A Long Beach, Calif.-based casual gaming company founded way back in 2004, called GoPets, has sold to social gaming giant Zynga for an undisclosed sum, according to a Facebook status update from a GoPets founder spotted by Virtual Goods News over the weekend. Zynga is not commenting on the acquisition.

Why would Zynga want this company? Right off the bat, it’s easy to think that Zynga is looking more seriously at virtual pet-caring games, along the lines of SGN’s (fluff)friends or Playfish’s Pet Society. From the GoPets company description:

GoPets is an online world that revolves around 3D virtual pets. You can adopt a cat or dog, and design it’s very own 3D virtual land on which it lives. A GoPet can be dressed up in fancy clothing, eat exotic foods, and interact with the different items that you buy it.

But it’s not just the game genre that has similarities to Zynga. GoPets also includes a very evolved set of virtual goods monetization features. There’s a mini-game section, a multi-currency virtual economy, a premium subscription service, and a lot more — the game is popular enough to warrant this Wikipedia entry that will tell you about it in detail. GoPets also has what appears to be a couple of spin-off sites, including GoDance and Big Bad Puzzle.

Zynga, of course, has increasingly complex virtual economies running in its own games. One acquisition, of MyMiniLife earlier this year, came with technology that was quickly put to use in its hit game FarmVille. What’s more, Zynga appears to be getting into the popular social game genre of fish-themed games — it got a trademark for “FishVille” recently, for example.

Also, from what we can tell, GoPets has deep roots in Asia: Wikipedia and VGN wrote that it is based in Seoul, South Korea (the company web site lists its location as Long Beach), and it also won a Red Herring Top 100 Asia startup award in 2006.  On a related note, we heard awhile back that Zynga has been visiting Asia more often; in fact, we got a tip that something big was happening with GoPets, a number of weeks ago. As Zynga is not commenting, we’re assuming that GoPets was one of the fruits of Zynga’s exploration. Now, according to VGN, at least some of the 55-person company will be working out of Zynga’s much larger San Francisco headquarters.