Six-year-old Luke Callihan, of Pennington, collects shells on the beach in Brigantine, Sunday, July 2, 2017.
By Lori M. Nichols | For NJ.com
Originally published Aug. 2, 2018
Maybe collecting shells is a favorite pastime of yours, but you don't know which is a moon snail and which is a mud snail. Or, you're walking along the beach, and something shiny catches your eye, but what is it?
Well, look no further: Here's a guide to some of the most common shells found on New Jersey beaches, and answers to your head-scratching questions like where the holes in a clam shell came from? And what is a mermaid's purse, exactly?
Lori M. Nichols | For NJ.com
1. Ever wonder why you see so many shells with a single hole in them?
That's the result of a hungry moon snail.
Moon snails release an acid onto the shells of clams and other snails to soften the shell, then drill a borehole into the shell with its radula (kind of like a toothed tongue) and feed off the meat of the "victim".
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2. What was growing on that shell?
Barnacles attach themselves to a hard substrate, such as shells, rocks and pilings.
Note the pattern left behind after the barnacle is no longer attached.
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3. Same shell, different colors
That black bay scallop shell you have in your hand isn't naturally that color. And neither is that brown Atlantic surf-clam.
Shells stained brown or orange got that way from iron oxide forming along the microscopic cavities of dead mollusks. Up to 30 percent of shells on any New Jersey beach will be brown.
Black-stained shells have been buried in the mud for hundreds, if not thousands, of years. They make their way to the beach after being dug up by dredging. With so many beach replenishment projects along the Jersey Shore, you're bound to find a lot of black-stained scallop, oyster and clam shells.
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4. Not so "boring" designs
If you find a shell with a ton of holes in it, you might think it resembles a sponge.
Well, that's because those holes were made by a boring sponge, drilling holes into shells for their calcium.
The designs left on shells as a result can be pretty and quite interesting.
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5. Who, or what, carved the letter "C" in this shell?
Polychaetes, also known as a bristle worms, leave snaking groove marks in shells. Sometimes the grooves are short, as pictured here, but can be much longer.
There are more than 10,000 species of polychaetes, living in all of the earth's oceans. On each segment of their body, there is a pair of fleshy protrusions that bear bristles, called chaetae.
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6. Upside down or downside up?
More than 75 percent of the time, clam shells will come to rest on open-ocean beaches concave side down (pictured at left). But why?
Hydrodynamics. The shell is more stable in this position, as it allows the waves to wash over it, instead of knocking it around.
However, there are some beaches where shells come to rest concave side up. Typically this happens because an offshore bar breaks the strength of waves.
This "rule" also applies to similarly shaped shells, such as scallops, arks and oysters.
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7. Living in borrowed shells
Hermit crabs are crustaceans with soft, exposed abdomens, which leaves them vulnerable to predators.
So how do they protect themselves?
They look for abandoned shells, and once they find one that fits, they move in and carry their new home with them wherever they go. Until they outgrow their borrowed shell and find a new one, that is.
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8. Sand collars
Sand collars are the egg masses of moon snails. They are made of sand grains held together by a jelly-like, mucousy substance; the eggs are located within this mixture.
They get their name from their appearance, for when found intact, they look like an old-fashioned detachable shirt collar.
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9. When is a crab not actually a crab?
When we're talking about horseshoe crabs.
While they may resemble crustaceans, they're actually closely related to arachnids (yup -- spiders, scorpions and ticks).
They are often referred to as "living fossils," as they existed more than 445 million years ago -- 200 million years before dinosaurs existed.
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10. Sand crabs
By the name of the sand crab, you can likely guess where it lives: in the sand. But these guys do much more than take up space on our beaches; they actually help clean it.
Sand crabs ingest toxins, including domoic acid -- a naturally occurring toxin produced by microscopic algae, which is poisonous to animals higher up in the food chain, including humans.
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11. Mermaid's purse, or devil's pocketbook
You might come across one of these on the beach and think it's just another type of seaweed.
But it's actually the egg case of a skate, a fish that resembles a stingray (they're actually part of the same family).
If you find a fresh, unhatched pod, you can hold a light underneath it (try the LED light on your cell phone) to see the fish embryo inside.
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Wondering what's in your bucket?
Here's our guide to the shells you find on the Jersey beaches, from blue mussels to variable coquina.
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Knobbed whelk
The knobbed whelk is the official state shell of New Jersey.
Knobs -- some more pronounced than others -- form around the spire, giving it its name.
Size: 100-240 mm; common, although uncommon to find whole, unbroken shells.
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Channeled whelk
The channeled whelk has a pear-shaped shell with raised spires. Less damaged shells show "beads" lining the spires.
Size: 100-215 mm; common, although uncommon to find whole, unbroken shells.
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Common slipper shell or oyster-pest
The common slipper shell gets its name from its appearance: it looks like a slipper.
These animals are often found in chains of up to 12, attached to mussels or oysters. They start out as males and turn into females as they grow larger.
Size: 20-50 mm; very common.
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Eastern white slippersnail
The eastern white slippersnail has a convex, or sometimes flat, shell due to where the animal lives: inside the shells of snails and slugs, feeding off the waste from the hermit crabs often living inside the shell as well.
Size: 12-30 mm; very common.
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Blood ark
The blood ark has a somewhat circular shell with visible ribs (those lines extending from the top to bottom).
It gets its name from having red blood, noting the presence of hemoglobin, which makes it unlike most mollusks.
Size: 25-75 mm; very common.
