Space Amoeba (1970)

“An alien aiming for the Earth transforms monsters to attack!”

When a space probe crash-lands on a far-flung Pacific atoll, the craft's alien stowaways decide to take over their new world one creature at a time. Soon, the parasitic life forms latch onto three indigenous critters -- a squid, a crab and a snapping turtle -- and transform them into colossal mutant monsters.