Euspira lewisii

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Geographic Range

Lewis's Moon Snail, Euspira lewisii, ocupies the Pacific Ocean coast, from Vancouver Island (British Columbia) to Isla San Geronimo (Baha California, Mexico). (Morris, et al., 1983)


Moon snails are inhabitants of soft sand or mud along the Pacific coast in protected bays, low intertidal areas, in the substratum off the coast to a depth of about 150 m. More snails are at the surface at night than during the day. They are found at the surface after heavy rains, but remain buried in cold weather. (Morris, et al, 1983)

Physical Description

Shell size up to 130 mm in diameter, or approximately 5 inches, although though usually 4 inches or less due to picking. A fully expanded animal is several times larger than its shell, which almost completely covers the body. Shell shape is globe-like, with shallow groove at the shoulder of whorls; columella with a calcereous callus reaching to edge of deep umbilicus. Shell color is yellowish with thin brown periostracum; the horny door (operculum) common to snails is dark brown. The snails plough forward with a foot just below the surface of the sand. When extended, the foot can measure over 12 inches in diameter. It is heavily ciliated, has mucus glands, and is very effective for moving over a shifting bottom. The mucus foot can fold into a grasping organ to hold prey. The foot also can be drawn inside the shell by an aquiferous system, but the snail cannot stay inside the shell for long periods of time because it cannot breathe. Life expectancy of this snail is estimated to be several years. (Morris et al., 1983; Ricketts & Calvin, 1962; Anonymous, 2000; J. Kirkhart, personal communication)

  • Average mass
    435 g
    15.33 oz


Males are smaller than females and their shells are slightly thicker. They begin to mate when they reach a shell length of 55 mm. Eggs are laid in a broad, rubbery "sand collar" about 15 cm diameter which forms around the shell and foot. This collar holds a layer of eggs (eggs are 250 micrometers in diameter) which is then deposited by ocean waves on the beach. The mucus collar is coated by layers of sand held together by the mucus. Moon snails lay eggs in shallow water in spring and summer, and eggs hatch in midsummer. A half-million or so larvae swim around inside the sand collar for several weeks until being released by disintegration of the collar. Young snails feed on diatoms, and on green seaweed called Ulva, at 10-12 m depth for five to six months. Afterwards, they begin to hunt animal prey in the substratum. They do not venture into shallower water until their shell lengths reach about 30 mm. (Morris, et al, 1983; Buchbaum & Milne, 1962; Shaefer, 1997)


Snails are usually found partially buried so that part of the shell is visible above sand, through which they plow easily. They normally avoid each other, but a feeding snail will attract other snails. (Morris, et al, 1983)

Food Habits

The moon snail's method of obtaining food is varied. They feed mostly on clams, mussels, or other mollusks. Moon snails usually clamp the foot around clam shells and proceed with drilling a hole with their radula, which is a long, ribbon-like tongue containing thousands of teeth (denticles) that project from the mouth opening. It is suspected that the foot smothers its victims to make their job easier. Studies indicate there is an enzyme secretion of carbonic anhydrase that has a softening effect on mollusk shells to aid in drilling. Food is extracted by sucking the foot over the hole, or by sucking through the siphon of a clam. Young snails feed on diatoms, and on green seaweed called Ulva, at 10-12 m depth for five to six months. Afterwards, they begin to hunt animal prey in the substratum. They do not venture into shallower water until their shell lengths reach about 30 mm. (Morris, et al, 1983; Buchbaum & Milne, 1962; Shaefer, 1997; Ricketts & Calvin, 1962; Anonymous, 2000)

Economic Importance for Humans: Positive

They are eaten by humans and other animals. (Morris, et al, 1983)

Economic Importance for Humans: Negative

Even though moon snails feed on clams, there has been no impact on littleneck clam farming. (B. Hartwick, personal communication)

Conservation Status

California Fish and Game regulations (1979) have set limits on the amount of moon snails taken, and none can be taken north of the Golden Gate Bridge (in San Francisco). The small crab, Opisthopus transversus, is sometimes found as a commensal of the snail, and hermit crabs are known to inhabit the empty shells. (Morris, et al, 1983)


Dianne Hoehing (author), Fresno City College, Shirley Porteous-Gafford (editor), Fresno City College.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.


Anonymous, 2000. ""Snail," Microsoft® Encarta® Online Encyclopedia 2000" (On-line). Accessed Oct. 26, 2000 at

Buchbaum, R., L. Milne. 1962. The Lower Animals, Living Invertebrates of the World. Doubleday & Co., Inc..

Morris, R., D. Abbott, E. Haderlie. 1983. Intertidal Invertibrates of California. Stanford, California: Stanford University Press.

Rickets, E., J. Calvin, J. Hedgpeth. 1992. Between Pacific Tides, Fifth Edition. Stanford, California: Stanford University Press.

Schaefer, J. 1997. "The Moon Snail" (On-line). Accessed Nov. 14, 2000 at