Clams are molluscs mentioned in the DreamWorks Dragons Franchise.
Clams are Molluscs in the Order Bivalvia, indicating they have two shells hinged together. Clam shells are generally equal in size and shape to each other.
|“||Mollusks like clams and oysters use calcium carbonate to construct a skeleton-like casing that is shells.||”|
|— Skulder in School of Dragons|
There are clam species that live in freshwater, but the majority of species live in salt water environments. Many have a strong "foot" with which to burrow into the sand or silt in their habitat. Some species live along the coastlines and emerge at high tide, then burrow into the sediment at low tide.
Giant Clams are mentioned or seen on multiple occasions within the Franchise. The Giant Clam (Tridacna gigas) is native to the South Pacific Ocean and the Indian Ocean in coral reef areas. It is presently endangered due to over-harvesting and habitat destruction. Though very large in comparison to most species of clams, the largest specimen found was measured at 4 feet 6 inches. This is smaller than what is seen in the Franchise, but nonetheless huge in real life. Historical Vikings would not have encountered this species at all.
Both in the Franchise and in reality, clams are seen as a food source for humans. Additionally in real life, clam shells sometimes serve as collectibles. Historically, some clam shells were used as beads and currency to some Eastern Native American tribes.
In "Dragon Eye of the Beholder, Part 2", the Dragon Riders have found the Dragon Eye and bring it back to Berk to figure out its purpose. As Gobber tries to unlock it, he harkens back to an old memory.
|“||I once opened a 500-year-old giant clam at the bottom of the ocean with my bare hook. Can I open it? Ha! I think it's going to be... Huh. Aha.||”|
|— Gobber in "Dragon Eye of the Beholder, Part 2"|
|“|| A poem for the modern woman.|
Hair, it smells of flounder.
Skin, rough like the coral of a thousand-year-old reef.
Lips, dry as jerky made from the giant clam.
No hand will be severed from this woman,
for she is modern.
She is Ruff.
She is Nut.
She is Ruffnut.
Clams are mentioned briefly in one of the "Farm Jobs" a player can complete by raising and harvesting crops for coins. This one involves growing tomatoes.
|“||Mulch wants to make soup with tomato base and clams.||”|
|— School of Dragons|
Later, during the release of the Expansion, "Wrath of Stormheart", giant clams are seen off the coast of Vanaheim. They are to be utilized by the player for underwater swimming, as they have captured air in their shells for breathing, in game. In reality it is extremely doubtful clams could be used in such a way, or have air pockets within their shells.