Infested Iiig are Iiig infested with a Xrondo parasite. They are most often seen being hosted by a Type 3.
Sporepedia Description[]
"When the Crux invade locations, sometimes their luck runs out and they encounter horrors such as the Xrondo. In the case of the Iiig, their sensory tentacles make excellent bases for the legs of the Xrondo, and the emergence is perfect from these spots."