Why Should We Care About Clams?

Clams have been a part of Earth’s ecosystem for at least 500 million years as one of the first-ever complex organisms. Furthermore, they leave behind their hardened calcium carbonate shells on the ocean-floor which after millions of years, break apart, get buried under layers of sediment and finally, heat and pressure cement together with other sediments to form limestone, the building blocks of many a fine city building! Additionally, their shells are amazing and beautiful. Humans have found countless uses for them since ancient times to the present! And most importantly, they feed the world!

Identifying Your Clamshells: “Clam” can be a term that covers all bivalves, such as scallops, oysters, arks or cockles, to name a few. When identifying bivalves, look for color, size, shape, number of ribs, and the wings or ears that project from the hinge. I hope my article will help you identify something you couldn’t resist picking up from the sandy seashore!

• For additional clam info including various Arks, Angel Wings, Cardita to various Lucinas go HERE
• For additional clam info including Coquinas, Tellins, Various Oysters and more go HERE
• Otherwise, scroll to the “Categories” sidebar under “Seashells Clamshells” and all 38 species are described there as you scroll.

1. Atlantic Giant Cockle (Great Heart Cockle)

The Atlantic Giant Cockle, also known as the Great Heart Cockle (Dinocardium robustum) is a very beautiful bivalve displaying well-inflated, sturdy and large shells, taller than they are wide. It displays 32 to 36 radiating ribs and is commonly colored tan with reddish-brown patches on its outer shell exhibiting a deep pinkish interior. In general, Cockles or Heart Shells of the U.S. Atlantic coast are close relatives to the edible cockles of Europe. There are approximately 250 species worldwide.

Atlantic Giant Cockles use a strong foot to burrow into the sand or propel themselves across the sea bottom by pushing off and even jumping several inches. They require light to aid photosynthesis for their symbiotic algae. They are desired by shell collectors for their sturdy, attractive heart-shaped shells when both valves are clamped together. (See photo)

• Size: Up to 2 inches
• Habitat: Moderate shallow water in sand, mudflats, seagrass beds and rubble near reefs; intertidal zones to 65 ft (20 m)
• Range: Native from North Carolina to Florida to the West Indies, Brazil and Texas

Note: The Atlantic Giant Cockle or Great Heart Cockle is also known by some as Van Hyning’s Cockle, especially if you live in the state of Florida. In 1914, the Florida Museum of Natural History’s first director, Thompson Van Hyning, attempted to document Florida’s varied animal life. Today the museum houses a collection of 3 million mollusks including clams, snails, squids and octopuses.

2. Yellow Prickly Cockle

The Yellow Prickly Cockle or Yellow Cockle (Trachycardium muricatum) is a small, cherry round cockle displaying 20 to 40 radiating ribs over its shell’s exterior. The ribs near the beak area are smooth; those farther out from the beak display small spines. The outer shell is yellowish-white with a delicate white to yellow-tinted interior.

• Size: Up to 2 inches
• Habitat: Moderate shallow water, sandy or muddy botooms to depth of 35 ft (11m)
• Range: Native from North Carolina to Florida to the West Indies, Brazil and Texas

3. Florida Prickly Cockle

The Florida Prickly Cockle (Trachyardium egmontianum) shell is well-inflated, medium size possessing a white to tannish to light-brown exterior with a salmon, pinkish color or sometimes purple interior. The 27 to 31 radial ribs on the outer shell are more scoop-shaped compared to the Yellow Prickly Cockle’s.

• Size: Up to 3 inches
• Habitat: Gulfs and bays, sand-mud bottoms, seagrass beds in shallow waters to depths 50 ft (15 m)
• Range: North Carolina to Florida, and Texas

4. Eggshell Cockle

The Egg (or Eggshell) Cockle (Laevicardium laevigatum) shells at first glance may be mistaken for an egg by their elongated oval shape and smooth surface. The shell is rather thin and inflated with fine radial ribs delicately etched and undetectable by touch which gives the shell’s surface a smooth and polished appearance. The color is off-white, often tinged with brownish-orange, yellow or a hint of purple; the interior is white and sometimes slightly tinged with pink.

A fun note about this mollusk is that it has the ability to jump rather well. A shell collector reported that a live specimen he had captured in his boat even leaped to its freedom.

• Size: Up to 3 inches
• Habitat: Shallow water in sand or mud, seagrass beds where to feed to depths of 500 ft (155 m)
• Range: North Carolina to Florida and as far south as Brazil

5. Bay Scallops

Bay Scallops (Argopecten irradians) possess a fan-shaped exterior shell with a color ranging from bluish gray or purplish to yellow, white, brown or reddish-brown. The lower valve is commonly white and flatter. The interior of their valves are whitish, but often purplish near the hinge. They have inflated upper valves with 19 to 21 ribs which are squarish compared to “Calico Scallops” and may be banded. The wings are fairly even, but may be worn off.

