The Angry Red Planet (1960)

Our first manned flight to Mars returns after being thought lost in space. Only two survivors (Mohr & Hayden) of the original four are on board. Mohr has a green growth on his arm, and nothing that the doctors do will kill it. Hayden, under hypnosis, tells of their adventures on Mars. Thought to be a dead planet, it's inhabited with man-eating plants, giant Bat-Rat-Spider-Crab monsters, a strange city on a lake, and a one-eyed monster that dissolves anything that it swallows or touches.