Blizzard's Left 2 Die custom map, a mashup of Left 4 Dead and their own Outbreak campaign mission, starts out with familiar zerg units (from the campaign, if not from multiplayer) assaulting your base, but even during the first night, you will be attacked by "special infected" (so named in the SC2mapfile).
As a formerly avid Left 4 Dead player, I notice the named similarity between these 4 zerg units and Valve's original special infected.
However, due to the random matchmaking nature of the custom games I tried, I have yet to survive the first night or encounter anything other than the Hunterling (which jumps up cliffs? Maybe something else?).
What are the traits and special abilities of these 4 units? Bonus points if you include pictures of the 4 special infested!