When Bay Scallops are young, they attach themselves to objects such as eelgrass. This helps them avoid bottom-feeding predators, such as sea stars. As Bay Scallops grow, they drop to the sediment surface and move on to tidal flats to feed at high tide. Bay Scallops are the most common edible shellfish.

• Size: Up to 4 inches
• Habitat: Subtidal zones, eelgrass beds, sandy and muddy bottoms and offshore in shallow waters of bays and harbors to 30 ft (10 m) depths
• Range: Maine to Florida and the Gulf of Mexico

Scallops otherwise known as “pectens” have rows of tiny eyes along the edge of the mantle making them unique among bivalves. In general, the name, “scallop,” aptly describes the fluted edges of the animal’s circular fan-shaped shell.

Scallops move freely using jet-propulsion by flapping their valves with their large-strong hinge-muscle. Scallops lack the stretchy foot for digging, unique from most bivalves. Scallops are more common along the Atlantic Coasts than the Pacific. Early Native Americans used scallop shells in their ceremonial dances and some tribes used them as ornaments.

6. Zigzag Scallop

Zigzag Scallops (Euvola ziczac) display varying colored shells, rounded ribs that range from white to orange, yellow, gray and purple. The lower valve is somewhat cup-shaped, whereas the upper valve is fairly flat. The ear/wings are uneven. Their outers shells exhibit a zigzag pattern (enlarge above photo to see) of tiny or distinct stripes which gives the name. Zigzag scallops also move in a zigzag pattern when jetting. The interior valve is whitish and purple-brown halfway to the outer edge.

• Size: Up to 4 inches
• Habitat: Shallow waters near the shore and form beds in sandy or gravel substrates to depths of 150 ft (500 m)
• Range: North Carolina, throughout the Gulf of Mexico and the Caribbean and as far south as Brazil.

7. Lion’s Paw Scallop

Lions Paw Scallops (Nodipecten nodosus) formerly (Lyropecten nodosus) shells do not have the tendency to develop nodes on the ribs like other similar species. The shells can be colored white, brown, reddish and sometimes mauve to purplish showing some spots. Lion’s Paw shells display 9 to 10 broad radiating deep ribs with additional fine lines. Look for the wide copper interior banding around the perimeter.

• Size: Up to 4 inches
• Habitat: Fairly shallow water moderately exposed to sheltered reef systems, attached to corals and loose rubble; often located in deeper offshore areas, clinging to rocky substrates, crevices, or adjacent to rubble; depths to 500 ft (150 m) 
• Range: Atlantic coast of North America, ranging from North Carolina to Florida, the West Indies, including Brazil and Bermuda.

8. Calico Scallops

The pretty Calico Scallop seashells (Argopecten gibbus) are a favorite among collectors who strive to get the greatest variety of shadings. Some collectors have a hundred Calicos, all of different color combinations. Their mottled purple, orange, pink or even brown-hued shells commonly wash ashore, providing beachgoers with colorful treasures. They’re often found with their wings/ears broken off. The shells display 19 to 21 roundish ribs over their fairly dome-shaped valves.

A quick note about various seashells colors: Some shells turn a variety of colors after they die. These colors depend on the shells’ afterlife environment. Black shells were likely darkened by iron sulfide if buried in sulfurous muck. Pink, rust or brown are colors most shells turn after decades of exposure to air and sun.

• Size: Up to 3 inches
• Habitat: Although closely related to bay scallops, calico scallops live in deeper, offshore waters and are found on sandy or shelly sea-bottoms, 9 to 400 meters (30 to 1,200 feet)
• Range: Native from the coast of North Carolina to Florida, the Gulf of Mexico and the West Indies

9. Calico Clam (Checkerboard Clam)

Calico Clamshells (Macrocallista maculata) are another popular shell among collectors. They are also referred to as Checkerboard Clamshells or Spotted Clamshells. The shell has an exterior of creamy white with a checkerboard pattern of brownish-red. The interior is polished white with splashes of yellow or faint lavender. It has a moderately strong shell that is oval with very fine radial lines. They are edible.

• Size: Up to 2 1/2 inches
• Habitat: Shallow sandy coarse-sand bottom waters, off-shore seagrass bed to depths 60 ft (18 m)
• Range: North Carolina, Florida to the West Indies, Bermuda to Brazil

10. Sunray Venus Clam

Sunray Venus (Macrocallista nimbosa) has also been called the Giant Callista. Its outer valve is violet gray to tanish with darker streaks radiating out from the hinge. The interior is dull white with a tinge of red over the central area. Fresher specimens are more pinkish. It has an elongated oval-shaped shell with a glossy, smooth surface. Native Americans used the Sunray Venus shell as eating utensils. They are edible.

