Oysters, but very very rarely they are found in clams.
Pearls are produced by Oysters.
they usally have fins
Eels. Eels do not typically have pectoral fins (general area of animalia arms), nor do they have pelvic fins (the general animalia area of legs). Dorsal and anal fins are typically fused along the back around the tail and over the belly with the caudal fin a a ribbon-like structure.
The animal that hides sparkling pearls is the oyster. Oysters produce pearls as a defense mechanism in response to an irritant, such as a grain of sand, that enters their shell. Over time, layers of nacre are deposited around the irritant, forming a pearl. Click the link below to get more views on Dogs and pets
Without doubt that would have to be the squid, specifically the Colossal Squid. This animal grows to 14 metres (46 ft), and its eyes are the size of beach balls. It not only has the largest eyes of any sea dwelling creature, but but it has the largest eyes in the whole animal kingdom!
The fins act as stabilizer's. When the snake would make "S" movements in the water it was hard for it not to flip over at some point. So, it has developed fins on its back to works as a stabilizers which help to keep it right-side-up.
I do not know of any mammal (mammals are the only animals to have hair) that has fins (fins are the preserve of fishes), but a sea-lion is an animal that is covered in hair and has "flippers".
Oysters. Actually, clams and certain other molluscs can also produce pearls, but it's only oyster pearls that are of gem quality.
they usally have fins
The pearls aren't in the Sea of Monsters. They are in the first book.
Bivalve crustaceans such as oysters have pearls.
The places to purchase South Sea pearls online are many and varied. A good place to start would be Pearl Paradise, Raw Pearls, Premium Pearls and Pearl Gallery.
Imitation pearls made from sea shells; very popular on Okinawa.
Eels. Eels do not typically have pectoral fins (general area of animalia arms), nor do they have pelvic fins (the general animalia area of legs). Dorsal and anal fins are typically fused along the back around the tail and over the belly with the caudal fin a a ribbon-like structure.
Oyster
clams
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oyster