Kamoebas' name is derived from the Japanese word "kame," which means turtle.
Kamoebas' scientific name "Megalo matamata" is derived from the Greek word "Megalos", which means "giant" or "great", the word "mata" is either Japanese or Spanish, but given the fact the matamata turtle is native in Brazil, it suggests that the name is derived from the Spanish word which means "kills" while in Japanese it means "again" or "once more". If the Spanish word was used, then the name would literally mean the "giant kill kill turtle", while if using the Japanese word literally means the "giant once more turtle".
After Ganimes was destroyed, Yog turned to a rock turtle and made Kamoebas. It also made another Ganimes. However, bats fled from a nearby cave and caused Yog to lose control of the monsters. They battled each other up the mountain in the center of the island and both fell into the volcano, destroying themselves and Yog forever.
Kamoebas made a brief appearance in Godzilla: Tokyo S.O.S.. In the film, news agencies and the J.S.D.F. swarmed to a small part of the coast of Japan. A dead Megalo matamata, or Kamoebas, had washed ashore in the night. As it was investigated they noticed several large claw marks on its neck. It becomes clear to the humans that Kamoebas had been killed by Godzilla.
In the movie Godzilla: Tokyo S.O.S., Anguirus was supposed to be the monster whose carcass washes ashore, not Kamoebas. However, staff thought that putting Anguirus in that role would draw negative fan reactions, so they changed the monster to Kamoebas. Another, unconfirmed reason may be because Anguirus is traditionally Godzilla's ally.
Concept art shows that Kamoebas' role also originally was meant for a giant mosasaur, but Toho felt it would be odd to introduce a brand new creature just to have it die in an unseen fight.