Trivia

This was the first giant monster film produced after the death of Toho's special effects director, Eiji Tsuburaya, who passed away in January 1970. The effects were directed by Sadamasa Arikawa who, having been promoted to Director of Special Technique, had already handled most of the special effects since Ebirah, Horror of the Deep (1966) with Teriyoshi Nakano as his chief assistant. Both Arikawa and director Ishirô Honda wanted to include a dedication to Tsuburaya in the film but Toho refused. Arikawa was so disgusted by this that he vowed to never work for Toho again. Director Honda likewise decided to retire from filmmaking due to his disappointment with the direction Toho took their special effects films and the dissatisfaction of working for them.

This was the last Toho production to be made under the old studio system with the actors being under contract to the studio.

All three monsters, the squid Gezora, the crab Ganimes and the turtle Kamoebas have remained relatively obscure and never had a major role in later monster movies made by Toho. However, Gezora gained some notoriety for its appearance as the first boss in Nintendo's Godzilla: Monster of Monsters video game and its brief cameo in Godzilla: Final Wars (2004), and Kamoebas also had a cameo as a carcass washed ashore in Godzilla: Tokyo S.O.S. (2003).

The giant turtle is known in Japan as Kameba and internationally as Kamoebas. The name is a mixture of kame, the Japanese word for turtle, and amoebas.

The story was originally going to take place in Guam. However, this was changed to Hachigo Island because the budget wasn't substantial enough to afford shooting on location in Guam.