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Helisoma anceps

What do they look like?

Adult size of two-ridge rams-horn snails varies from 8 mm to 16 mm in diameter. Color varies, but may be tan to white. The shell is coiled to the left, and is thick and round. There are ridges on both sides of the shell, which gives its common name of "two-ridge". The foot, which is the portion of the body that the snail moves along on, is wide, rounded, and may have tiny white dots on it. This species has a single pair of tentacles with eye spots at the base. The tentacles are long and slender. The soft parts of the snail appear reddish, due to its blood. (Burch and Jung, 1992; Burch, 1989)

Where do they live?

The two-ridge rams-horn snail, Helisoma anceps, is found throughout North America. This species ranges from as far north in Canada as James and Hudson Bays, west to the Northwest Territories, Alberta, and Oregon, and south through Mexico. Its eastern range includes the Atlantic drainages of the United States. ("Helisoma anceps", 2003; Burch and Jung, 1992)

What kind of habitat do they need?

Two-ridge rams-horn snails live in permanent water bodies and are found among vegetation. In Canada, these snails are more frequently found in lakes than in rivers or creeks, but in other areas are found in both equally. This species is also found in substances such as peat, sand, and decaying matter. In a Northern Michigan lake, these snails lived in depths ranging from 0.5 to 9 m, but were mainly found at 6 m depths. As with other freshwater snails, they may move up and down in the water in response to food and water temperatures. (Burch and Jung, 1992; Laman, et al., 1984; Pip, 1987)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • Range depth
    6 (high) m
    19.69 (high) ft

How do they grow?

In general, these snails lay eggs in masses that protect them and help development. The time it takes for these snails to develop likely depends on temperature. Two-ridge rams-horn snails are considered to be adults when a ridge on their shell thickens. (Burch and Jung, 1992; Burch, 1989; Geraerts and Joosse, 1984)

How do they reproduce?

Two-ridge rams-horn snails are hermaphroditic, meaning that each individual has both male and female reproductive parts. They likely reproduce in the spring and summer. Although there is little information available about the mating behavior for this snail species, there is some information for related species. In these related snail species, they will begin mating when they encounter other snails, or may be more likely to mate when temperatures increase. (Burch and Jung, 1992; Geraerts and Joosse, 1984)

After mating, egg masses are attached to surfaces such as rocks, stones, or aquatic plants. About 20 to 30 eggs are in each mass. Less eggs tend to be produced when the population size grows too large. Females reproduce more with more and better food. (Geraerts and Joosse, 1984)

The egg masses produced by the parents provide a safe environment for the eggs to develop, away from predators and other threats. After they lay the eggs however, the snails leave and give no more parental care. (Geraerts and Joosse, 1984)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
    • protecting

How long do they live?

Two-ridge rams-horn snails likely live two to three years. (Burch and Jung, 1992; Zimmerman, et al., 2011)

  • Typical lifespan
    Status: wild
    2 to 3 years

How do they behave?

Two-ridge rams-horn snails tend to stay in one place most of their lives. In one study, snails that were released in to the water moved 1.6 m within 48 hours. These snails may move to look for food, which they can detect chemically. (Boss, et al., 1984)

Home Range

These snails typically stay in the same general area, maybe moving a few meters at the most. (Boss, et al., 1984)

How do they communicate with each other?

These snails have a centralized nervous system. They also have eye spots at the base of its tentacles, which can detect light. They can detect chemicals to find food. (Burch and Jung, 1992; Burch, 1989)

What do they eat?

Two-ridge rams-horn snails eat algae, bacteria, and protists, using its tooth-covered feeding structure called the radula. Chemical detection may be used to find food. This species prefers periphyton, a mixture of algae and other bacteria. (Burch and Jung, 1992; Burch, 1989; Weber and Lodge, 1990)

  • Plant Foods
  • algae

What eats them and how do they avoid being eaten?

Predators of these snails include the ribbon leech, Nephelopsis obscura, crayfish, fish and birds. Crayfish are such significant predators that snails are often not found in areas where crayfish are present. (Brown and Strouse, 1988; Dillon, et al., 2006; Weber and Lodge, 1990)

What roles do they have in the ecosystem?

