NEW YORK (

TheStreet

) --

IntercontinentalExchange

(ICE) - Get Intercontinental Exchange, Inc. (ICE) Report

's announcement Thursday that it would acquire

NYSE Group

(NYX)

sparked strong moves in the three other public-traded US exchanges, though the scenario implied by those moves invites a great deal of skepticism.

Shares of

Nasdaq OMX Group

I:IXIC

rose 3.53% to close at $26.11, while shares of

CBOE Holdings

(CBOE) - Get Cboe Global Markets Inc Report

gained 3.96% to $30.68.

Are investors betting they'll be acquired? Who do they think will do the acquiring? Richard Repetto, analyst at Sandler O'Neill, was left shaking his head.

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"No one knows. Some other exchange from overseas. I don't know. Maybe Nasdaq tries to buy CBOE. It's just these merger arb guys that just don't know the space very well and the whole space goes up on stuff like this," he said.

Even if Nasdaq and CBOE do get acquired, it isn't at all clear they should be worth more than they were as of Wednesday's close. Deals take many forms, and market responses are difficult to predict.

That unpredictability was clearly in evidence Thursday. NYSE shares opened 38% higher at $33.27, slightly above the agreed-upon price of $33.12 per share, before drifting slightly lower throughout the day to close at $32.25. Shares of ICE, meanwhile, opened 5.5% higher but quickly dropped, spending much of the morning and early afternoon in negative territory. They recovered in the final two and a half hours of trading to close at $130.10, a gain of 1.40%.

CME Group

(CME) - Get CME Group Inc. Class A Report

, meanwhile, started out higher, but spent most of the day below where they closed on Wednesday. Shares closed Thursday down 2.34% to $51.40.

The market's apparent conclusion is that CME faces a much stronger threat from a combined NYSE and ICE.

But analysts appeared to express a healthy amount of skepticism about Thursday's deal.

Barclays Capital's Roger Freeman, for example, wondered where the planned cost savings would come from.

"Can you just talk a little bit more about where all these additional opportunities are? ICE, your margins are already at very high levels. Does this imply that Project 14 (an NYSE cost-cutting plan) missed a lot of additional opportunities?" Freeman asked on the conference call following the deal's announcement.

If the deal proves to be a mistake, in other words, that would presumably allow CME to gain ground on a troubled competitor.

Taking a look at the exchange stocks on Friday, it would be tempting to buy everything that was sold on Thursday and sell or short everything the market bid up. At the very least, it looks like Thursday's announcement settled very little.

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Written by Dan Freed in New York

.

Follow @dan_freed

Disclosure: TheStreet's editorial policy prohibits staff editors, reporters and analysts from holding positions in any individual stocks.