Unfortunately, that's exactly what happens when the rescue party (Lars, Zeetha, Dimo, Ognian, Maxim, Sturvin and Kalikoff) opens one door too many while trying to extract themselves from the Deepdown and get back to rescuing Agatha.Before they can retreat, Dimo gets stung on the arm by one of the GGTs, and his arm begins to turn into green goo. Oggie deals with this in typically Jägerish fashion: he simply Dimo's arm, reasoning that as soon as they find a Heterodyne, he (or more accurately "she," as they've figured out who Agatha is by now) can make him a new one. Dimo is perfectly happy with this analysis and carries on just fine with one arm, but it's this exchange that convinces Zeetha that her Zumil is the heir to House Heterodyne. Meanwhile, the severed arm deliquesces into green goo and is lost from the story, which is just as well.
They're probably seen once again later. As Sun Jen-djieh is regaling Gil with tales of Klaus's rescue by The Unstoppable Higgs, helpfully providing us with a flashback sequence in the process, something green-glowy-thingish is infesting the medical airship. (Dr. Sun thinks they're some kind of biological weapon, which fits.) Somehow Higgs manages to deal with them and carry on. Dr. Sun notes that the ground troops got some "samples" of the critters, so they may have been part of the Battle of Sturmhalten as well, although it's other monsters that are actually seen there.