Archipelago Holdings, L.L.C. is the parent company of several securities-related businesses. Following is a brief description of each business.
 

Archipelago Trading Services, Inc.
Archipelago Trading Services is a broker/dealer that sponsors access to Arca Edgesm — our platform for trading small-cap equity securities typically quoted on the OTCBB

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Archipelago Exchange® (ArcaEx®)
The Archipelago Exchange (ArcaEx) is the world’s first totally open, all electronic stock market. Through ArcaEx, our clients can trade more than 8,000 equity securities, including NYSE, NASDAQ, AMEX and PCX-listed securities, ETFs and other exchange-listed securities. For more information about listing or trading on ArcaEx, simply click on the appropriate link.

When you click on the link "ARCA" on http://www.otcbb.com/asp/Info_Center.asp 

(level 2 quote page)

you get the following: 

Archipelago Trading Services, Inc.

NASDAQ TRADING
312-960-1318

OTCBB TRADING
312-442-7700

The name of this company matches the first subsidiary I listed above, not the echange subsidiary which is ArcaEX.

http://www.archipelago.com/inside/subsidiaries.asp

Sounds to me like ARCA is the broker / dealer (maket maker) subsidiary for OTCBB securites.

I'm very specific in company division / subsidiary name.

Maybe too much so.

But I still think that ARCA is the market maker (broker / dealer) for the parent group, which also owns teh exchange you reference.