While they exactly look that way, when looking at Alien Pegassa’s costume, his lower part of the body appears to have been made of a fabric material instead of latex.
I had long thought they applied the material to the costume to reduce cost, I have just come up with another idea right after my post about the making of Alien Pegassa.
The thing is, there is a speculative explanation that Tohl Narita might have designed some of his aliens so that they were dressed with spacesuits.
Narita says in his art book that Alien Mefilas of “Ultraman” was a design he worked out when he started working on design development of “aliens” instead of kaijus and kaijins (mysterious human) in earnest.
And there is speculation that Alien Mefilas was designed as an alien wearing a spacesuit, and, come to think of it, that might be the way he looks.
This speculation might make it more plausible that Ultraseven aliens were designed on the assumption that they were dressed with space suits although the suit appears to have been integrated into the whole body of the alien.
It is true that we find many aliens who are actually dressed like Alien Shaplay or Alien Shadow in “Ultraseven” although they got dressed for cost cutting while it saved time and money to sculpt their bodies.
If the speculation should be true, Alien Pegassa’s fabric-looking lower body might have been meant to be his space suit along with his fisherman sweater.
It is only natural that kaijus are undressed, certainly, but aliens could be in their space suits.
Now that Narita is not alive, I don’t think there is any way to make it sure without him whether he designed the aliens with their space suits in mind.
Incidentally, Alien Pumpkin was a dressed alien with a cape while it is unknown who designed and sculpted the character…sorry for my irrelevance!