I remember seeing something years ago that said that if you press SHFT of ALT or some other combination during the equip screen of a Sectoid mission, the Sectoids would appear to be a different race of aliens. If I remember right, they were a canned species that didn't make the final cut. I seem to remember them as being floaty, tenticly ugs. Maybe something like a Tentaculat? I looked on the wiki and elsewhere but can't find any mention of this. Is this a myth, fact or product of my imagination?

It's part myth, part true. They do not exist in-game so there's no way to get them, but they did appear on the box art on some releases of the game - the European release if I'm not mistaken. I guess it's simply following in the fine tradition of putting box art that has nothing to do with the game (or looks nothing like the game at all) on overseas releases.

- NKF

Are we talking about this one? (top images):

http://www.mobygames.com/game/x-com-ufo-defense/cover-art

I haven't heard of this particular "Easter Egg" before, but I doubt anything like this is included since the programmers didn't add any Easter Eggs or cheats for any of the games up till interceptor.

- Zombie

UFO has no hidden alien art, but TFTD has a little.

Mobygame's doesn't appear to like the direct linking, so you could try their listing of the various covers. Looks like it was more common than I thought.

http://www.mobygames.com/game/x-com-ufo-defense/cover-art

- NKF

Yeah, that was the bugger! Thanks for the replies, guys. It probably was just a myth, but I'm going to press some buttons during equip screens just in case Although I suspect you guys have gone through all the files for editing and modding already...