Quite a few concepts for monsters were made for Godzilla: The Series but were never used. They were given names used by actual Toho Company Ltd. monsters since they were just quick sketches or ideas. The first picture shows the unused monsters that were cataloged as Anguirus, Biollante, Gabara and the organic and mechanical versions of Moguera. The second pic shows the Flying Gigan, two pics of Gus the Spider, two pics of Manda the Worm, and two pics of Megalon.
Named after the great Ankylosaur monster, this monster would probably have been a burrower but it is unknown as he was never shown outside of one piece of concept art. It has three horns on its head, four on its neck and five on its chin.
Named after the bio-engineered plant monster, this monster had tentacle/vine like appendages and a small head crest but that is all that can be made out. It appeared on one page of concept art.
A homage to the alien cyborg monster, the Flying Gigan is a bat like creature. It is featured in the opening sequence of the show and does battle with Zilla for most of it. It was also featured on a piece of promotional art for the series, battling Zilla in and underwater environment.
Named after the imaginary monster, this monster has very little discernible features aside from its' double-mouth and eight eyes. It appeared on one page of concept art.
Gus the Spider
An homage to the great spider monster, Gus appeared at the end of the opening sequence. The Giant Mutant Widow Spider was based off of Gus' design. Its most notable feature was its extremely large mandibles.
Manda the Worm
An homage to the dragon goddess monster, Manda appeared at the end of the opening sequence.
An homage to the beetle god monster, Megalon appeared at the end of the opening sequence. This creature has large horns, spider-like mandibles and an armored back. It also has very skinny arms compared to its bulky body and tentacle-like hands.
Named after the dividing robot, this monster apparently was supposed to fight Zilla, be K.O.'ed and then be ressurected using robotics. It appeared on one sheet of concept art.
Bird of Prey
This creature (not shown) was originally meant to be in the episode "Wedding Bells Blew". However, due to the amount of bird-like monsters in the series, the Bird of Prey was replaced with the Mutant Manta Ray.
This creature (not shown) was originally meant to be in the episode "End of the Line". However, the show's producers didn't want another Godzilla in the series. Therefore, the Female Godzilla was replaced with the mutant komodo dragon, Komodithrax.