Bivalvia is a class of two-shelled mollusks including clams, oysters, and scallops. Most of these animals are tiny and virtually harmless in Real Life. However, fiction tends to make them more dangerous, by having them snap at people with their shells. Depending on the clam's size, it may either simply bite the victim, or actually "eat" them, trapping them inside its shell.
This portrayal is most likely inspired by the giant clam, Tridacna gigas. Of course, they don't actually eat people, but with their enormous size and scalloped shells giving them a somewhat sinister appearance, it sure looks like they could. As a result, many Clam Traps, if not explicitly called giant clams, will at least be modeled after them.
How anthropomorphized the clams are tends to vary, too. They may be given features such as eyes on their top shell, or a tongue inside their shells; sometimes their eyes are inside their shells as well. They can also range from mindless and neutral to sentient and evil — all that matters is that they bite.
In video games, expect to see them as obstacles — usually Invincible Minor Minions — in Under the Sea levels. They will usually open and close their mouths periodically, with a valuable item in their "mouth", forcing the player to swim in and grab the item before the clam shuts.
Subtrope of Artistic License Biology. Not to be confused with Bear Trap, a steel, somewhat clam-shaped device used to trap bears and other land animals. Often overlaps with Perplexing Pearl Production, if a bivalve snaps at someone who tries to take its pearl. Possibly averted by Palate Propping, although technically bivalves don't have a palate.
- Blake and Mortimer: When chasing Olrik underwater, Blake rescues him from a giant octopus attack, but then gets his foot stuck in a giant clam.
- In Pinocchio, Jiminy Cricket asks a clam about Monstro the whale, but it snaps shut and traps him inside. He gets out inside a bubble as the clam digs down.
- One encounter in the French gamebook series La Saga du prêtre Jean has a massive underwater clam trapping Prester John while he's swimming in an underground river in Solomon's Mines. You must either fight the thing in a limited amount of time (and get a precious pearl as a reward) or force it open with a vial of vinegar (which, however, spoils the pearl).
- There's a Chinese story about a snipe getting its beak caught in a clam when attempting to eat it. Since neither bird nor clam were willing to let go, a passing fisherman took advantage of their deadlock and caught both of them in a net. This led to An Aesop where a mutually-destructive battle between two parties leaves them open to a third party to take advantage of them.
- Happens to a deep-sea diver in the prequel tie-in novel for King Kong (2005). In this case, it's actually an oyster — an oyster the size of a dining table, in keeping with nearby Skull Island's wildlife gigantism — and the diver's foot got caught because he was walking backwards to try and avoid a Giant Enemy Crab without toppling over in his awkward hard-hat suit.
- In the 1960s Batman series, Robin gets "eaten" by a clam just before one of the Cliff Hangers. He is eventually rescued, of course, and that night Aunt Harriet cooks clam chowder, which Batman suggests could count as a manner of revenge.
- In the Doctor Who story "Genesis of the Daleks", Harry Sullivan manages to accidentally step into a giant terrestrial mollusc that Davros created, and get trapped by it. Despite them being somewhat immobile.
- On Good Eats, a town is being terrorized by a vicious scallop (in a parody of Jaws). Alton explains at the town assembly that it's physically impossible for a scallop to do that, but the townsfolk will have none of it. Later, it's revealed that the man attempting to catch the scallop made the whole thing up to draw in tourists.
- Mystery Science Theater 3000: In "Samson vs. the Vampire Women", Mike tries to eat a clam, only for it to snap down on the crackers he placed on it, then his fork, and then, when he takes a close look at it, his nose.
- Dungeons & Dragons module EX2 The Land Beyond the Magic Mirror. During the adventure, the PCs can go diving in order to harvest oysters. While doing so, there's a chance they'll be attacked and trapped underwater by giant clams. If they can't free themselves, they'll drown in 2-5 minutes.
- One of the (many) forms of hostile wildlife found in the Warhammer 40,000 Gaiden Game Necromunda is the Ash Clam, a mutated terrestrial bivalve native to the ash wastes of the titular planet, and occasionally found in more run-down areas of the underhive as well. These creaturesnote essentially function as a biological Bear Trap, which can lead to an ignominious end for any ganger unfortunate enough to get stuck in one.
- Magic: The Gathering has the Giant Oyster. It can clamp onto a tapped creature and keep it tapped (which prevents it from doing much) while also slowly killing it by putting a -1/-1 counter it each turn. It can also release the creature, which removes all -1/-1 counters from it. Presumably, the idea is that the clamped creature slowly drowns, but is able to swim back to the surface for air if released.
- The Deluded Depths from Alice: Madness Returns feature deadly clams that use bottles, teeth or memories to lure Alice into their shells, only to close up on her and kill her should she stay too long.
- Club Penguin: In the game "Aqua Grabber", a giant clam will close down on the player if they take its pearl, causing them to lose air, unless they pull a Weight and Switch with a pearl-shaped rock.
- Maneater Clams in Dark Souls I are giant legged clams that attempt to swallow you, doing massive damage.
