Helisoma anceps

Geographic Range

The two-ridge rams-horn snail, Helisoma anceps, is found throughout North America. This species ranges from as far north 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)


Helisoma anceps inhabits permanent water bodies and is found among vegetation on various substrates. In Canada, H. anceps is more frequently found in lakes than in rivers or creeks, but in general has a broad distribution. This species is also found in highly organic substrates such as peat. In a Northern Michigan lake, H. anceps inhabited areas ranging from 0.5 to 9 m, but were mainly found at 6 m depths. As with other freshwater snails, H. anceps may migrate up and down in response to food and water temperatures. Substrates it seems to prefer include littoral silt and detritus. (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

Physical Description

Adult size of Helisoma anceps varies, from 8 mm to 16 mm in diameter. Color varies, but may be tannish to white. As with other planorbid snails, H. anceps is coiled to the left ("sinistral") in one plane. Helisoma anceps shells vary in shape throughout its range. The spire is an inverted cone, deep and narrow. The underside also is inverted and conical, but is more blunt or rounded at the end. There are ridges on both sides of the shell (the name "anceps" means "two sided" or "two heads"). The last whorl has a thickened and flared opening, or aperature. The foot is wide, rounded in front and back, and may have tiny white dots. This species has a single pair of tentacles with eye spots at the base. The tentacles are long and slender, extending beyond the foot. Since the respiratory pigment in the blood is hemoglobin, the soft parts of the snail appear reddish. (Burch and Jung, 1992; Burch, 1989)


In general, planorbid snails lay eggs in masses that protect them and help development. The time to development is likely temperature dependent. Mature specimens have a thickened lip on the shell. (Burch and Jung, 1992; Burch, 1989; Geraerts and Joosse, 1984)


Helisoma anceps is hermaphroditic. While the specific breeding season is unknown, it likely reproduces in the spring and summer. Although specific mating behavior for H. anceps is not known, encounters with other individuals or increased temperature induces mating in similar species. (Burch and Jung, 1992; Geraerts and Joosse, 1984)

After copulation, egg masses are attached to substrates, possibly rocks, stones, or macrophytes. About 20 to 30 eggs are in each mass. Egg mass production decreases when population densities increase in similar species. Female reproduction increases with food quantity and quality. (Geraerts and Joosse, 1984)

  • Breeding season
    Helisoma anceps breeds in the warmer months of the year.

Although the snails do not care for eggs after they are laid, the egg masses provide a protective environment to prevent predation, infections, and to support development. (Geraerts and Joosse, 1984)

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


Helisoma anceps likely lives two to three years. Aquatic pulmonates in general need stores of reserves to survive winter. (Burch and Jung, 1992; Zimmerman, et al., 2011)

  • Typical lifespan
    Status: wild
    2 to 3 years


While other pulmonate snails may move seasonally or daily, Helisoma anceps tends to stay in one place. In a northern Michigan study, released snails moved a distance of 1.6 m within 48 hours. Most movement was within the first 10 hours of release. Helisoma anceps may use chemosensory stimulation to move to areas with higher food sources such as periphyton. (Boss, et al., 1984)

Home Range

Helisoma anceps typically remains in the same general area, potentially moving a few meters at the most. (Boss, et al., 1984)

Communication and Perception

Planorbid snails in general have a more centralized nervous system. Helisoma anceps has eye spots at the base of its tentacles, which perceive light. Chemosenses are also used to find its food. (Burch and Jung, 1992; Burch, 1989)

Food Habits

Helisoma anceps grazes on bacteria, protists, and algae, using its radula (toothed ribbon structure). Chemoreception may be used to detect food. This species loosely prefers areas with higher periphyton sources. In general, nitrogenous food availability may limit populations. (Burch and Jung, 1992; Burch, 1989; Weber and Lodge, 1990)

  • Plant Foods
  • algae


Predators of H. anceps include the ribbon leech, Nephelopsis obscura, crayfish, fish and birds. Observations in a lake in Wisconsin showed snails were absent where crayfish were present. (Brown and Strouse, 1988; Dillon, et al., 2006; Weber and Lodge, 1990)

Ecosystem Roles

Freshwater snails in general graze on algae and H. anceps in particular tends to prefer substrates with algae. This species is also a known prey item for crayfish and other predators. Freshwater snails are often intermediate hosts for trematodes. Long term studies of H. anceps found prevalence of the trematode Halipegus occidualis was 60% in late June-early July in North Carolina, where it is an intermediate host. Helisoma anceps is a definitive host for nematode Daubaylia potomaca. (Esch, et al., 1997; Zimmerman, et al., 2011)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of Helisoma anceps on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Helisoma anceps on humans.

Conservation Status

Helisoma anceps has no known conservation status.


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



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.

World Map

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.


uses smells or other chemicals to communicate


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


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


union of egg and spermatozoan


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


having the capacity to move from one place to another.

native range

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


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season


remains in the same area


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


2003. "Helisoma anceps" (On-line). Encyclopedia of Life. Accessed July 02, 2013 at http://eol.org/pages/452823/overview.

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 http://www.fwgna.org/species/planorbidae/h_anceps.html.

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.