From the main site again:
A starfish living in the sea mutates into a giant monster after heavy exposure to pollution. The creature eventually ends up battling Godzilla.
After Yoshimitsu Banno finished directing Godzilla vs. Hedorah (1971), Banno begun work on creating another installment in the Godzilla series. Like his first Godzilla movie, Banno had wanted the next film to have a strong message against pollution. Banno scraped the idea however and started coming up with a different Godzilla film Godzilla vs. Hedorah 2.
Note, the name Hitodah was not the Kajiu's real name, the creature was unnamed when the idea was scrapped. The name Hitodah originates from the word 'Hitode' which is starfish in Japanese. Also no picture or concept art of Hitodah exists, the above concept was created by the Toho Kingdom and is not the original intent of director Yoshimitsu Banno.