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Clam Identification and Facts (From Arks to Tellins)

Kathi was a natural sciences teacher and now writes about fossils and other earthly subjects, including clams.

Read on to learn about 19 varieties of clams, including photos, identifying information, and interesting facts.

Read on to learn about 19 varieties of clams, including photos, identifying information, and interesting facts.

Identify Your Clams

The word "clam" can be used to cover all bivalves such as scallops, oysters, arks, and cockles, to name a few. Did you know that there are more than 15,000 species of clams around the globe? Amazing, right?

I hope to help you in identifying those clams you couldn't resist picking up at the beach. If you're not an active collector, I hope you just enjoy the beauty of the photographs and your curiosity while reading the information below. This article includes identifying information and interesting facts about the following 19 clams:

  1. Ponderous Ark
  2. Blood Ark
  3. Transverse Ark
  4. Incongruous Ark
  5. Cut-Ribbed Ark
  6. Zebra Ark
  7. Broad Ribbed Cardita
  8. Angel Wings Clam
  9. Disc Dosinia Clam
  10. Atlantic Surf Clam
  11. Eastern Oyster
  12. Digital Thorny Oysters
  13. Atlantic Thorny Oysters
  14. Spiny Jewel Box Oysters
  15. Jingle Shell Oysters
  16. Kitten Paws
  17. Tampa Tellins
  18. Speckled Tellins
  19. Coquina Clam
Ponderous Ark Seashell Collection (Noetia, ponderosa)

Ponderous Ark Seashell Collection (Noetia, ponderosa)

1. Ponderous Ark

Ponderous Ark (Eontia ponderosa) has a very thick triangular shell with strong flat ribs and a large beak that turns back to the rear of the shell. These arks have a dark velvety skin worn to white after beaching, and the calcareous shell can later stain to rust or gray.

Their robust shells make them and their relatives, such as the Blood Arks, among the most common beach finds where other bivalve shells are otherwise pulverized in high-energy wave zones.

Ponderous Ark and its relatives are a family of small to large-sized edible saltwater clams in the family Arcidae.

Size, Habitat and Range

  • Size: Up to 3 inches
  • Habitat: A sand dweller in shallow shores
  • Range: Virginia to Key West and the Gulf of Mexico
Ponderous Ark Showing Dark Brown Protective Covering called, Periostracum

Ponderous Ark Showing Dark Brown Protective Covering called, Periostracum

Camouflaging Layer Over Arks — The Periostracum

The shells of many ark species have a thick layer of a dark brown velvety covering called the periostracum. The photo above clearly shows this covering layered over the Ponderous Ark, which has partly been worn away. It serves as a protective camouflage over the harder calcareous part of the shell. After beaching, the periostracum begins to wear off and, in time, can completely disappear.

Blood Ark Seashells (Anadara, ovalis)

Blood Ark Seashells (Anadara, ovalis)

Comparison: Ponderous Ark Shells (left) and Blood Ark Shells (Right)

Comparison: Ponderous Ark Shells (left) and Blood Ark Shells (Right)

2. Blood Ark

Blood Ark (Anadara ovalis) derives its name from its uncommon red blood; most mollusks have clear blood. Like their close relative, the Ponderous Arks, Blood Arks have very thick shells, only to a slightly lesser degree.

At first glance, it's hard to tell apart the Blood Ark from the Ponderous Ark. The Ponderous Ark has a more triangular-shaped shell with an inflated high crease from the beak, whereas the Blood Ark has a more elongated oval shape (observe the comparison photo above). Also, the hinge line of the Blood Ark is slightly longer and straighter.

Size, Habitat and Range

  • Size: 2 1/2 inches
  • Habitat: Sandy shallows
  • Range: Cape Cod, Massachusetts to Florida and east to Texas
Transverse Ark Seashells  (Anadara, transversa)

Transverse Ark Seashells (Anadara, transversa)

3. Transverse Ark

Transverse Arks (Anadara transversa) are fairly sturdy, elongated oval and small bivalves. Their valves are somewhat inflated, bearing a relatively long straight hinge line.

