The ShodaiAngira's name comes from shodai (初代?), meaning first generation, and Angira, which comes from Anguirus's Japanese name, Angirasu (アンギラス?).
The ShodaiAngira is thinner and has a slightly bigger nose than the later suits. During filming, the carapace flopped up and down. A notable detail on the carapace is that the spikes are placed in straight rows.
It would seem that this suit's floppy carapace was an intentional feature of Anguirus' design. Subsequent concept art for the unmade film, Godzilla vs. Ghost Godzilla, shows a design for Anguirus with the halves of his carapace being able to move around.
This is the first of Toho's suits to ever be used by another company along with Godzilla. Both ShodaiAngira and GyakushuGoji were to star in an American adaption of Godzilla Raids Again title The Volcano Monsters which had been planned to be released 2 years after the original. Both the suits instead portraying radioactive monsters were to act more like dinosaurs and thus were to be reduced in size comparable to a dinosaur's. However due to bankruptcy the production studio, AB-PT Productions, went out of business the same year of the film's intended release. Godzilla's suit was shipped back to it's rightful owners, but American crew had lost the Anguirus suit and still to this day has been missing ever since. Several years later Toho wanted to feature Anguirus again in Destroy All Monsters, but because of the mishap 13 years ago, this lead Toho to create the more successful and later famous, SoshingekiAngira suit.