Some species have internal shells. Trumpet shells are a kind of snail. Next Question 14. Sunlight can fade a shell's color, whether on the beach or in a collector's cabinet. Abrasion from sand and wave action can also fade and wear shells.
Mineral oil is one way to hightlight a shell's color without seriously damaging the shell.
Next Question 13. Giant tridacna clams do not poison people, or anything else for that matter. They eat algae. Some cones have a harpoon that can give a lethal injection. They have killed people.