Most seashells come from mollusks, a large group of marine animals, including clams, snails and oysters, which make shells as a protective covering. These shells are created from the outer surface of the animal and are made up mostly of calcium carbonate. A mollusk has the same shell for its entire life. After the animal dies, the shell remains. Ocean currents carry shells underwater before they often wind up on shore. While there are thousands of mollusk species, here is a small sample of some of the different types of shells.

Mollusks are invertebrates and are responsible for most shells that are found on the beach. There are more than 160,000 species estimated to make up the mollusk phylum. The seven classes are:

Gastropoda: single-shelled snails, whelks, cones

Bivalvia: two-shelled clams, cockles, scallops

Most seashells fall into the gastropoda and bivalvia categories. Shells can also come from echinoderms (sea stars, sand dollars, sea urchins) or crustaceans (crabs and lobsters).

A mollusk forms a shell as protection for its soft body. Unlike typical animal structures, seashells are made up of minerals instead of cells. The mollusk’s mantle tissue secretes calcium carbonate and protein to form the shell. The shell is attached to the mollusk, but is not actually a part of the body. Shells grow from the bottom up, and as the animal ages, the shell gets larger. When a mollusk dies, it discards its shell.

Seashells can be plain and smooth or adorned with spikes and ridges. Elaborate shells ward of predators, while sleeker mollusks can move quickly and without detection.

Mollusks can turn their shells different colors by eating a variety of colorful food.

Auger shells are whorled, narrow and elongated. The exterior can be smooth or ribbed. These shells range from 1 inch to almost 9 inches in length. The plate that seals the mouth of the shell is pointed on one end and rounded at the other. They are sand-dwelling carnivores found in warmer waters. There are about 20 species of auger that occupy North American waters.

The cockle family of shells is one of the largest and best-known of the bivalvia class. There are more than 200 species of cockle shells. These shells are strong, compact and heart-shaped. Some species of cockle have ribs, while others are smooth. The two shells that make up a cockle are completely symmetrical and equally sized. Cockle shells range from about 1 centimeter to 6 inches.

A conch is a marine snail. All 70 known species of conch shells inhabit tropical waters. The species found in North America range from 2 to 12 inches in length and are thick with an extended outer lip. Conchs are herbivores. Conch meat is harvested and consumed in Caribbean countries, while conch shells are coveted by collectors. This overharvesting has resulted in the decline of natural populations.

Nearly all 600 species of cone shells around the world have a similar distinct design: a conical shape, flat top and slit-like lip along its length. The shell’s exterior can be smooth or ornamented. They range in height from 1 inch to 8 inches. Cone shells are carnivorous and stun their prey with a venomous harpoon. Some have venom powerful enough to be lethal to humans.

Coquina shells are not much bigger than a dime. Because of their size, they are food for various sea life, including crabs and seabirds. Coquina are most often seen digging their way into the sand when a wave recedes. They can be a variety of colors and patterns. When empty and open, the hinged shells look like small butterflies.

These conical shells may be smooth or ribbed and round or narrow at the base. They can reach 4 inches in diameter. Limpets living in more active, wave areas have lower shell heights than those in calmer waters. Keyhole limpets have a hole in the apex of their shell that sets them apart. Approximately 35 species of limpets live in North American waters.

Also called shark eyes, these shells have whirled bodies that spiral inward toward “the eye.” Moon shells are carnivorous sand-dwellers. They can be found in sand or mud worldwide and are common finds along North American coasts. Moon shells vary in length from 1 inch to 5 inches. They are usually round and smooth with short spires.

Murex shells are known for their variety of ornamentation and sculpture. While some are colorful, the majority of murex shells are plainly colored. They live in habitats from the tropics to the polar regions, and feed on other mollusks. There are about 140 species of murex in North American waters. They range from about 1 inch to 10 inches.

Olive shells come in various patterns and have a smooth, shiny surface. These shells resemble a long, pointed tube with small spirals at the top. There are 25 species of olive shells in North American waters. Olive shells can vary from 1 inch to 5 inches in length. A fresh olive shell can be patterned with hundreds of small triangles and abstract designs.

Scallops can swim by opening and closing their shells, propelling themselves rapidly in a zigzag direction. Most scallops are tropical, but a few live in polar waters. Scallop shells vary in color and texture, but the two valves of the shell are usually fan-shaped. The lower valve is usually lighter in color and less sculptured than the upper valve. Scallop shells range in size from 1 inch to 6 inches.

Also called screw shells, turret shells resemble long, slender screws. They are similar to auger shells, but their shape is variable, and the shells are thin and rough. They have a rounded mouth, a tall spire and numerous convex whorls. Turret shells range in size from 1 inch to 5 inches. These snails are sand-dwelling carnivores that live in warmer waters. There are 17 species of turret shells in North American waters.

Whelk shells are commonly mistaken as conch shells as their appearance is similar. They have a strong spiral shape and either a smooth or sculpturing surface. About 200 species of whelks live in waters from the arctic to the tropics. Whelks are much more common than conchs along the northern East Coast. Tropical species tend to have thicker shells. They range in size from 1 inch to 8 inches.

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