Well there is Mr Krabs, Mrs. krabs, Mr. Krabs grandpa, Larry the Lobster, snelly, the other snail racers, the snails in the pet contest episode.... So on and so forth. It's a saturated environment really, the poor guy had no shot.

GAAAAAARYYYYYY

Is gary the snail truly worthy of your caps lock? If we dig deep down we can also define "shell" as protective casing around an organism which helps it survive. By this definition, Karen (Planktons cyber waifu) could also be considered a shelled creature. This is owing to her hard cold computer casing of course, or in other terms, her shell. One could argue that if you weighed the two against each other, Karen, who has to deal with plankton's bullshit is far more worthy of your caps lock than the mostly freeloading Gary the Snail (who has shown time and time again that he is not entirely loyal to spongebob despite the effort the sponge puts in).

........ Gold star 4 u