SPECIES FACT SHEET
Species Common Name: Nerite Rams-horn
Species Scientific Name: Vorticifex neritoides, Baker 1945
Phylum: Mollusca
Class: Gastropoda
Order Basommatophora
Family: Planorbidae
Type Locality: “Lower Columbia River” probably at the Dalles, Wasco
Co., OR (Frest and Johannes 1995). Type locality considered extirpated.
OR/WA BLM and FS Region 6 Units where Suspected or
Documented:
Columbia River Gorge National Scenic Area (suspected).
Technical Description:
Shell similar to that of V. effusa, but smaller, with a lower spire, few
whorls and comparatively thicker shell.
Life History:
Semelparous – lives 1-2 years, breeds and dies. Population turn over is
probably greater than 90%.
Freshwater pulmontates generally reproduce by copulation and crossfertilization. Eggs are laid from spring to autumn in gelatinous capsules
attached to plants, stones, or other objects. They lack a free-swimming
larval stage, and hatch as young snails, anatomically complete except for
the reproductive system (Hyman 1967).
Feed by scraping algae and diatoms from rock surfaces in stream. May
occasionally feed on other plant surfaces. Present all year, but not active
in winter. Individuals have no lungs or gills with respiration through the
mantle cavity.
Range, Distribution (Current and Historic), and Abundance:
Formerly occurred from the Dalles to the mouth of the Columbia River
(Frest and Johannes 1995). Frest and Johannes (1995) also report that
this species could not be relocated at the “type locality” at the Dalles in
1988, and only one new location on the north side of the Columbia was
found during surveys at this time. The lower Columbia River
populations, including the type location, are largely extirpated due to
habitat modification caused by BPA dams and impoundments although
1
one occurrence is known from the north side of the river. No specific
information on abundance found.
Habitat Associations:
Since this species is so rarely found, habitat associations given here are
general. Generally found in relatively deep rivers, in unpolluted, swiftflowing, highly oxygenated water on stable (boulder-gravel) substrate,
such as in the vicinity of rapids or other unimpounded stretches.
Threats:
Hydropower development on the Columbia River has destroyed much of
this species former habitat. Also, irrigation diversions, siltation and
fluctuations in dissolved oxygen caused by pollution have also
contributed.
Frest and Johannes (1995) report the following threats: impoundment
and damming of much of the original habitat; sedimentation; orchard
runoff; nutrient enrichment due to agricultural practices, pulp mill
effluents; metal smelting residues and discharges.
Conservation Considerations:
(1) Control siltation and pollution, (2) prevent fluctuations in dissolved
oxygen.
Prepared by: Nancy Duncan, April 2008
Edited by Rob Huff, April 2009
References
Baker, F. C. 1945. The Molluscan Family Planorbidae. University of
Illinois Press, Urbana, Illinois, 530 pp.
Burch, J. B. 1982. Freshwater snails (mollusca: gastropoda) of North
America. Environmental Monitoring and Support Laboratory. U.S.
Environmental Protection Agency. Contract No. 68-03-1280. Cincinnati,
Ohio.
Frest, T. J., and E. J. Johannes. 1995. Interior Columbia Basin mollusk
species of special concern. Final report: Interior Columbia Basin
Ecosystem Management Project, Walla Walla, WA. Contract #43-0E00-49112. 274 pp. plus appendices.
Hyman, L. L. 1967. The invertebrates. Vol VI. Mollusca I. McGrawHill, New York. 792 pp.
2
USDA/USDI. 1994. Final supplemental environmental impact
statement on management of habitat for old-growth forest related species
within the range of the Northern Spotted Owl: Appendix J2 results of
additional species analysis. Portland, Oregon
3