From the Super Mario Wiki
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Super Mario series
Super Mario 64/Super Mario 64 DS
They first debuted in Super Mario 64 and its Nintendo DS remake Super Mario 64 DS, appearing in Jolly Roger Bay and Dire Dire Docks. They are known as "Clams" in these two games. Most Clams in Jolly Roger Bay contain Red Coins, whilst the lone Clam in Dire Dire Docks contains a Koopa Shell. If a Clam is touched whilst it is opening or closing, Mario takes two points of damage. Clams open up for a small period of time when Mario approaches them.
New Super Mario Bros. Wii
Clampies reappear in New Super Mario Bros. Wii, only appearing in World 1-4 and in a secret area in World 4-1. They trap a character in its shell if it closes on a character, causing them to take damage and then opening back up. Most Clampies have Coins in their valves in order to lure a character close so they can attack them.
New Super Mario Bros. U
Clampies also appear in New Super Mario Bros. U where they act exactly like they do in New Super Mario Bros. Wii. They are very rare and only one can be found in a secret area of Waterspout Beach. They are also found in World Coin-5.
Mario Kart 7
Clampies appear in the Cheep Cheep Lagoon and Daisy Cruiser racecourses in Mario Kart 7 for the Nintendo 3DS. They are obstacles that are found only underwater, and like in New Super Mario Bros. Wii, they have Coins and Item Boxes between their valves that racers can pick up, taking care of not being trapped by the Clampy's valves.
Mario Party 10