Thankfully, I was able to confirm with another site of Segosu's correct name and English spelling, that of Yagosu.
The following guy is so obscure, that I only discovered him on some long defunct (and some still active) tumblrs by chance!
"Daikaiju Yagosu" (or "Yagosu the Giant Monster") appears to be an original manga or story book from the 1960's, featuring a crustacean-type monster. And with a bulging-eyed face that only a mother could love.
And that's all I know about Yagosu, as again, it's that obscure! Of course, if more information comes in, I'll be sure to share it in a follow-up.
However, I will say that The Golden Age of Japanese Monsters, or the 'Kaiju Boom' of the 1960's, went far beyond mere films and television shows.
Resulting in original Kaiju being created for comics, books, magazines, toys, board games, bromide cards, record albums, and advertising. There was even renewed interest for Yokai mythology (Please SEE Shigeru Mizuki), and imported movie and television from America, and elsewhere!
With Yagosu here, being only a small part of this long passed decade of giant monster mania.