• The Venus Shell is named for the Goddess Venus and is noted for its graceful lines and beauty of color and sculpture.

• Size: Average is 3 inches, but can grow up to 4 inches
• Habitat: Sandy-mud ocean bottoms in shallow water intertidal zones to depths 180 ft (55 m)
• Range: Native to Florida’s West Coast, St. Petersburg to Marco, the beginning of the Everglades Islands and found as far north as North Carolina and west to Texas

11. Cross Barred Venus Clam

The Cross Barred Venus (Chione cancellata) is a small, roundish triangular clam with a shell marked by distinct radiating and crossover lines, giving it a miniature lattice-work appearance. The slightly inflated shell is whitish often with brown markings. The inner surface of the shell displays a deep purple color. Gather enough of these living clams and you can make a delicious chowder.

• Size: Up to 2 1/2 inches
• Habitat: More abundant in vegetative areas of shallow bays, often living in dense groups to filter-feed on plankton. 
• Range: North Carolina to Florida, south to the West Indies and east to parts of the Gulf of Mexico

12. Lady-In-Waiting Venus Clam

Lady-in-Waiting Venus Clam  (Puberella intapurpurea), formerly (Chione intapurpurea), displays a triangular, concave sturdy shell with distinct concentric ridges and vertical beads or ridges giving it a cross-hatched look. The lower margin or edge of the shell is serrated similar to teeth, notably visible from the interior. They have a prominent inward beak and are colored a pale yellow to off-white, sometimes with brown patches or freckles. If only I knew how this pretty little Venus clam got its name. In human culture, a “lady-in-waiting” is a female companion or personal assistant to a royal or noblewoman of high rank.

• Size: Up to 1 1/2 inches
• Habitat: Sandy bottom shallow water withing intertidal zones to depths of 280 ft (85 m)
• Range: North Carolina to Florida, as far south as Brazil and east to Texas’ Gulf Coast

13. Princess Venus Clam

The Princess Venus Clam (Periglypt alisteri) displays a heart-shaped shell with numerous fine concentric rings and fin distinct radial ribs over its exterior. It has a fairly inflated sturdy shell with a distinct serrated edge reminiscent of fine teeth, observed from the interior. I love this little seashell for its deep brown exterior color contrasted with its striking white interior. It is often accompanied with purplish stains.

• Size: Up to 2 inches
• Habitat: Buries in gravel, coral rubble, sand and mud in mid-intertidal zones to depths around 3 ft (1 m)
• Range: Florida to the Caribbean

14. Northern Quahog Venus Clam

The Northern Quahog (Mercenaria mercenaria)—pronounced “co-hog”—is a large, thick, sturdy-shelled clam, also known as a type of Venus Clam or hard-shelled clam. It’s often round to oval in shape and may be very plain or decorated with ridges of thin concentric, colorful lines or rays. The Northern Quahog is more colorful than its southern cousin, with a beautiful interior decorated with deep purple swirls.

The Northern Quahog was prized by Native Americans and was an important part of their diets. They used the shells to painstakingly make the colorful beads for “wampum” belts which served to bind treaties. The Native Americans also called the smaller ones “Littleneck” or “Cherrystone” clams. The Latin name “Mercenaria” is derived from a word that means wages and was given to the quahog due to the Native American use of wampum as money, trade and jewelry. The name “quahog” comes from the Native American name “poquauhock,” meaning horse fish.

• Size: Up to 6 inches
• Habitat: Offshore burrowing in sand, mud, or shell hash bottoms in shallow wate ranging from the high-tide line to about 60 ft (18 m) depth. 
• Range: Nova Scotia, Canada to Florida and east to Texas

15. Southern Quahog Venus Clam

The Southern Quahog (Mercenaria campechiensis)—pronounced “co-hog”—is a type of Venus Clam also known as hard-shell clams. Their shells are large, thick, sturdy and inflated displaying concentric ridges over their entire surface. The beak of the Southern Quahog shell grows inward toward the anterior. Their outer shells are grayish to brown to white. Their interior shell is chalky white, and lacks the purple characteristic of its cousin, the Northern Quahog, but can have hints of purple. They possess two muscle scars on the interior surface of each valve.

Quahogs are extremely efficient filter feeders, and large quahogs can filter about a gallon of water per hour. Quahogs are prized as food for humans and constitute one of Rhode Island’s most important fisheries.

• Size: Up to 7 inches and slightly larger than their cousins, the Northern Quahog
• Habitat: Burrows offshore in intertidal zones under sand, mud or shell hash bottoms to a water depth of 120 ft (36 m), and may also be found in salt marshes
• Range: Cape Cod, Canada to Florida, as far south as Cuba and west to the Gulf of Mexico and the Mexican Coastline

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