There are a total of 69 different shells in Another Crab's Treasure. If you want to collect them all, you'll basically need the entire game to collect them all.
Another Crab Treasure | How to Find a Knight's Helmet | Shellslike Achievement/Trophy Guide
If you still don't know where to find all 69 shells, I've included maps below of every location you can find that specific shell. Many of these, like the Soda Can, have multiple locations, so there are other places you can find them. Others are dropped by specific bosses or may need to be purchased from the shell store around town.
This is your shell, the whole point of this adventure. You have it at the beginning of the game, and then you lose it to a loan shark. You get your Home shell back by completing the game.
In Another Crab's Treasure, there are soda cans everywhere, but the first place you can find them is in Nephro's arena, all over the ground and in the vending machine.
