Biology Question #2164

Christine Scott, a female from Saltspring Island, BC asks on June 7, 2004,

My question is about the reproduction of the Moon Snail Polinices lewisii. Are the eggs laid within the sand/mucous collar, or are they sandwiched between two plies of egg collars? Are they visible? Do the egg collars that wash up on the beaches at low tide contain eggs?

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The answer

Peter Fankboner answered on July 3, 2004

In the Lewis Moon Snail, the eggs are contained within the jelly-like matrix forming the core of the sand collar.  To view the eggs, a small piece of the collar should be teased apart under a dissecting microscope in seawater using fine needles.  Whether egg collars which are found at low tide contain eggs depends upon whether there has been sufficient time for the eggs to have hatched prior to the collar's stranding.  The hatching time is for Polinices lewisii (Gould, 1847)) is about 1.5 months.

Christine Asks: By 'stranding', do you mean that the collar is in two plies and comes apart eventually as a natural course of events?

The egg case of the Lewis Moon Snail is produced as a single gelatinous ribbon which incorporates sand grains into its matrix as it is extruded from the snails aperture. The eggs number in the thousands and hatch into microscopic, butterfly-like veliger larvae which swim (via cilia) and feed in the plankton until they undergo a process called torsion and metamorphose into minute versions of moon snail adults. A stranded collar is a single ribbon unit.

- Are they becoming endangered?

Not that I'm aware of. But moon snails are often treated as pests because they compete with man for clams. When I worked years ago on cockles, I would wade into Pat Bay on Vancouver Island at low tide and look for the telltale trails made by Lewis Moon Snails as they moved through the sand looking for food. At the end of these sand trails I would normally find the maker, and picking it up would usually find it trying to bore through the shell of a cockle. I would remove the cockle and replace the snail back on the sand to look again. I could usually find a dozen cockles this way in less than 15 minutes.

The process by which moon snails take their food in interesting. They possess a button like process on the bottom of the anterior portion of the foot which secretes an enzyme which can dissolve the glue which holds the crystals of the prey's shell together. This button is placed against the umbo (the best meat is directly underneath) of the clam to cause the shell crystals of calcium carbonate to fall apart. Next the snails snout is placed against the eroded area to clean up the loose crystals. These are swallowed by the snail. This process is repeated until a hole in the shell becomes large enough to admit the snout for feeding on the soft tissues of the clam.

Hole drilled by moon snail

- Does the behaviour of beachcombers present any danger to the moon snail?

Beachcombers are normally interested in picking up empty shells, so they likely pose little danger to the local population of moon snails.

- Do people take live moon snails home to make snail chowder?

First Nation people, who will eat the foot of the Gumboot Chitin, won't give the Lewis Moon Snail more than a passing glance. I understand that east coast species of Polinices, however, are eaten in chowder, and are referred to as "sweetmeat."

Moon Snail, polinices lewisii

- Lastly, is Polinices lewisii the largest gastropod in the Pacific Northwest?

I can think of at least two British Columbia gastropod species which are larger than P. lewisii (5.5"): the Oregon Triton Fusitriton oregonensis (6") and the Pinto Abalone Haliotis kamtschatkana (6.5"). Arguably the largest gastropod species in the Pacific Northwest is the Red Abalone Haliotis rufescens (12") which ranges from Oregon to Baja. All three of the latter species can be found in the intertidal.

Peter Fankboner answered on May 10, 2005

Annette Olson asks: Does the egg case of Polinices lewisii have any predators?

Dr. Fankboner responds: I hit both the web and the literature on this question, and couldn't find any reference to predation on moon snail egg cases. This would make a nice project for a student to carry out under the controlled conditions of a marine holding tank. If I'm free to speculate here, I would suggest that the following organisms are potential predators on the egg cases: Olive snails, small crabs and other crustaceans, bottom feeding fishes, flat worms and ciliate protozoans. Ed Ricketts notes in "Between Pacific Tides" that there is an irony in the fact that the bivalves upon which adult moon snails normally prey may in turn filter-feed upon the free-swimming veliger larvae emerging from the moon snail egg case.

Peter Fankboner answered on May 24, 2006

Lesley Wolford asks: Have been looking up moon snails since seeing a few, and lots of sand collars last Tuesday on Cherry Point beach at very low tide. The Atlantic one was named Polinices duplicatus and the Pacific one Euspira lewisii However on your site, and others, I find it is called P. lewisii. How come? On one site I typed each one and nothing came up for either. It was P. lewisii on that site, but I tried out of curiosity.

