Villain(s)  Giant mollusk

Actor(s):  Tim Holt, Audrey Dalton, Mimi Gibson, Hans Conried

Brief Description  The Monster That Challenged the World is a 1957 black-and-white science fiction horror film directed by Arnold Laven and starring Tim Holt and Audrey Dalton. An underground earthquake in California's Salton Sea opens an ancient fissure, unleashing a horde of giant, prehistoric, bloodthirsty sea snails/mollusks that terrorize the local area and threaten to spread.

Plot:
An underwater earthquake at the bottom of the Salton Sea opens a deep crevice. This rupture warms and releases buried, dormant eggs belonging to an unknown prehistoric species. A Navy skydiver testing parachutes lands in the water and vanishes. The two rescue sailors sent to pick him up are also killed. Their patrol boat is discovered floating empty and coated in a mysterious, thick white slime. Rigid but dedicated Naval investigator Lt. Commander John "Twill" Twillinger takes charge of the case. Divers recover the bloated, drained bodies of the victims—which have been entirely sucked dry of their bodily fluids. While searching the sea floor, Navy divers locate and retrieve a massive, translucent egg sac.

They bring it to the base laboratory for study under the supervision of prominent scientist Dr. Rogers. The eggs hatch into massive, caterpillar-like sea snails featuring pincer-jaws and bulging eyes. The monsters escape the landlocked Salton Sea by slipping into the extensive irrigation canal system of California's Imperial Valley, preying on local citizens along the waterways. Dr. Rogers realizes that if the creatures breach the canal locks and enter the Pacific Ocean, they will multiply uncontrollably and threaten the entire planet. Armed with dynamite and firearms, Twillinger and the military race to locate the main nesting ground to destroy the beasts before they escape the valley.