They have squarish ribs and are usually colored white once the periostracum covering wears off after beaching. Like many seashells, they can stain rust or gray after prolonged exposure to the sun and air.

Note: On Florida beaches, they litter the shores.

Size, Habitat and Range

  • Size Up to 1 1/4 inches
  • Habitat: Gulf and bay sandy bottoms or hard substrates
  • Range: Massachusetts to Florida, east to parts of the Gulf of Mexico and south to the West Indies
Incongruous Ark Seashells (Scapharca, brasiliana, formerly, Anadara, brasiliana)

Incongruous Ark Seashells (Scapharca, brasiliana, formerly, Anadara, brasiliana)

4. Incongruous Ark

The desirable Incongruous Ark (Scapharca brasiliana, formerly Anadara brasiliana) is a sturdy-shelled ark distinguished by obvious beading on its strong radial ribs. They grow in a triangular shape with well-inflated valves and a strong beak turned back. Color is white with brown furry covering while alive and may discolor after being beached.

Size, Habitat and Range

  • Size: Up to 3 inches
  • Habitat: Gulf and bay sandy bottoms
  • Range: North Carolina to Brazil
Cut Ribbed Ark Seashells (Anadara, floridana)

Cut Ribbed Ark Seashells (Anadara, floridana)

5. Cut-Ribbed Ark

Cut-Ribbed Ark (Anadara floridana, otherwise known as Anadara secticostata) have fairly inflated shells with an elongated, slightly uneven oval shape. Their hinge is long and straight.

Usually colored white, but like other arks, they are susceptible to staining rust after beaching. The valve consists of 30-38 radial ribs flattened on top with a groove down the center of each rib and concentric ridges between the ribs.

Size, Habitat and Range

  • Size: Up to 4 1/2 inches
  • Habitat: Offshore sands, but closer to shore in Southern Florida
  • Range: North Carolina, Florida and the Gulf of Mexico to Texas and the West Indies

6. Zebra Ark (Turkey Wing Ark)

Zebra Arks or Turkey Wing Arks (Arca zebra) have an unusually elongated oval shape with a long straight hinge. The surface of the valve is uneven with rough-textured ribs. Still, their most distinguishing mark is the attractive zigzag alternating brown and white stripes resembling a zebra or, obviously, a turkey wing.

This ark shell has also been called “Noah’s Ark” because of its shape when the valves are connected. Like many arks in general, living examples are covered with a thick and bristly “carpet” or periostracum that wears away after beaching.

Size, Habitat and Range

  • Size: Up to 3 1/2 inches
  • Habitat: The mollusk attaches itself by its byssus (threadlike filaments) to rocks and other solid objects in shallow water
  • Range: North Carolina to the West Indies, and also on Bermuda’s shores, as well as in the Mediterranean
Broad-Ribbed Cardita Seashells (Carditamera, floridana)

Broad-Ribbed Cardita Seashells (Carditamera, floridana)

7. Broad-Ribbed Cardita

Broad-Ribbed Cardita (Carditamera floridana) is also known as the Bird Wing. The exterior shell is white with purple or chestnut blotches with a white interior. The shell is oval, small and thick, with 20 strong raised and beaded radial ribs.

Jewelry makers love this little shell which washes ashore commonly on Florida beaches.

Size, Habitat and Range

  • Size: Up to 1 1/2 inches
  • Habitat: Attaches itself to the substrate by means of its byssus (threadlike filaments) in sand or mud 3 to 25 feet deep
  • Range: Florida east to Texas and Mexico
Angel Wing Seashells ( Cyrtopleura, costata)

Angel Wing Seashells ( Cyrtopleura, costata)

8. Angel Wings

Angel Wing clams (Cyrtopleura costata) have lovely elongated, wing-like valves with 26 radiating ribs finely sculptured, intercepting with a series of concentric growth rings parallel with the margin. Angel Wings are typically white and sometimes tinged pinkishly.