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Transverse ark
The transverse ark has a white shell (it may be stained a darker color) with ribs radiating from the top.
Size: 13-38 mm; common.
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Ponderous ark
The ponderous ark has a shell with a high arch and squared-off, trapezoid-like shape. From the side, it almost looks like a wave crashing along the shoreline. It's heavy for its size.
The photo in the upper right shows its teeth.
Size: up to 60 mm; common, but usually as a fossil in New Jersey.
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Blue Mussel
The outside of the blue mussel shell is dark blue or black in color; the inside is often a shimmery white with dark purple borders.
Both halves of this bivalve are often found intact on beaches near inlets.
Size: 40-105 mm; very common.
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Ribbed mussel
The ribbed mussel has a somewhat thin, but strong, fan-shaped shell with noticeable ribs.
The inside of the shell is pearly gray.
Size: 60-100 mm; very common.
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Cayenne keyhole limpet
The Cayenne keyhole limpet is shaped like a cone, with a small hole at the top, called the keyhole.
This limpet lives in inlets and offshore waters and is occasionally found washed up on ocean beaches.
Size: 15-50 mm; common.
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Atlantic surf clam
One of the most commonly found shells on New Jersey beaches, and easily recognizable by its large size and oval to triangular shape.
Canned clams typically contain the meat from this mollusk.
Size: up to 225 mm; very common.
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Northern quahog
The northern quahog has a thick, heavy shell, with highly visible ridges.
You'll find these in your local fish market, labeled as littlenecks, topnecks and cherrystones, depending on their size.
Size: up to 150 mm; very common.
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Stout tagelus
The shell of the stout tagelus is rectangular or oval in shape, usually off-white in color.
Size: up to 118 mm; common.
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Variable coquina
These are the little clams you often see burrowing back into the sand in large groups after a wave crashes ashore.
Coquinas come in various colors, from almost white, yellow, pink, orange, red, purple, to brownish and blueish, and some have darker "rays" on the inside of the shell.
Size: 13-20 mm; very common.
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False angelwing or American piddock
The false angelwing gets its name from its appearance: when both shells of this bivalve are intact, the pattern of ridges and ribs make them look like angel wings.
Size: 25-70 mm; common.
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American mud snail or mud dog whelk
The American mud snail has a small, chalky white shell that is often discolored to a dark brown color due to its habitat, in muddy, intertidal areas and inlets.
Size: 18-25 mm; very common.
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Threeline mudsnail
The shell of the threeline mudsnail has a spindle shape, as well as distinct lines and ribs that give a bead-like texture.
Size: up to 20 mm; very common.
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Bruised nassa
The bruised nassa is a small shell shaped like a cone, with six or seven whorls.
Size: 10-20 mm.
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Eastern auger
The eastern auger is shaped like a unicorn horn, and is often pale gray or tan in color.
It only appears on the shores of New Jersey as a fossil, but commonly found from Maryland to Brazil.
Size: up to 57 mm; uncommon in New Jersey
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Bay scallop
The bay scallop has a fan-shaped shell with approximately 20 ribs, its natural color being more of a dark red.
Why is a bay scallop shell found on oceanside beaches? Dredging and beach replenishment are among the most common reasons.
Size: up to 95 mm; very common.
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Sea scallop
The sea scallop has a large, flat, fan-shaped shell.
The inside of the shell is glossy white with a muscular scar where the scallop was attached.
Size: 70-230 mm; typically found on New Jersey beaches after deep sea fisheries "drop" sea scallops close to shore.
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Common jingle shell
The common jingle shell gets its name from the sound it makes: just pick up a few and shake them in your hand to hear them jingle!
This shell is very thin and brittle; the shiny shell often has a hole in the middle once its washed up onshore.
Size: 25-50 mm; very common.
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Atlantic razor clam or Atlantic jackknife
This clam is long and narrow with squared-off ends and has a slight curve in its shape.
Size: 100-200 mm; common.
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Atlantic razor
The shell of the Atlantic razor is smooth, oblong and rounded at the ends. The shell is thin and fragile, with three light-colored "rays."
Size: 35-65 mm; very common.
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Shark eye
The shark eye is a type of moon snail, and has a dark "eye" at the tip of the spire.
The shark eye is commonly confused with the northern moonsnail: the shark eye has a patch of shell on the bottom which covers the hole in the center of the shell; the northern moonsnail's hole is not covered.
Size: 25-98 mm; very common.
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Northern moonsnail
The northern moonsnail can easily be differentiated from the similar shark eye by the uncovered hole at the center of the shell; the shark eye has a patch of shell covering the hole.
Size: 50-120 mm; very common.
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Eastern oyster
The upper shell of the eastern oyster is thick and highly arched, and the lower shell is smoother and flat.
This mollusk is highly important to the environment: just one oyster can filter more than 50 gallons of water in 24 hours.
Size: 50-200 mm; very common.
Lori M. Nichols | For NJ.com
Cross-hatched lucine
The cross-hatched lucine has a circular-shaped shell and a distinct chevron-like pattern in its grooves.
Size: up to 25 mm.
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Shells found along the Jersey Shore.
The shells in this article were found on various beaches in New Jersey by the author. The identifications were made by the author using several publications, both in print and online, and were then verified by Paul Callomon, collection manager, Malacology, Invertebrate Paleontology and General Invertebrates, at the Academy of Natural Sciences of Drexel University in Philadelphia.
Lori M. Nichols may be reached at lnichols@njadvancemedia.com. Follow her on Twitter @photoglori. Find NJ.com on Facebook.
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