Two-ridge rams-horn snails feed on algae. These snails are preyed upon by crayfish and other predators. Freshwater snails are often hosts for parasitic worms called trematodes. One of these parasitic trematodes is Halipegus occidualis. Two-ridge rams-horn snails are also host to the parasitic nematode worm Daubaylia potomaca. (Esch, et al., 1997; Zimmerman, et al., 2011; Esch, et al., 1997; Zimmerman, et al., 2011)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

These snails do not cause any problems for humans.

How do they interact with us?

Two-ridge rams-horn snails do not have any positive effects on humans.

Are they endangered?

Two-ridge rams-horn snails are not an endangered species.


Renee Mulcrone (author), Special Projects, Angela Miner (editor), Animal Diversity Web Staff.


2003. "Helisoma anceps" (On-line). Encyclopedia of Life. Accessed July 02, 2013 at

Boss, N., T. Laman, H. Blankespoor. 1984. Dispersal movements of four species of pulmonate and operculate snails in Douglas Lake, Michigan. The Nautilus, 98/2: 80-83.

Brown, K., B. Strouse. 1988. Relative vulnerability of six freshwater gastropods to the leech Nephelopsis obscura (Verrill). Freshwater Biology, 19: 157-165.

Burch, J. 1989. Freshwater snails of North America. Hamburg, Michigan: Malacological Publications.

Burch, J., Y. Jung. 1992. Freshwater Snails of the University of Michigan Biological Station Area. Walkerana, 6/15: 1-218.

Cummins, K., G. Lauff. 1969. The influence of substrate particle size on the microdistribution of stream macrobenthos. Hydrobiologia, 34: 145-181.

Dillon, R., B. Watson, T. Stewart, W. Reeves. 2006. "Helisoma anceps (Say 1817)" (On-line). The freshwater gastropods of North America. Accessed July 02, 2013 at

Esch, G., E. Wetzel, D. Zelmer, A. Schotthoefer. 1997. Long-term changes in parasite population and community structure: A case history. American Midland Naturalist, 137: 369-387.

Fernandez, J., G. Esch. 1991. The component community structure of larval trematodes in the pulmonate snail Helisoma anceps. Journal of Parasitology, 77: 540-550.

Geraerts, W., J. Joosse. 1984. Freshwater snails (Basommatophora). Pp. 141-207 in A Tompa, N Verdonk, J van den Biggelaar, eds. The Mollusca, Vol. 7, reproduction. London: Academic Press, Inc.

Herrmann, S., W. Harman. 1975. Population studies on Helisoma anceps (Menke) (Gastropoda: Planorbidae). Nautilus, 89: 5-11.

Jokinen, E. 1985. Comparative life history patterns within a littoral zone snail community. Verh. Internat. Verein, Limnol., 22: 3292-3399.

Laman, T., N. Boss, H. Blankespoor. 1984. Depth distribution of seven species of gastropods in Douglas Lake, Michigan. Nautilus, 98: 20-24.

Pip, E. 1987. Ecological differentiation within genus Helisoma (Gastropoda: Planorbidae) in central Canada. Nautilus, 101: 33-44.

Weber, L., D. Lodge. 1990. Periphytic food and predatory crayfish: Relative roles in determining snail distribution. Oecologia, 82: 33-39.

Zelmer, D., G. Esch. 1998. Bridging the GAP: The odonate naiad as a paratenic host for Halipegus occidualis (Trematoda: Hemiuridae). Journal of Parasitology, 84: 94-96.

Zimmerman, M., K. Luth, L. Camp, G. Esch. 2011. Population and infection dynamics of Daubaylia potomaca (Nematoda: Rhabditida) in Helisoma anceps. Journal of Parasitology, 97/3: 384-388.

University of Michigan Museum of ZoologyNational Science Foundation

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Mulcrone, R. 2014. "Helisoma anceps" (On-line), Animal Diversity Web. Accessed March 02, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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