Thank you!
That is a very good question, and one I've been asked before. I'll give the backstory of the Dragon Snail species here, which will explain the too-small-to-hide-in shells:
Quote:
Dragon Snails: the story of the species
The species Draco domiporta™, common name Dragon Snail™, first appeared in 2003. Little is known about this elusive species, as they tend to evade capture when biologists are involved, though they are tolerant and even affectionate to people with benign intent. Scientists are baffled by the apparent intelligence and parapsychic abilities of these creatures; most of the information gathered about them comes from laypeople.
It is not surprising, then, that the species name "domiporta" is something of a misnomer. Literally "one with her house on her back" or "snail," Dragon Snails™ do not have the ability to retreat inside their shells as snails do. Rather, the shell appears to be an affectation adopted by the species as a way to attract food. Mostly carnivorous, the species seems to prefer a diet of snails. They will also eat some funguses and algae, as well as insects, frogs, birds, and small rodents whose intention was to make a meal of them. Larger would-be predators are strongly discouraged by a fierce nip or a sharp horn. Dragon Snails™ are far faster than they appear and may even snatch a swooping bird out of midair!
(c) 2005-2009 Erin "Eirewolf" Metcalf
Dragon snails can change their shell at will, as you or I would change a shirt (though they don't do it quite so often). Of course they have to do this as they grow (or else they look ridiculous with an even more proportionately tiny shell on a large body), and sometimes they do it because they've found a new shell they like better.