The muscles on their hinges are relatively weak, so it's uncommon to find the left and right valves connected. Also, their valves are rather thin and brittle, so they're often found damaged from rough seas.

Interestingly, Angel Wing shells will glow if exposed to ultraviolet light. They can extend a long siphon that protrudes from the burrow used to circulate water and draw in food particles with enough strength to bore into clay, wood and even shale.

Size, Habitat and Range

  • Size: Up to 7 inches
  • Habitat: Shallow water burrowing up to three feet deep in mud, clay or peat
  • Range: Cape Cod to Florida and the Gulf of Mexico, east to Central America and as far south as Brazil
curious-collectors-of-clam-shells-cont

9. Disc Dosinia

The Disc Dosinia clam (Dosinia discus) has an exterior valve and is yellowish-white with a pure white interior. The valves are moderately thin and circular in outline with a small dominant beak.

A distinct feature of Disc Dosinia is the fairly even concentric ridges of about 20 to 25 per inch. Another species, Elegant Dosinia, has about 50 ridges to the inch.

Size, Habitat and Range

  • Size: Average 2 inches, up to 3 inches
  • Habitat: Just offshore in moderately shallow water and paired valves are often commonly found
  • Range: Virginia to Florida, east to the Gulf States and south to the Bahamas
Atlantic Surf Clam Seashell (Spisula, solidissima)

Atlantic Surf Clam Seashell (Spisula, solidissima)

10. Atlantic Surf Clam

The Atlantic Surf Clams (Spisula solidissima), also known as Hen Clam, Bar Clam, Skimmer Clam, or Sea Clam, prefer the surf environment on sandy shores feeding on minute plant and animal life washed back and forth by the waves.

Their valves' outer surfaces are colored white to yellowish-white, sometimes with added gray. They are triangular-shaped and possess thin concentric growth lines. They grow fast and large and are prized by humans for their sweet flavor.

U.S. wild-caught Atlantic Surf Clam is a smart seafood choice because it is sustainably managed and responsibly harvested under U.S. regulations.

After severe storms, beaches are sometimes covered with millions of these clams, and people often pick up a large empty shell to dig in the sand or take home as a decorative dish.

They can live up to 35 years.

Size, Habitat and Range

  • Size: Up to 3 inches
  • Habitat: Warm coastal water near shore, typically in surf waters
  • Range: Predominantly from Nova Scotia, Canada to North Carolina and as far south as Florida to portions of the Gulf States
Eastern Oyster Seashells (Crassostrea, virginica)

Eastern Oyster Seashells (Crassostrea, virginica)

11. Eastern Oyster

The Eastern Oyster (Crassostrea virginica) can go by several names, including, Wellfleet Oyster, Atlantic Oyster, Virginia Oyster, or American Oyster. The shell is heavy and possesses a teardrop-oval shape that varies greatly. Sometimes they have scaly concentric layers over their outer surface, and sometimes with irregular concentric rings, and yet sometimes with irregular vertical ribs. It's interesting to note that they can grow to any shape necessary.

The Eastern Oyster varies in color from white to gray to tan, or with pinkish markings. The right or top shell is flat with a purple muscle scar on the interior, while the bottom shell is cupped, with a dark muscle scar.

Eastern Oysters are very popular commercially. Today, less than 1% of the original 17th-century population (when the original colonists arrived) is thought to remain in the Chesapeake Bay and its tributaries. The Eastern Oyster is the state shellfish of Connecticut, and its shell is the state shell of Virginia and Mississippi, and the shell in its cabochon form (polished) is the state gem of Louisana.

Eastern Oyster Seashells showing interior abductor muscle scar and rough exterior

Eastern Oyster Seashells showing interior abductor muscle scar and rough exterior

Eastern Oyster Quick Facts

  • Eastern Oysters have fast growth and reproductive rates.
  • First mature as males, then later develop female reproductive capabilities.
  • An adult oyster can filter up to 50 gallons of water in one day.
  • Oysters can live out of the water during cooler months for extended periods.
  • These oysters often attach to one another, forming dense reefs that provide habitat for many fish and invertebrates.
  • They are sought after for their creamy white meat and firm texture with a mild, sweet flavor.

