This is a picture of my regulator. This chrome section at the top right is the first stage, which attaches to the air tank. The primary second stage, which includes the mouthpiece, is the black component in the middle of the picture. Those two components together are a set, the AquaLung® Legend.
The yellow spare second stage, at the lower left, is an AquaLung model specifically intended as an emergency back-up.
The two air hoses leading off the bottom of the image go to the dive computer and the buoyancy compensator (vest).