Space Amoeba (1970)
Space Amoeba, released in Japan as Gezora, Ganimes, Kamoebas: Kessen! Nankai no Daikaijū, is a 1970 Japanese Science Fiction/Kaiju film produced and released by Toho Studios. Directed by Ishirō Honda, and featuring special effects by Sadamasa Arikawa, the film starred Kenji Sahara and Yoshio Tsuchiya. The film tells the story of extraterrestrial amoeba-like aliens that highjack a probe and, after crash landing on a small South pacific atoll, create gigantic monsters from native lifeforms (a Kisslip cuttlefish, Rubble crab and Matamata turtle) with plans of conquering the Earth.
More at Wikipedia.