What’s the difference between oysters, clams, mussels, and scallops?

Oysters, clams, mussels and scallops – aren’t those all the same thing?!

Close – these animals all belong to the mollusk family, and have lots of similarities. Are all members of the mollusk family, which includes any invertebrate having one, two or more shells that wholly or partially enclose their soft, unsegmented body. Other mollusks you may know are snails, squids and octopuses. Oysters, clams, mussels, and scallops are all commonly farmed or harvested for food and they all also have the ability to produce a pearl, although the types of pearls they can produce are all very different. To learn more about some amazing naturally formed pearls (from more than just oysters!) Check out our awesome Natural Pearls blog to help shed some more light on the differences between some of the mollusks mentioned in this blog.

So now that you know how they’re similar, let’s get to why you’re really here: to learn how they’re different. Lets break it down:
According to dictionary.com, an oyster is any of several edible, marine, bivalve mollusks of the family Ostreidae, having an irregularly shaped shell, occurring on the bottom of or adhering to rocks or other objects in shallow water.

A clam is any of various bivalve mollusks, especially certain edible species.

Mussels are any bivalve mollusk, especially an edible marine bivalve of the family Mytilidae and a freshwater clam of the family Unionidae.

And scallops are any of the bivalve mollusks of the genus Argopecten (Pecten) andrelated genera that swim by rapidly clapping the fluted shell valves together.

Still confused? Lets compare them side by side.
Clams and scallops can move about in their environment, while mussels and oysters are rooted into wherever they attach their shell. As mentioned in the dictionary.com definition above, scallops move by clapping their shells together. Here’s some video proof:

Clams move by opening their shell and sticking out a large foot that they use to push themselves along the surface with. As seen in the following video, the “foot” actually looks more like a huge tongue! They really are neat animals.

Mussels also have feet, although they prefer to remain attached to their substrate.

Wild oyster shells are typically rough, dull, and covered in barnacles.
Wild oyster shells are typically rough, dull, and covered in barnacles.

In appearance, all are very similar. Oysters typically have round or oval shaped shells, mussel shells are more oblong, clam shells are typically more short and squat in shape, and can be smooth or have wide waves as seen in the giant clam.

Short, round clam shells
Short, round clam shells.

Scallops have the iconic sea-shell shape.

Colorful scallop shells
Scallops come in a range of colors.

These animals exist in a wide range of sizes, but mussels typically are the smallest of the mollusks, averaging only a couple inches across.

A bed of mussels
A bed of mussels. They are typically small and come in a wide range of colors.

The average size for scallops are two to three inches, with the largest species being the deep-sea scallop at five or six inches across. Oysters and clams, on the other hand, can grow to be huge! The largest oyster discovered was around 15 inches, and giant clams can reach a whopping six feet in length. In fact, one of these massive clams actually produced a fourteen pound pearl.

This example of a giant clam has a large, ridged shell.
This example of a giant clam has a large, ridged shell.

Although all of these mollusks are similar, all have their own roots or traditions.  Clams were worshiped by the Moche people of ancient Peru and used as money by the Algonquin Indians. Scallops symbolize femininity in many cultures. The outward shell represents the protective and nurturing ability that a mother possesses. The famous painting of the Roman goddess of love and fertility, Venus, painted by Botticelli includes a scallop shell. Also, in ancient cultures a young couple desiring to bear offspring had to make a pilgrimage and often carried a scallop shell as a symbol of gaining fertile abilities. In Christianity, the a scallop shell is often seen as a symbol of a pilgrimage, thanks to the use of a scallop shell by the apostle St. James the Great, who traveled with a shell and would only ask those he met for enough to fill the shell – whether it be a small drink of water or a mouthful of food. The scallop shell now also appears in many pieces of religious Western art.

Fascinated by the world of oysters and their mollusk cousins? You may be interested in opening your own oyster at home!

4 thoughts on “What’s the difference between oysters, clams, mussels, and scallops?

  1. WoW! I was really impressed by your information! Thanks so much for sharing. I have a MUCH better understanding of the differences of these creatures and I will be far better able to share with my class! Thanks!

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