From the Super Mario Wiki
Not to be confused with Clam
Clampies (also known as Giant Clams in New Super Mario Bros. U) are giant, purple Clam enemies that first appeared in New Super Mario Bros. Wii.
Super Mario series
New Super Mario Bros. Wii
They only appear in World 1-4 and in a secret area in 4-1. They will 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, and can be found in some levels of Sparkling Waters.
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
Clampies reappear in Mario Party 10 in the board Whimsical Waters. They also appear in the minigame Cheep Cheep Check, where they serve as distractions for the group players.
- A clam that serves the same function as the Clampies was first seen in the animated Mario film Super Mario Bros.: Peach-hime Kyushutsu Dai Sakusen! where it was seen keeping a captive Starman away from Mario by closing its shell and keeping the Starman in its valve. As a result, it may be possible that the Clampies may have been inspired from this early enemy.
- ^ Stratton, Steve (November 18, 2012). New Super Mario Bros. U: Prima Official Game Guide, page 79.