Next Question 15. Barnacles and sea urchins are not mollusks. Barnacles are arthropods, a family of species that include insects and crustaceans. 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.