Euspira lewisii (Gould, 1847)

Common name(s): Lewis' moon snail, Moon snail

Synonyms:  Lunatia lewisii, Polinices lewisii
Phylum Mollusca
Class Gastropoda
Subclass Prosobranchia
Order Mesogastropoda
Suborder Taenioglossa
Family Naticidae
Euspira lewisii found on sandy bottom at 18 m depth in outer Bowmans Bay.  The animal's huge foot is extended and it is crawling rapidly to the left, as can be seen by the slime trail extending to the right.  The shell is almost entirely covered by the foot and mantle.  When moving the animal secretes copious mucus, strands of which are visible on the surface.  See photo below for the shell.  The animal above is 20 cm long.
(Photo by: Dave Cowles, July 2007)
Description:  Members of Family Naticidae have wide, globose shells with short coiled spires (total of 5-6 whorls) and a diameter nearly equal to the height, no siphonal notch, interior of the shell is not pearly (photo), there is a horny or calcified operculum.  The large body whorl comprises much of the shell mass.  The shells of Family Naticidae have an open umbilicus or the umbilicus is closed with an obvious callus. Euspira lewisii has an open umbilicus and a horny operculum (photo).  It can grow to 14 cm diameter.  There is a shiny callus on the inner lip of the aperture that spreads out widely on the body whorl and partly fills in the umbilicus (photo) so the umbilicus isn't more than 1/8 the diameter of the shell.  Color of shell cream, pinkish, beige, or yellow-brown.

How to Distinguish from Similar Species:Polinices draconis is a large subtidal species that does not have a large callus that partly covers the umbilicus, so the umbilicus is about 1/3 the diameter of the shell.  It is found mainly in California.  Euspira pallida (formerly Polinices pallidus) grows only to around 3 cm diameter and has only 4-5 whorls.  It may be whitish, grayish brown, or cream.

Geographical Range:  Ketchikan, Alaska to Baja California, Mexico

Depth Range:  Intertidal and subtidal to 50 m

Habitat:  Abundant on mud flats and silty sand, soft bottoms subtidally.

Biology/Natural History:  This snail, which is one of the largest to be found intertidally in the Northwest, is an active foraging predator on mud flats and sandy bottoms.  When the animal is fully expanded out of its shell it is so large that it covers almost the entire shell and looks as if it couldn't possibly fit into the shell.  Much of the expansion is due to the uptake of water, however, and if the animal is gently disturbed it will slowly release water from sinuses in the mantle and foot and contract into its shell, finally closing a horny operculum.  It does not usually stay inside the shell long because it cannot breathe.  It crawls across sandflats and mudflats with its huge foot partly extended in front of the shell like a snowplow, pushing through the sediments in search of clams.  It may burrow at least 10 cm into the sand.  Bivalve prey include Mya truncata,Tresus capax, Saxidomus gigantea, and Protothaca staminea clams but don't seem to seek out cockles Clinocardium nuttallii which are found in the same areas, probably because their shells are thicker.  The moon snail can bore about 1/2 mm per day.  Some clams are found with characteristic, "countersunk" drill holes through the shell made by the radula; while with others the snail seems to simply surround the clam with its enormous foot and wait until the clam suffocates enough to open up.  Predators on Euspira lewisii include the sunflower star Pycnopodia helianthoides.  It quickly withdraws its foot when it contacts Pycnopodia. Enteroctopus dofleini may be another predator, and the moon snails themselves may sometimes be cannibalistic.  Eggs are laid in a distinctive gelatinous coil or collar shaped as if it were formed around the top of a canning jar.  The egg mass is a firm gelatin with thousands of embedded eggs.  Sand is also embedded in the mass, giving it a sandy texture.  The coil is left on the sand. Eggs hatch into free-swimming, nonfeeding veliger larvae in midsummer.  Males are smaller than females, and females can live up to 14 years.

Shells from these snails are abundant in shell middens left by native Americans.  The species can become toxic if they consume toxic clams during a red tide.  They are also a favorite shell for large hermit crabs such as Pagurus armatus.



Dichotomous Keys:
  Flora and Fairbanks, 1966 (as Polinices lewisii)
  Kozloff 1987, 1996 (as Polinices lewisii)
  Smith and Carlton, 1975 (as Polinices lewisii)

General References:
  Brusca and Brusca, 1978 (as Polinices lewisii)
  Carefoot, 1977 (as Polinices lewisii)
  Harbo, 1997
  Harbo, 1999
  Hinton, 1987 (as Polinices lewisii)
  Johnson and Snook, 1955 (as Polinices lewisii)
  Kozloff, 1993 (as Polinices lewisii)
  McConnaughey and McConnaughey, 1985 (as Polinices lewisii)
  Morris, 1966 (as Polinices lewisii)
  Morris et al, 1980 (as Polinices lewisii)
  Niesen, 1994 (as Polinices lewisii)
  Niesen, 1997 (as Polinices lewisii)
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985 (as Polinices lewisii)
  Sept, 1999 (as Polinices lewisii)
  Snyderman, 1988 (as Polinices lewisii)

Scientific Articles:
Bernard, F.R., 1967.  Studies on the biology of the Naticid clam drill Polinices lewisi (Gould) (Gastropoda Prosobranchiata).  Technical report (Fisheries Research Board of Canada) no. 42

Page, Louise R., and Roberta V. K. Pedersen, 1998.  Transformation of Phytoplanktivorous Larvae into Predatory Carnivores during the Development of Polinices lewisii (Mollusca, Caenogastropoda).  Invertebrate Biology 117(3): 208-220

Peitso, E; Hui, E; Hartwick, B; and Bourne, N, 1994.   Predation by the naticid gastropod Polinices lewisii (Gould) on littleneck clams Protothaca staminea (Conrad) in British Columbia.  Canadian Journal of Zoology 72(2): 319-325


Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

We do not often see moon snails in the relatively exposed, rocky areas around Rosario but the individual below was found subtidally on silty sand just south of the station.

This is the same individual as above after being coaxed to close up inside its shell.  Note the horny operculum, and the large callus which partly covers the umbilicus.
The shell of this individual is about 9 cm in diameter.

This is what the shell itself looks like.


The shell in the photos below is a very small empty shell, 1.7 cm height and 1.8 cm width, trawled from 135 m depth by benthic sled in San Juan Channel, July 2018. Stacked (high depth-of-field) photos by Dave Cowles
Top view Aperture 1
aperture-umbilicus callus In the photo at left the porcellanous but not pearly inside of the shell can be seen, plus the callus on the columella that mostly obscures the umbilicus even at this very small size.

Authors and Editors of Page:
Dave Cowles (2007):  Created original page
Jonathan Cowles (2007):  Updated page with CSS