A needle wheel skimmer has a pump with a modified impeller that has little sticks on it to beat the air entering the skimmer from the venturi and the water from the pump into very fine bubbles.
http://www.championlighting.com/pics...0_impeller.jpg

Also, in response to rcombs, I was told the same thing when I entered the hobby, but after buying a skimmer I can confidentally say no reefer should be without one. I have seen very noticable changes in water quality and improved overal health of my system.

Miz:
You have a 34 Solana correct? This skimmer will fit in the rear chamber and does a good job (based on many reviews) of removing skimate.
Hydor Koralia Nano/Slim-Skim Internal Protein Skimmer
review
Hydor’s Slim Skim Nano is about as stealth as an internal skimmer can be
and a video
Hydor’s Slim Skim Nano performer protein skimmer action video