Size, Habitat and Range

Size: Average 3-5 inches, Up to 8 inches

Range: Brackish and saltwater from shallow bays 8 to 35 feet deep, often concentrated in oyster beds or rocks

Habitat: From Nova Scotia, Canada, south to Florida, east to the Gulf of Mexico and further south as far as Venezuela

Digitate Thorny Oyster Seashell (Spondylus, tenius)

Digitate Thorny Oyster Seashell (Spondylus, tenius)

12. Digital Thorny Oysters

Digital Thorny Oyster (Spondylus tenuis) is often mistaken for the Atlantic Thorny Oyster (Spondylus americanus). There are many species of Thorny Oysters from the genus Spondylus, and they vary considerably in appearance and range. They are also known as Spiny Oysters.

However, they are not true oysters, yet they share some habits such as cementing themselves to rocks rather than attaching themselves by a byssus, like most bivalves. Also, the two halves of their shells are joined with a ball-and-socket hinge rather than with a toothed hinge, which is more common in other bivalves.

They have thick lumpy shells most often with thorns, although the Digitate Thorny Oyster has fewer than most. Some varieties are whitish, pink, reddish or orange. Interior is whitish with darker band around the perimeter.

Note: The example above of the Digitate Thorny Oyster has a tubeworm casing attached to it.

Size, Habitat and Range

  • Size: Average 3 inches, up to 5 inches
  • Habitat: Attach to coral reefs or rocky reefs depending on species in shallows or in deeper waters
  • Range: North Carolina around Florida to Texas, southwards to Venezuela and Brazil
Thorny Oyster Seashell (Spondylus, americanus)

Thorny Oyster Seashell (Spondylus, americanus)

13. Atlantic Thorny Oyster

Atlantic Thorny Oyster (Spondylus americanus) normally shows the telltale protruding thorns, but some lose their thorns due to wind and surf, which could be a possible explanation for the above sample.

It's a rather pretty specimen with the telltale reddish and yellow coloring. It has a pitted surface with an oval shape and is quite sturdy.

Size, Habitat and Range

  • Size: Up to 5 inches
  • Habitat: Deepwater reefs, especially in areas with high sedimentation. It is often lodged in a crevice or concealed under an overhang
  • Range: North Carolina and Texas southwards to Venezuela and Brazil
Spiny Jewel Box Oyster Seashells (Arcinella, cornuta)

Spiny Jewel Box Oyster Seashells (Arcinella, cornuta)

14. Spiny Jewel Box Oysters

The Spiny Jewel Box Oyster (Arcinella cornuta) bivalve attaches one of its shells to an offshore rock or substrate. This answers why beachcombers rarely find these beautiful bivalves in their full glory with both valves attached.

Look for a thick, strongly curved shell with knobs or longer spikes along 7-9 rows of spines. They're white outside, pinkish inside. I also have a golden sample presumably stained due to exposure to sun and air.

Fresh specimens have extended spikes and resemble the thorny oyster. The spikes become worn down by the surf and sand or can break off entirely.

Size, Habitat and Range

  • Size: Up to 2 inches
  • Habitat: Attached to rock, coral or shells in warm shallow water (sometimes in deep water) and exposed to air during low tide. Later in life, they become detached
  • Range: North Carolina to Florida and the Gulf of Mexico
Jingle Shells Oysters (Anomia, simplex)

Jingle Shells Oysters (Anomia, simplex)

15. Jingle Shell Oyster

The Jingle Shell Oyster (Anomia simplex), also known as Mermaid's Toenail and Saddle Oyster, is a bivalve with two different thin, translucent, irregular shaped, pearly valves: one curved, usually yellow, silver, whitish or orange, and the other one is flat and whitish with a hole at the apex.

