The Monster That Challenged the World (1957) on Netflix

An earthquake unleashes a giant mollusk in California's Salton Sea. The site is near a military base and the first victim is a navy skydiver testing parachutes and the two sailors sent to collect him from the water. Soon Naval Investigator Lt. Commander John "Twill" Twillinger is on the case. They find the sailors' boat which is covered with a white goo. Soon Navy divers are looking for the missing men and recover a large round sac which they recover and sent the base lab. One of the divers is killed in an encounter with the creature and they think the crisis is over. They don't realize that the sac they transported to the lab is in fact the creature's egg and another mollusk hatches, this time on the base.