Carinate Mountainsnail - Oreohelix elrodi
The shell is large, to 28 mm diameter, height to 13 mm, but usually about 22 mm in diameter and 10 mm in height, heliciform with up to 5 to 5 1/2 whorls (new-born young about 3.5 mm in diameter, with 2 to 2 1/2 whorls), strongly depressed with a low spire, acutely carinate, with an open umbilicus to 6 mm diameter. Shell opaque and chalky, color is pale grayish to nearly white, sometimes with a very pale pinkish undertone; smaller shells may have a brownish cuticle that is lost in mature individuals. Inner (embryonic) whorls smooth then unevenly striate, later whorls lack spiral bands and are coarsely and irregularly ribbed on upper and lower surfaces, the last whorl descending somewhat to the aperture; the aperture is angular at the keeled periphery. Description for an alpine population on the Scapegoat Plateau is much as above except the shells are much smaller, to 15 mm diameter, 6.5 mm in height, and 4 1/2 whorls, but usually 10.5 mm diameter, 5 mm in height, and 4 whorls or less (Hendricks 1998, 2012; Hendricks et al. 2008; Burke 2013). Internal anatomy described by Pilsbry (1939) and Fairbanks (1984).
Active in wet and cool weather; otherwise not described.
A combination of shell shape (flattened heliciform or flattened conic), large size (except alpine form, which is medium size), opaque shell color (especially chalky white when dead) with a few bands, absence of reflected lip, and absence of teeth in the aperture distinguishes this from other Montana land snails (Hendricks 2003, 2012; Burke 2013). Oreohelix elrodi is very unique in appearance from other Montana Oreohelix. It is medium to large and stongly depressed (flattened), acutely carinate (keeled), and the later whorls are coarsely sculptured with a series of ribs especially evident on the underside.
Montana endemic: 29 records from five sites in two counties west of, or near, the Continental Divide: Lake (28), Lewis and Clark (1). Elevation range 1097 to 2438 m (3600 to 8000 ft). Original description based on specimens collected in 1899 from slopes above McDonald Lake in the Mission Mountains, Lake County. Animals from the Scapegoat Plateau, Lewis and Clark County may be an unsubscribed subspecies or entirely different species. Populations in the Mission Mountains are probably isolated from those in the Scapegoat Plateau and Swan Range. Sometimes locally abundant; as many as 100 live animals and 400 shells were seen at the Lewis and Clark County site in late July (Hendricks et al. 2008; Hendricks 2012; Burke 2013).
Observations in Montana Natural Heritage Program Database
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(Observations spanning multiple months or years are excluded from time charts)
Predicted Distribution in Montana
Predicted distribution model for Carinate Mountainsnail (Oreohelix elrodi)
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
Non-migratory. May may vertical movements through talus and boulder fields (Hendricks 1998).
Described originally as exposed limestone talus below tree line, but examination of the rock at four of five sites revealed they are predominantly argillite, sometimes with diorite or minor amounts of limestone. Occupied sub-alpine talus sites may lack forest canopy altogether or occur under an open mixed conifer canopy including Douglas-fir, western larch, ponderosa pine, western redcedar (near streams), with aspen, paper birch and mock orange scattered along the margins of talus slopes. The exception is an expanse of limestone well above tree line on the Scapegoat Plateau. Live animals present mostly within the talus under or on rocks, or in accumulations of duff within the talus (Hendricks 1998, 2012; Hendricks et al. 2008).
Not described. May feed on leaf detritis and duff (Hendricks 1998).
Hermaphroditic (Pilsbry 1939; Fairbanks 1984), otherwise not described.
Threats or Limiting Factors
Habitat occupied by Oreohelix elrodi (low-elevation slopes of mixed conifers, especially Douglas-fir, Ponderosa Pine and Western Larch) is threatened to some extent by logging, grazing, and fire, although occupied habitat is often in talus surrounded by mixed coniferous forest. Habitat requirements and food habits are poorly understood, however. Fire suppression efforts (especially use of fire retardants) and talus destabilization (trail maintenance, modification) could have negative impacts, as could chemical control of weeds (Frest and Johannes 1995; Hendricks 2003). The alpine site on the Scapegoat Plateau is most threatened by changes in climate.
- 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.
- Fairbanks, H.L. 1984. A new species of Oreohelix (Gastropoda: Pulmonata: Oreohelicidae) from the Seven Devils Mountains, Idaho. Proceedings of the Biological Society of Washington 97(1):179-185.
- 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.
- Hendricks, P. 1998. Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod 1901) in the Mission Mountains, Montana, with comments on Oreohelix elrodi (Pilsbry 1900). The Nautilus 112(2): 58-62.
- Hendricks, P. 2003. Status and conservation management of terrestrial mollusks of special concern in Montana. Unpublished report prepared for the U.S. Forest Service. Montana Natural Heritage Program, Helena, Montana. 67 pp. + appendices.
- 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.
- Hendricks, P., B.A. Maxell, S. Lenard, and C. Currier. 2008. Surveys and predicted distribution models for land mollusks on USFS Northern Region Lands: 2007. Report to the USDA Forest Service, Northern Region. Helena, MT: Montana Natural Heritage Program. 12 pp. + appendices.
- 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
Do you know of a citation we're missing?
- Elrod, M.J. 1902. A biological reconnoissance in the vicinity of Flathead Lake. Bulletin of the University of Montana Number, Biological Series 10(3):89-182.
- Elrod, M.J. 1901b. Montana shells. Rocky Mountain Magazine (May) 2(3):691-697.
- Elrod, M.J. 1903a. Notes on Pyramidula elrodi [Oreohelix elrodi] Pils. The Nautilus, 16:109-112.
- Pilsbry, H.A. 1900. Notices of new American land snails. The Nautilus 14:40-41.
- Stabins, H. 2004. Forest owl and invertebrate monitoring report for northwestern Montana Plum Creek managed landscapes for 2003 and 2004. Plum Creek.
- Additional Sources of Information Related to "Snails / Slugs"