For the past five years or so, a local dive group in the area called Mid-Coast Maine Aqua-Nuts have been compiling a photo database of marine life of Penobscot Bay. One of the more unique inhabitants of the bay is also one its more common residents.

It is the moon snail (Euspira heros), a gastropod commonly found from the Gulf of St. Lawrence to North Carolina. The idea that it is considered very common should not detract from its specialness or "cool" factor. This is because the moon snail just looks cool and collected and competent as it goes about its business chugging along on the mud and sand.

Euspira is the genus of medium-sized sea snails, the marine gastropod mollusks in the family Naticidae. First identified and classified by Louis Agassiz back in the 1830s, this group is thought to have originated in the late Triassic or early Jurassic period, nearly 200 million years ago.

Fossil records of them stretch from the Triassic to the Quaternary and are found in marine strata throughout the world. There are about 25 extinct species. The Germans call them Nördliche Mondschnecke.

The moon snails of Penobscot Bay tend to be big and distinctive; they can grow 5 inches or more, and are always exciting when you come upon one while diving. The shell is thick and round with five convex whorls. Empty shells tend to be a nice find while walking along the beach and are quite collectible.

The moon snail's habitat is usually on mud and sand in depths ranging from intertidal to over 1,200 feet. On one particular dive on the ocean side of the Rockland Breakwater, we came across so many that I thought of the Cat Stevens song “I’m Being Followed by a Moon Snail.”

I know, it should be moon shadow … but that song sure stuck in my head. We must have seen almost a dozen that day. There is a stretch of sandy bottom off Penobscot Park, the oceanfront site in Lincolnville that used to be owned by Point Lookout, and is now in transition to town stewardship. Just about every time we dive there, we come across moon snails galloping across the sand.

OK, maybe not a gallop, but they do move along at a decent clip. The foot and mantle have hollow gaps, or sinuses, that can greatly expand when water is pumped into them. It expands out from the shell and forms a plow-like appendage which they utilize to push themselves forward across the mud or sand surface. That foot can also quickly contract, especially when disturbed.

Moon snails tend to motor along with this locomotion when they are ready to feed … and a hungry moon snail is a mollusk on a mission. They are often seen plowing along the sand searching for prey. Considered to be voracious feeders, they are predatory rather than filter feeders, grazers or scavengers. They are thought to eat a meal every four days.

What do they eat? Moon snails tend to feed on herring eggs, clams and other shelled mollusks such as periwinkle snails and dog whelks. If need be, they will also feed on each other. Yes, they are cannibals.

Moon snails hunt by chemoreception, primarily with their senses of taste (gustation) and smell (olfaction). They sniff out chemical stimuli in their environment and, with their big foot, move into position and envelope the prey.

The next move is to drag the victim deeper into the sand. The moon snail then bores a hole through the shell with its radula, a kind of tongue with seven rows of sharp teeth! This easily identifiable shell hole is countersunk in appearance with beveled edges.

A gland on the moon snail proboscis then secretes enzymes and even hydrochloric acid into the shell. This acid secretion helps break down the clam or gastropod’s tissues, which are then rasped and sucked out, usually over a day or so. They are not in any hurry.

The hole size varies according to the species and is the signature of a moon snail feast. The next time you pick up shells along the beach and see these holes, you will know a moon snail has struck.

They have few predators, other than their own kind. If they get stranded by the tide, a seagull might try and make a meal of them. Moon snails then bury themselves into the sand with their large foot and await the next tide. A large sea star might occasionally try to eat one, but moon snails use that darn radula of theirs to saw away at the sea star’s tube feet and avoid becoming its meal.

Moon snails are one of the best-known invertebrates in the sandy intertidal zone here in New England. During winter, they move to deeper water and then return near shore in summer, during their breeding season. Males and females are separate; females tend to be larger with thinner shells than males. Their egg masses are equally notable.

During breeding season, the female lays a large mass of eggs stiffened with sand and mucus. These eggs are enjoyed by green sea urchins and some gastropods. This egg ribbon molds itself around the globular shell into the shape of a collar, oftentimes around 6 inches in diameter.

When the snail moves from it, these objects remain, known by their common name: sand collars. Pliant underwater, they turn brittle when dry. Sand collars often tend to wash up on beaches.

In the sand, the eggs hatch into planktonic veliger larvae, or the second larval stage. Soon they are released into the water. They are herbivores at this stage, existing mostly on diatoms and sea lettuce. It will not take long before they are grown and carnivorous …and chugging along the bottom looking for their next meal.

They were part of the Native American diet, but because moon snails feed on clams, some suggest caution today in eating them. It is thought they might accumulate poisons that could cause paralytic shellfish poisoning.

But they are popular in Korean cuisine. South Koreans make a small dish called golbaengi muchim, or moon snail salad. It is a mix of snails and vegetables, usually made with a red, spicy sauce and served with boiled somyeon, or wheat noodles.

South Koreans tend to eat it anju, served and eaten with alcoholic drinks. Sold in pojangmacha, or street stalls, Koreans consider it a casual kind of food, often served in small dishes. The moon snail, casual and common … interesting descriptors for a friendly-looking marine mollusk that is anything but.

Charles Lagerbom teaches AP US History at Belfast Area High School and lives in Northport. He can be contacted at He is author of "Whaling in Maine" available through