Aliens 1 was to be an IG Aliens supplement, their earlier Aliens Archive having been pretty roundly condemned. Again each of the CORE team took a different piece - I landed the Graytch which had been briefly covered in Aliens Archive but were felt to warrant a fuller treatment. The Graytch were a bunch or arboreal (tree dwelling) six legged spider/centaur crossed. There's a beast in Spy Kids 2 ( the spider-monkey?) that's pretty close to my current mental image of them. The neatest thing about them was that they were pacifist.
Aliens 1 was pulled by IG after it had all been written and as they started to pull out of Traveller. We never got paid for Aliens 1.
My abiding memory of Aliens 1 was writing a chunk of it on a Psion 3 in business class on a Cathay Pacific 747 between Hong Kong and London on the way back from a business trip to New Zealand. The life of a Traveller writer eh?