The Fat Butterfly has just been swallowed.

Business-to-business software maker

Commerce One

(CMRC)

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Tuesday said it would acquire

Exterprise

, a privately held software company that focuses on the collaboration market, for $70 million in stock.

The move comes seven weeks after archrival

Ariba

(ARBA)

said it would buy

Agile Software

(AGIL)

, which makes collaboration software, for $2.55 billion in stock. The value of that deal, however, has sunk to less than $720 million as Ariba's stock has plummeted in the stock market selloff.

This deal is sure to become smaller, too. Commerce One's press release, put out after the close of markets Tuesday, valued the deal at $78 million based on Monday's closing price for Commerce One shares. By Tuesday's close, though, after Commerce One's shares dropped $1.04 to $9.38, 10% of the deal's value had vanished.

The deal is part of a wave of consolidation in the software sector and comes on the heels of

i2 Technologies'

(ITWO)

planned acquisition of

RightWorks

, as well as

FreeMarkets'

(FMKT)

planned acquisition of

Adexa

.

Because B2B networks are made up of pools of buyers on one side and sellers on the other, connected in the middle by an online exchange, they're often described as having a "fat butterfly" business model. Exterprise likes to boast that it's "the power behind the fat butterfly."

In a statement, Commerce One CEO Mark Hoffman said Exterprise will give Commerce One a leg up in the hot market of "collaborative commerce."

"Our customers tell us that collaborative e-marketplace applications designed for specific companies, industries or regions will drive the next wave of e-marketplace adoption," Hoffman said. "We believe this acquisition will give us the ability to extend our leadership of the e-marketplace category."