Posterous may have lost the online popularity contest to Tumblr, but the social blog service has won a worthy consolation prize: It has been acquired by Twitter, an even more popular micro-blogging service.

Sachin Agarwal, founder and CEO of Posterous, announced the deal in a post on Monday.

"The opportunities in front of Twitter are exciting, and we couldn’t be happier about bringing our team’s expertise to a product that reaches hundreds of millions of users around the globe," he said. "Plus, the people at Twitter are genuinely nice folks who share our vision for making sharing simpler."

The price of the deal was not disclosed.

Launched in May, 2008, as a Y-Combinator-funded start-up, Posterous received early attention for its post-via-email capability and ease of use. Though widely used, it has grown slowly while rival Tumblr, started about a year earlier, has seen its popularity soar.

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Twitter's post about the deal suggests Posterous has been "acquhired," which is to say bought more for its software engineers than for anything else.

"We're always looking for talented people who have the passion and personality to join Twitter," the company said in its blog post. "Acquisitions have given us people and technology that have enabled us to more quickly build a better Twitter for you."

As to whether a better Posterous will follow from the deal, that appears doubtful. The start-up ducks its own question, "Will Posterous eventually shut down?" Rather than answering with a reassuring and unambiguous "No," Posterous explains that users can continue to access their Posterous Spaces as they have in the past. The company then leavens that non-answer with a measure of doubt: "We'll give you ample notice before any changes or disruptions to the service and we'll provide specific instructions for exporting your content to another service."

Developer Marco Arment, who built Tumblr before leaving to work on Instapaper, suggested Posterous will shut down within six months.

"Now I have a better answer than 'LOL' for that (one) guy who asked me to add send-to-Posterous support to Instapaper a few months ago," he quipped in a Twitter post.

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