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Snails in Barnegat Bay





Radula Details



Phylum: Mollusca  Mollusks     Class: Gastropoda Gastropods

Gastropoda - Latin meaning: gaster=stomach podus=foot

Marine Snails

Worldwide, there are over 40,000 recognized species of snails consisting mostly of marine snails of which, several species inhabit Barnegat Bay.

Snails are univalves, meaning they have one shell (valve) to which they can retract their whole body into when threatened.

They can be algae eaters (algivorous), predators and scavengers

Projecting out in front of the snail are two tentacle which are used for sight. Another set are used for touch.  Below these tentacle is the mouth. 

The snail crawls and climbs with its foot. A spiral shell protects its internal organs, including the stomach, the digestive tract, the heart and blood vessels, the kidneys, and the gonads.

A thin membrane, called the mantle, protects these organs and also secretes the shell.

When a snail withdraws into its shell, a small disk called an operculum seals off the entrance.

While the shell is the snails primary means of protection, the ability to adhere to a surface and  in some species, production of noxious compounds also offer protection from predators.

Most snails have thousands of microscopic tooth-like structures located on a tongue-like ribbon called a radula. The radula works like a file, ripping the food into small pieces


   Mud Dog Whelk   Ilyassoma obsoleta       also called Eastern Mud Snail

The mud dog whelk (also called eastern mud nassa, eastern mud snail, mud basket shell, common mud snail) is about ¾ of an inch in length.

It has a chalky white shell, but is covered by a dark brown to red-brown periostracum.  It has 6 whirls and an operculum.

Theses snails form large clusters that tend to be divided into age groups. They are always found in large numbers, sometimes in the hundreds of thousands.

Mud snails are scavengers and can be attracted to bait or dead fish.

The snails leave a mucous trail as they glide along the bottom. The mucous is a chemical trail marker. Other snails will find the trail and follow it. The only time this does not seem to hold true is if one of the snails is sick or injured. The other snails will quickly abandon the unfortunate snail.

Fun Fact - the empty shells of mud snails often become a new home for hermit crabs.

Moon Snails

Moon snails are found in all seas around the world and throughout Barnegat Bay. They are carnivorous predators who's major food source is calms and other shellfish (even other moon snails).

Moon snails have a large grey to tan shell (adults about 3 to 4 inches) with a large foot. 

The snail pumps water into its mantle and foot to increase its mass by 3 to 4 times the size of its shell <see image to right>

They use this foot to travel along or burrow into the sandy or muddy bay bottom in search of prey.

When threatened, they pump out the water to retract their entire body into the shell  and seal the entrance with the operculum

When a hunting moon snail finds its prey (usually a clam) it surrounds it with its large foot. It then proceeds to use its radula to drill a hole in its victim's shell.

As the radula scrapes away pieces of the shell, the process is assisted by the secretion of acidic enzymes to soften and dissolve the calcium carbonate of the calm's shell.

Once the hole is completed, the moon snail inserts its tubular mouth (proboscis) into the opening to ingest the contents of its victim leaving an empty shell with a perfectly round hole as seen in the image to the right.

Fun Fact - Moon snails are nocturnal.  They do most of their hunting at night and spend the day buried in the sand or mud of the bay bottom.

Learn more about moon snails  <click here>

Moon Snails in Barnegat Bay

There are primarily two species of moon snails that inhabit Barnegat Bay:

The Northern Moon Snail (Lunatia heros)

The Atlantic Moon Snail (Polinices duplicatus)

Both of these species are have similar anatomy and behavior as discussed in the above section "Moon Snails".  The sections below will focus on the differences


Northern Moon Snail     Euspira heros

Northern moon snails grow up to 4 - 5 inches high and almost equally as wide (almost round). The shell is smooth and  grayish-white to brownish-gray in color.

One feature that is unique to the northern moon snail is umbilicus.

As a snail grow, its shells revolve around a central axis, or columella.  

In young snails this growth results in a hollow tube running through the center of the shell called an umbilicus.  Normally this "navel" is filled in with calcium as the animal grows. In the northern moon snail this umbilicus is not filled in.  


 Atlantic Moon Snail     Polinices duplicatus

Atlantic moon snail or "Shark's Eye" has a bluish gray-brown color with a  distinctive dark “eye” at the tip of the spire as shown in the image to the right     

<click on any image to enlarge>

They grow to about 3 inches in diameter.

The Atlantic moon snail, like most other moon snails has its umbilicus filled in or partially filled in as the shell grows.








 The above shows detail of the moon snail's shell and umbilicus <click on image to enlarge>

Atlantic Oyster Drill       Urosalpinx cinerea

The Atlantic oyster drill is a carnivorous snail that makes its home in Barnegat Bay.  They grow to just over an inch long.

Oyster drills feed mainly on bivalve mollusks, especially oysters. Muscles have relatively thin shells and can be penetrated more easily than clams, barnacles and other snails. Oyster drills themselves can become a victim of their own species.

When a drill finds a victim it grips onto the shell tightly with its foot and begins the drilling process. This involves not only scraping with the radula, but also an application of calcium-dissolving acid to help soften the shell and make the drilling easier.

This process is similar to moon snail predation but the size of the hole in the victim's shell is much smaller, more the size of a pinhole.

Atlantic Slipper Shell        Crepidula fornicata

The Atlantic slipper shell is a marine snail that grows to approximately 1 to 2.5 inches in length.

They usually sit in stacks (one on top of another) on a hard substrate, e.g., the shell of another mollusk, a rock or < in this example, a bottle >.  When small, slipper shells are male and live on top of females, often with several males next to or on top of each other. When the female dies, the bottom, largest, male in the stack changes to female

This sea snail has an arched, rounded shell. (upper image). On the inside of the shell (lower image) there is a  "deck" which causes the shell to resemble a boat or a slipper.

They are active suspension feeders, generating a water current through the mantle cavity using cillia and trapping food particles on a mucous sheet lying across the front surface of the gill filament.


            <click here> for more images and information

<click on image to enlarge>


Jacksonville Shells -