Sea urchins are echinoderms, in the same family as starfish. Squid do not have external shells, but they are mollusks. 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.