Dr. Fankboner answers: I presume that the Cherry Point beach to which you refer in your query is located in North Carolina. As you can determine from the following, the taxonomy of the two species of moon snail in your question has recently undergone change. Neverita (=Polinices) duplicatus (Say, 1822) is an East Coast species of moon snail known by the common names of the "Atlantic Moon Shell" and the "Shark Eye Moon Snail." Specimens of the Atlantic Moon Shell may reach 2.5" in height. Euspira (=Polinices) lewisii (Gould 1847) or the Lewis Moon Snail is a Pacific Ocean species which has the distinction of being the largest moon snail extant (up to 5.5" in height).

To reduce confusion, it is acceptable to place a recently invalidated genus (with an equals sign) in parentheses between the valid genus and species names. Some genus names are lengthy, and once a genus has been spelled out in full in a paragraph, it may be subsequently abbreviated to its first letter (for example, Polinices becomes P.). Genus and species names are distinguished from other taxonomic names by writing them in italics, or if italics are not available, you may use underlining (instead of Euspira (=Polinices) lewisii (Gould 1847), you would write Euspira (=Polinices) lewisii (Gould 1847). The last name(s) of the species describer, followed by the date the species was described, is added in parentheses at the end of the species name.

Peter Fankboner answered on August 6, 2007

Reader Bruce Mouniere asks: What is the best time day or night  and where do you look  in the Washington Pacific North West area to find the lewis moon snail?

Peter Fankboner answers:

The best place I have found to collect them is Pat Bay on Vancouver Island, Canada.  Time of collection would depend upon time of tidal cycles (we have about two per day in B.C.), and the ideal time would be low low spring tide during the day near eel grass clumps where they can usually be found drilling their favorite prey, the heart cockle.  The last time I looked into this, you had to get permission from the first nations reserve at Pat Bay to collect, and you also have to have a collecting permit issued by Federal/Provincial fisheries.  Another possibility would be Crescent Beach at White Rock, BC, Canada where I have occasionally seen moon snail egg cases during field trips. [Editor: similar locations should yield lewis moon snails in Washington State.]

Richard Lyons, retired physician in Des Moines, WA answered on June 4, 2008

Peter Fankboner has provided fantastic answers to the above questions and I salute his accurate as well as inspiring responses.

Just to add some info about Washington State locations, we live in Des Moines WA just a few miles South of the Seattle airport. Today (June 4/08) along the beach just North of the Des Moines public fishing pier, we saw hundreds of the castings of the E. (P.) lewisii species all along the shore (as far as I could see in either direction) and also found a number of the live snails buried a number of inches below the surface of sandy mud along with artistically drilled access holes to the succulent offerings inside their cockles. A most amazing site because of the great numbers. I have seen them on a fairly low minus tide many times in muddy or even clean sand bottoms all around Puget Sound, Hood Canal, and the San Juan Islands and have often seen them crawling along partially burried in the sand as they feed when I have been scuba diving. Today, we picked some of them up to admire their robust shells and fleshy feet and then carefully placed them back on the sand where they dug back into their homes within about 3 or 4 minutes and disappeared as though nothing had ever happened.  Marvelous to behold!

Andrew Grebneff answered on September 18, 2008

Euspira lewisii was incorrectly placed in Polinices. It has been transferred to Euspira (=Lunatia). Lunatia is a junior synonym and should not be used; it is an available name but invalid. Polinices is an older name than Euspira, and is valid. However species belonging to Polinices are very different in shell characters to Euspira. Polinices should not be used in parentheses with Euspira; this would be the perogative of Lunatia.

Now, if anyone knows of any good live-gastropod collecting localities on Vancouver Island other than the Ogden Pt Breakwater, please reply below and the message will be forwarded to me.

Unfortunately I don't have a reference for either the placement of P. lewisii or the synonymization of Lunatia with Euspira. I do know that the latter happened before 1990.

However a glance is enough to show that P. lewisii is a Euspira; these have a satiny to dull surface with a wide-open umbilicus, and tend to be spheroidal and thinshelled for their size. Euspira has little or no sign of a funicle. Subsutural collabral wrinkles can occur. Polinices has a macrosculpture-free polished ovoid shell with a relatively thick lip and large (often completely filling the umbilicus) funicle, which often has a distinctive (to specific level) groove or pair if grooves.

Noelle in Puget Sound asks: answered on July 18, 2010

Actually, another question we are still trying to definitively answer for the Euspira lewisii here in Puget Sound: How MANY sand collars are individuals able to produce in a single year? Anyone out there studying this species? Seems this would be an relatively "easy" one to answer(?) THANK YOU!

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