Sea snail eggs

Question: "We found a strange sand spiral in Puerto Rico. I was scuba diving on the coast of Puerto Rico and saw, as it seemed to me, algae or corals covered with sand. I took it ashore and realized that it literally consists of sand, even broke off a piece to make sure. What could have created this formation?"

Answer: "It's a spiral with sea snail eggs."

They consist of grains of sand held together by a gelatinous substance, inside of which there are eggs.