It has a fleshy appendage (byssus) which passes through the hole to anchor itself upon rocks, seaweeds, or old shells. Consequently, usually only the upper valve washes ashore.

Jingle Shells are often attached to submerged objects so thickly that one grows on top of another so that oyster dredges will bring them up in quantity.

Size, Habitat and Range

  • Size: Up to 2 inches
  • Habitat: Shallow waters, beaches, oyster beds, and mollusk shells.
  • Range: Nova Scotia, Canada to Florida, Texas and the West Indies
Kitten's Paws Seashells (Plicatula, giblosa)

Kitten's Paws Seashells (Plicatula, giblosa)

16. Atlantic Kitten's Paw

Atlantic Kitten's Paw (Plicatula gibbosa) is related to oysters and is sometimes called Cat's Paw. Still, I prefer the former as they are tiny little seashells no bigger than a penny and too cute to be associated with the mighty hunter.

Their valves vary in color and are almost flat, but tough, with a bumpy texture and have an irregular triangular shape resembling their name. They typically attach themselves to rocks using the left valve, so it's more common for seashell hunters to find the right valve onshore.

Size, Habitat and Range

  • Size: Up to 1 inch
  • Habitat: Offshore in sandy substrate up to 300 ft (91m) depth
  • Range: From North Carolina to Florida, east to Louisiana and as far south as the West Indies
Tampa  Tellin Seashells (Tampaella, tampaensis)

Tampa Tellin Seashells (Tampaella, tampaensis)

17. Tampa Tellin

Tampa Tellin (Tampaella tampaensis) is colored opaque white (sometimes tinged pinkish-orange) with a shiny white interior. It has rounded, oblong-shaped valves with very thin concentric ridges on the exterior. The valve is fairly symmetrical from its somewhat pointed beak.

The valves are relatively thin and compressed. The hinge is not strong, and shells washed up on the beach are often broken.

In general, Tellin clamshells belong to a family which is often considered the aristocracy of bivalves. Of several hundred species, scores are found along both U.S. coasts, especially in the warmer waters of the Atlantic and Gulf coasts.

Some Tellins are rose-colored and attractive with banded patterns, very desirable to collectors, but most are white to creamy. There are plenty of photo samples on the internet for viewing more of the varieties.

Size, Habitat and Range

  • Size: Average 1/2 inch up to 4 inches
  • Habitat: Shallow sand and grassy inland bays and lagoons
  • Range: Florida to Panama and Texas
Speckled Tellin or Interrupted Tellin Seashells (Tellina, listeri)

Speckled Tellin or Interrupted Tellin Seashells (Tellina, listeri)

18. Speckled Tellin

Speckled Tellin (Tellina listeri) also known as Interrupted Tellin, has an exterior valve that is creamy-white with purplish-brown rays or speckling. The interior is white with the colors showing through. The shell is moderately thin, long and oval. The valve has strong concentric lines and a crease extending from the beak to the edge. It is not edible.

Size, Habitat and Range

  • Size: Up to 2 inches
  • Habitat: Moderately shallow water, but buries itself deeper in the mud and sand than most bivalves
  • Range: North Carolina to Florida and Brazil
Coquina Clam Seashells (Donax, variabilis)

Coquina Clam Seashells (Donax, variabilis)

19. Coquina Clams

Coquina Clams (Donax variabilis) are found in all colors and patterns of the rainbow. The colors can range from yellowish-brown to blue, lavender to green and even pink. Many are plaid. Their shells are asymmetrical from their pointed beak, slightly elongated and inflated.

These are little clams that create the activity you see at the tide line of the surf. With the aid of a fleshy foot, they dart about and can bury under the sand in a twinkling. Apparently, they are sensitive to light and rush to get back into darkness under the sand. They are great in soup, and crafters desire them for their beauty.

Size, Habitat and Range

  • Size: Up to 3/4 inches
  • Habitat: Sandy shallow subtitle zones
  • Range: Virginia to both coasts of Florida and Texas

I hope you enjoyed my photos and descriptions of those curious clams!

Sources

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Kathi Mirto