- Feeding Frenzy: The clam at the bottom of the screen will occasionally open, revealing a pearl that your fish can take for bonus points. Beware, though, because when the clam closes its shell while you're on its mouth, you'll die instantly.
- Averted in the Glider PRO Game Mod "SeaCaves," in which clams open and close their shells (a graphical replacement for the original game's basketballs) constantly but never very far.
- In several games of The Legend of Zelda series, there is a recurring aquatic enemy known as Shell Blade, which is a huge clam that snaps at you or charges forward to ram the player, is defeated by hitting the soft parts inside the shell when it opens up, and is hellishly loud when moving.
- Mega Man Zero: In aquatic levels, you can sometimes find robotic clams that will try to bite you. You can only attack them when they're opening their shells.
- In Pikmin, one of the enemies is the Pearly Clam Clamp, a clam that opens its mouth when the Pikmin attack the pearl it is protecting (or in one case, the Radiation Canopy, one of the pieces of Captain Olimar's ship, The Dolphin). If the Pikmin aren't called back fast enough, the Pearly Clam Clamp will close its mouth over them and eat them, even doing so after they've recovered its pearl. The pearl it guards can produce 50 Pikmin when brought back to one of the Onions.
- Shellder and Cloyster, which look like scallops and oysters respectively, can do this with the Clamp move. This was their signature move until Ruby and Sapphire introduced Clamperl, another clam mon that could learn the move.
- A Shellder doing this to a Slowpoke's tail is the trigger for its evolution into Slowbro. Lore-wise, anyway; in gameplay Slowpoke simply evolves at level 37.
- In the 1983 ZX Spectrum game Scuba Dive giant clams could trap you if they close while you try to steal the pearls from them.
- Super Mario Bros.:
- New Super Mario Bros. Wii: There is a rare enemy called Clampy, a beautiful shimmering clam that opens its mouth to reveal a coin. But if a player swims in to grab it, Clampy can snap shut, trapping the player inside for a few seconds before spitting them out, causing the player to take damage.
- In Super Mario 64, clams can be found in Jolly Roger Bay, often with coins in their mouths. If Mario is in the clam when its shell shuts, he'll be knocked aside and take damage.
- In Super Mario Sunshine, there is a ride at Pinna Park containing several giant clamshells. Mario can open one by spraying it with water, and climb into its shell, but if he lingers too long, the clam snaps shut, hurting him.
- Some levels in Tasty Blue feature three clams. From time to time, they will open their shells. The player character needs to eat their pearls to grow bigger, but if the player character is too close to a clam when it shuts, they will take damage, causing them to shrink a little.
- The Cove area in Darkest Dungeon features gigantic oysters as curios. Interacting with them without using a shovel or dog treat has a chance for it to close on a hero's arm and leave them bleeding severely.
- In the "Ghost Writers" episode of Casper the Friendly Ghost, at the end the writing staff for Casper (it's a rather meta episode) spitball ideas for episodes, including "maybe a giant clam tries to swallow Casper!".
- In the Mickey Mouse (2013) short "Wonders of the Deep", Professor Von Drake is swallowed by a giant clam and Mickey and Donald try to save him.
- SpongeBob SquarePants:
- Sandy is introduced fighting a giant clam in her debut episode "Tea at the Treedome".
- In "Valentine's Day", Sandy is flying a hot air balloon made of chocolate when a flock of scallops tries to eat it, in an underwater variation of Balloon-Bursting Bird.
- In "Clams", a giant clam eats Mr. Krabs' millionth dollar. In trying to get it back, he gets eaten by it, but fights it and gets back his dollar... at the cost of the lower half of his body ("Nothing important").
- At the end of the Looney Tunes short "Ali Baba Bunny", a shrunken Daffy Duck is trapped inside a clam trying to get the pearl inside.
- In The Perils of Penelope Pitstop episode "Bad Fortune in a Chinese Fortune Cookie", Penelope is caught by a giant clam after the Bully Brothers tie her to an anchor and throw her into the water.
- One episode of The Land Before Time TV series has Littlefoot getting his face caught by a "snapping shell". It then latches onto Chomper's snout after getting pulled off, but he takes it off and eats it.
- Supposedly, giant clams sometimes close around divers' ankles and trap them. But there's scant evidence of this event ever actually happening and the closing is usually slow enough for one to withdraw their foot in time. Adding fuel to the fire is the fact that such clams do occasionally produce proportionately immense pearls, leading to the common myth that pearl divers would try retrieving the pearl from the clam and get trapped.
- While there's little evidence of this happening to humans, it definitely does happen to seabirds. To be fair, this is more a case of the bivalve desperately defending itself from a seabird determined to eat it than vice versa.
- The snuffbox is a type of freshwater mussel with jagged "teeth" along the edge of its shell that deliberates lures common logperch into its shell with a fish-shaped lure. When the logperch is lured, the mussel clamps down on its head and sprays it in the gills with parasitic larvae before letting it go (the logperch seems to be its primary host species simply because it's one of the few fish species strong enough to survive the experience). Basically the bivalve equivalent of a facehugger.
- Scallops are actually able to swim short distances by clapping their shell halves together, giving the appearance of a (completely harmless) snapping mouth.