Synopsis by Hal Erickson

The Monster That Challenged the World is the misleadingly title for one of the more well-regarded second-echelon horror films of the 1950s. An underwater earthquake in the Sargasso sea yields up the eggs of a long-extinct sea monster. Once hatched, the monster's offspring (which resemble huge snails) sustain themselves by sucking the life forces of various unlucky human land dwellers. Even worse, these horrendous creatures procreate at an incredible rate, laying 3000 eggs per sitting. Eventually, the monsters are neutralized by Modern Science, save for one stray snail that very nearly lunches on a little girl..

http://www.allmovie.com/movie/the-monster-that-challenged-the-world-v33176