The Monster That Challenged the World 1957

In the Salton Sea in California, an underwater earthquake opens a crevice and releases prehistoric giant molluscs. A rescue training parachute jump is staged, but the patrol boat sent to retrieve the jumper finds only a floating parachute. One sailor dives in and disappears, while the other screams in terror as something rises from the depths.

When the patrol boat does not answer radio calls, Lt. Cmdr. John ‘Twill’ Twillinger leads a second rescue party aboard a patrol boat to investigate. They discover the deserted craft coated in a strange slime; the jumper’s body surfaces, now blackened and drained of bodily fluids. Twill takes a sample of the slime to the base lab for analysis, where he teams up with recently widowed Gail MacKenzie and Dr. Jess Rogers.

A young couple disappears after swimming. U.S. Navy divers investigate and uncover a giant egg and the body of one of the victims on the ocean floor. The divers are attacked by a giant mollusc (resembling a giant caterpillar), which kills one diver. The mollusc attacks the boat, but Twill stabs it in the eye with a grappling hook. The egg is transported to the Navy lab for study and kept under temperature control to prevent it from hatching.

The molluscs escape into an irrigation canal system, threatening livestock, a lock keeper, a trysting couple, and others. Navy divers locate a cluster of molluscs in the canal system and destroy them with explosives.

Meanwhile, Gail is at the lab with her young daughter, Sandy MacKenzie. Worried about the rabbits kept in the lab getting cold in the lowered temperature, Sandy surreptitiously turns up the thermostat. Twill calls the laboratory and finds no answer. He arrives to discover that the hatched mollusc has Gail and Sandy cornered in a closet, where they had fled to escape the creature. He fights it with laboratory chemicals, a CO2 fire extinguisher, and a live steam line until other Navy personnel arrive and shoot the mollusc.