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So I have seen people including them as troops in there lists, I thought it was an HQ what am I looking over in the codex?
That would be "The Scuttling Swarm" on page 91. Under the Termaguant entry. Take a unit of termaguants, you get the option for a troops choice tervigon.
Your friendly neighbourhood gargantuan creature
And under that rule you get a MC that is a troop choice and how awesome is that!!! Just keep them in whatever cover is on the board, and move them up with your other hard hitting cc combat squads to confer FnP on them. You should also run more than one in your army whenever possiable, they do far to much not to have them in there. Dawn of War games become a no brainer to front load 2 Tervigons and your Hive Tyrants.