Bivalves - Seashells by Millhill

The bivalve seashells, or shells that come in two parts or halves, can be similar in appearance, but not all bivalves are clams or scallops.

I’ve gathered some photos of the more common bivalves I see on beaches and in the saltwater rivers around my area of Florida. A general bivalve list includes: clams, oysters, scallops, cockles and mussels.

The water that surrounds Florida provides sea snails with the perfect environments for life. Crashing waves are not friendly to shells, so many of the most beautiful shells are found on the Gulf coast. Most often the shells I find on the east coast are along the muddy saltwater riverbeds. This includes the calmer waters just inside the ocean inlet.

Clams and Arks

My photos below in this section contain various types of clam shells. Also, there are many types of Venus clams and loads of coquina clams. Shells called Arks are also clams.

Clam shells can be hefty and large, or thin and fragile. The Angelwing shell and Channeled duck clam are often found broken. They tend to break up in rough surf. Dosinia clams are smooth and thin, but strong. They are one of my most favorite seashell to find.

Tagelus bivalve clam — Tagelus clam shell

quahog clam living alive hefty shell — Tagelus clam shell

ark shell with brown stripes — Ponderous Ark

broad ribbed cardita shell underneath — Cardita flipped

broad ribbed cardita bivalve seashell — Cardita flipped

angelwing seashells — Angelwing shells 5″

angel wing white bivalve with caked on sand. — Angelwing shells 5″

Oysters

I rarely collect oyster shells but we see oyster beds while out on our boat. Oyster shells are sharp, and are the scourge of boaters because they can slice up the underside of the boat. But oysters are needed to keep oceans and rivers clean.

Oysters filter the water, and they grow in clumps that give sea snails, crabs and fish a place to hide and live. While walking the flats in oyster areas I can hear the shells snapping. You can read more about oysters at OneEarth.org.

oysters attached to tree roots — Oyster Shells

Scallops – Bivalves With Color

Scallop shells can be some of the prettiest shells. Certain types of scallops have one flat side and the other is normal / rounded. The concave part is in the sand or bottom and the flat part is on top and opens like a flap when the scallop is alive. Scallops propel themselves around by opening and closing their shells.

The Kitten Paw and larger Lion’s Paw (don’t have) shells are also scallops. I found these Kitten Paw shells while visiting Sanibel Island on the Gulf coast. I’ve never seen any where I live on the east coast.

Types of scallop shells — 2 inches across

kitten paw seashells — Kitten’s Paw Scallop Shells

Cockles – Bivalves With Color Inside

Cockles are not clams although they look similar. Because they have an oval shape with high top part (umbo), when a whole cockle is viewed from the side it resembles a heart. For that reason, they are known as the heart shell or heart cockle.

Most often these bivalve shells are often found open and partially buried in the mud. Even if the two halves are attached, usually as they dry out they will come apart.

An open shell resting on a sandy surface with a small hole nearby. — Bivalves

bivalve cockle shells — Atlantic Giant Cockle Shell

inside the giant cockle shell — Atlantic Giant Cockle Shell

Mussels

Mussel shells are something I rarely collect or photograph because they really are not great looking shells. The pen shell is distantly related and I have a few pictures here. The pen shell can be nearly a foot in length and is more impressive than a mussel. Read a lot more about Pen shells at the Sanibel Captiva site.

mussel seashell — Open and empty mussel shell

part of a pen shell on the beach sand — Pen shell piece

More about the shells

Big Seashells Found in Florida

Sharing some photos of the big seashells I’ve discovered while beach-combing along the Indian River.

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Pretty Gray Banded Tulip Shell

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Shells Found on a Deserted Beach

Found lots of knobbed whelks on this deserted island beach in Mosquito Lagoon. And a few other pretty shells.

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Collecting Seashells: Grouping the Bivalves

The bivalve seashells, or shells that come in two parts or halves, can be similar in appearance, but not all bivalves…

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Scallop Shells Collected on the East Coast

While photographing my newly collected shells the other day, I decided to re-photograph my pretty scallop shells. Florida waters can contain…

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A Rare Find For Me, The Bubble Shell

The bubble shell is immediately recognizable by the wide open curl at the bottom of the aperture. The shell I found…

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The cockle shell is easy to confuse with the ark shell. Arks are the ones you are most likely to find along Florida’s east coast beaches. Both types live in the sand near beaches, so it figures that their empty shells would be washed up on shore once the mollusk dies.

Arks are fairly small in comparison to the Atlantic Giant Cockle, pictured here. The Giant Cockle can grow to be 5.5 inches.

Inside the giant cockle shell, which is mauve pink in color. — Once cleaned up, the inside of the giant cockle is mauve pink.

The shape of the giant cockle when closed, makes a heart. Therefore, it is also known as the “heart cockle”.
Sorry, my shell is not very pretty, but you can see the heart shape.

heart cockle seashell — The giant cockle is also called the “heart cockle”

Ark shells begin white, and can change color. Shells that are brown, rust color, pinkish and yellow, turn that way from long term exposure to the air. Black shells have darkened because of iron sulfide in the sand in which they are buried.

Arks don’t grow as large as the giant cockle, with their max size being around 4.5 inches (the Cut-ribbed ark), but the ones I find are 1-2 inches. Within the ark population there are various types of arks, which I will get to later on in this blog. But all arks can be found on all Florida beaches.

A group of colorful ark seashells in off-white, beige, rust brown, gray and black. — Ark shells can be colorful

Although I find both types of shell often, the larger cockles are usually spotted away from the area of the crashing waves. I find the big ones, usually still hooked together, out on the flats in the backwater areas at low tide.

cockle shells and arks in different sizes and colors — Can you find the 3 cockle shells in this photo?

The arks and cockles resemble each other, unless you look closely. Arks tend to curve a bit at the top. Below I have one of each type side-by-side. They are similar in color and size, but it should be apparent that they are not the same type of shell. Read more about common seashells found on Florida’s east coast.