BioA K9 Clone Trooper (or Massiff Clone Trooper) is a type of Clone Trooper Specialist who were assigned to the Coruscant Elite Guard's patrol units around the Grand Army of the Republic's headquarters on Coruscant.
The K9 Clone Troopers rarely saw action, yet were always on patrol throughout the entire base on Coruscant towards the end of the Clone Wars Era. They primarily apprehended criminals with the other Republic Security Clones (Shock Troopers) and used their canine "dogs" (massiffs) to hunt and/or track down the more secluded or hidden criminals who were practically invisible to the other Clones or even Jedi.
The leader of the K9 patrol unit is known as Sergeant Hound.
They wore modified Phase 2 armor which consisted of having a type of rebuilt AT-RT Driver helmet (similar to the 501st AT-RT Driver's helmets) a kama, and a reinforced com-link antenna on one of their shoulder pads.
Their helmet markings resembled jaws of a beast, and had symbols which represented their position (being k9 Clones). Their markings also had a unique design which was colored in the Coruscant Elite Guard's official color scheme.
Although their helmets resemble Phase 1 ARF Scout Troopers helmets, their actually rebuilt from such helmets fitted with Phase 2 AT-RT Driver gear.
They occassionally used electro staffs similar to what Magna Guard Droids used (aside from Shock Troopers).The actual armor is reskinned from Clone Commander Thorn's armor, as well as the helmet being redesigned after the 501st AT-RT Driver's.
Star Wars: The Clone Wars "The Jedi Who Knew Too Much" (First Appearance)