Rocky Mountainsnail - Oreohelix strigosa
Helix strigosa, Patula strigosa
Highly variable in form. Medium-sized to large, the shell diameter ranges from 9 to 28 mm, depending on subspecies, but usually more than 15 mm (new-born young about 3 mm diameter), and from 6 to 18 mm in height but usually less than 14 mm. Typically flattened heliciform, with 4 1/3 to 5 3/4 whorls, but varies from elevated to depressed in profile; the periphery is weakly to sharply angular. Umbilicus is relatively broad and deep, the aperture ovate to rounded, lip barely thickened inside. Shell opaque and chalky, color is grayish (dead shells to pearly white), with a series of reddish-brown spiral bands, typically one on the upper surface and another just below the periphery, sometimes with one or more fainter bands below that; bands may be evident on penultimate whorl, or may be very pale or absent entirely, probably from abrasion and exposure to sunlight. Shell surface with coarse, irregular axial riblets and striae, sometimes with faint spiral sculpting as well (Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry (1934) and (1939).
Possible subspecies: O. s. capex, O. s. fragilis and O. s. goniogyra in Idaho only; O. s. berryi and O. s. cooperi in Montana only; O. s. strigosa and O. s. depressa in both states.
Validity, status and distribution of the various subspecies need additional study. Oreohelix strigosa probably includes a multitude of full species lumped under one name; O. s. cooperi already is treated as a full species by some authors. Oreohelix strigosa berryi described originally in 1915 from specimens collected in Swimming Woman Creek Canyon of the Big Snowy Mountains in Golden Valley County.
Medium to large size, calcareous whitish to gray, somewhat flattened to moderately elevated spire, variable banding, relativley broad umbilicus, absence of refelcted lip, and surface sculpture help distinguish this from most other larger shells. Typical O. subrudis has a higher spire and smaller umbilicus, O. yavapai has a much flatter profile, broader umbilicus, and oblique and oval aperture.
Western North America, from British Columbia and Alberta south to Nevada, Arizona and New Mexico. In Montana, reported on both sides of the Continental Divide from 22 counties. Elevation range is 661 to 2623 m (2170 to 8605 ft). May be abundant at some locations; more than 100 shells were reported at single sites in Broadwater and Fergus counties and 30 live individuals at one Carbon County site (Hendricks 2012).
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(Observations spanning multiple months or years are excluded from time charts)
Predicted Distribution in Montana
Predicted distribution model for Rocky Mountainsnail (Oreohelix strigosa)
Records were spatially unique and had a locational uncertainty of ≤ 400 meters.
Hotter colors indicate areas that are predicted to have more suitable habitat for the species.
Black dots are positive data used to build the model.
Gray dots are locations where a survey capable of detecting the species has been performed.
Landownership, a shaded relief map, and county lines are included for reference.
Details of the modeling effort, a description of the environmental layers used, and a more thorough interpretation
of model outputs can be found in the report Land Mollusk Surveys and Predicted Distribution Models on USFS Northern Region Lands: 2007
More model output for this species
Near streams, moister forested locations, and in drier sites including talus slopes and vegetated rockslides or stony ground; O. s. berryi associated with limestone. Canopy species include Douglas-fir, lodgepole pine, ponderosa pine, western redcedar, western hemlock, western larch, Engelmann spruce, rocky mountain juniper, aspen, black cottonwood, mountain maple, alder, and willow. Live animals present mostly under rocks or wood and in duff or soil accumulations; sun-bleached shells may be found on the surface (Hendricks 2012).
- Literature Cited AboveLegend: View Online Publication
- Burke, T. E. 2013. Land snails and slugs of the Pacific Northwest. Corvallis, OR: Oregon State University Press. 344 p.
- Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.
- Pilsbry, H.A. 1934. Notes on the anatomy of Oreohelix, III with descriptions of new species and subspecies. Proceedings of the Academy of Natural Sciences of Philadelphia 85:383-410
- Pilsbry, H.A. 1939. Land Mollusca of North America (North of Mexico), Volume 1, Part 1. Monograph of the Academy of Natural Sciences of Philadelphia Monograph Number 3 (1): 1-573.
- Additional ReferencesLegend: View Online Publication
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- Berry, S.S. 1916. Notes of Mollusca of central Montana. Nautilus 29:124-128.
- Elrod, M.J. 1903b. Montana shells - Pyramidula strigosa [Oreohelix alpina]. The Nautilus 17:1-6.
- Forsyth, R.G. 2004. Land snails of British Columbia. Royal British Columbia Museum: Victoria, British Columbia, Canada. 188 pp.
- Frest, T.J. and E.J. Johannes. 1995. Interior Columbia Basin mollusk species of special concern. Final report to the Interior Columbia Basin Ecosystem Management Project, Walla Walla, WA. Contract #43-0E00-4-9112. 274 pp. plus appendices.
- Frest, T.J. and E.J. Johannes. 2001. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36(2):1-51.
- Henderson, J. 1924. Mollusca of Colorado, Utah, Montana, Idaho, and Wyoming. University of Colorado Studies 13(2):65-223.
- Henderson, J. 1936. Mollusca of Colorado, Utah, Montana, Idaho, and Wyoming, supplement. University of Colorado Studies 23(2): 81-145.
- Russell, L.S. 1951. Land snails of the Cypress Hills and their significance. The Canadian-Field Naturalist 65:174-175.
- Smith, A.G. 1943. Mollusks of the Clearwater Mountains, Idaho. Proceedings of the California Academy of Sciences, fourth series, 23:537-554.
- Stabins, H. 2004. Forest owl and invertebrate monitoring report for northwestern Montana Plum Creek managed landscapes for 2003 and 2004. Plum Creek.
- Weaver, K.F., T. Anderson, and R. Guralnick. 2006. Combining phylogenetic and ecological niche modeling approaches to determine distribution and historical biogeography of Black Hills mountain snails (Oreohelicidae). Diversity and Distributions 12:756-766.
- Additional Sources of Information Related to "Snails / Slugs"