farms (FarmVille), virtual cities (CityVille), virtual fiefdoms (CastleVille) and other virtual non-Ville related games.

These games, which are still immensely popular, are free to play. The catch is that they're not nearly as fun unless players whip out credit cards buy imaginary things; if your virtual plantation needs a virtual tractor, you buy one; with real money.

In 2009, FarmVille users peaked at 80 million, and the company became the No. 1 app developer on Facebook. The company relies very heavily on users' ability to easily discover its games on Facebook. It also heavily depends on FarmVille, which represents 29 percent of its revenue, according to Reuters.

For its part, Facebook reportedly relies on 15 percent of its revenue on Zynga. Shares in the social networking giant took a dive Thursday on the back of Zynga's disappointing earnings report. Now, all eyes will be on Facebook's first earnings report due Thursday's after markets close.

Facebook recently tweaked its search algorithm on the way online games are discovered. Now they are presented by the most recent offerings rather than the most popular, which has buried FarmVille in the rankings and was a key reasons for the stock's decline

"The biggest factor impacting current performance appears to be the way Facebook is surfacing gaming content on its platform," Doug Anmuth, J.P. Morgan analyst, told the Wall Street Journal.

What this means is Zynga's moneymaker will be harder for new users to discover, and its newer offerings haven't been nearly as popular. Meanwhile,. Facebook appears to be consciously evolving its strategy, which means the remora might have a harder time riding on the back of its host.  

Shares fell $1.99, or 39.15 percent, to $3.09.