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Montana Field Guide

Montana Field Guides

Northwest Striate - Striatura pugetensis
Other Names:  Patulastra pugetensis, Radiodiscus hubrichti


Global Rank: G5
State Rank: SNR

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General Description
A very small shell, to 1.8 mm diameter and 0.5 mm in height, flattened heliciform with a low spire, to about 3 whorls. Shell coloration is pale translucent yellowish-green, inner 1 1/2 whorls with fine spiral threads (requiring magnification to see) then abruptly switching to close and regular and oblique axial riblets, the last whorl gradually expanding. Aperture is large, oblique, and rounded, without denticles (teeth); umbilicus is wide, more than 1/3 the diameter of the shell. The animal is translucent white with gray head and tentacles and a black patch over the lung (Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry (1946).

Diagnostic Characteristics
Differs from all other small heliciform shells by a combination of very small size (< 2 mm diameter), to 3.5 whorls with the last greatly expanding, flattened spire, wide umbilicus, translucent yellow-green color, and very fine spiral threads on the embryonic whorls (requiring magnification to see).

Species Range
Montana Range

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Range Comments
Alaska to Mexico and east to Montana; also on Kauai, Hawaii. In Montana, five records west of the Continental Divide from Flathead County, all in Glacier National Park. Elevation range is 1021 to 1256 m (3350 to 4120 ft). First reported in Montana in 1916 but not seen again until 2008. Range and abundance in Montana poorly documented; current status needs investigation. Up to five animals have been found at a single site (Hendricks 2012).

Summary of Observations Submitted for Montana
Number of Observations: 9

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Habitat
Mixed mesic conifer forest in moist sites at lower elevations. Canopy species include western hemlock, grand fir, Engelmann spruce, black cottonwood and western larch; secondary canopy includes alder, dogwood, paper birch and mountain ash. Found under woody debris, mossy mats and ferns, in leaf litter or duff. Habitat in Montana poorly understood (Hendricks 2012).

References
  • 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. 1946. Land Mollusca of North America (north of Mexico), Volume II Part 1. Academy of Natural Sciences of Philadelphia Monograph Number 3 (2):1-520.
  • Additional ReferencesLegend:   View Online Publication
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    • Berry, S.S. 1919. Mollusca of Glacier National Park, Montana. Proceedings of the Academy of Natural Sciences of Philadelphia 71:195-205.
    • 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. 2001. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36(2):1-51.
    • Hendricks, P. 2009. Terrestrial mollusk surveys in Glacier National Park during 2008, including an illustrated key to all documented species. Helena, Mont: Montana Natural Heritage Program.
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Citation for data on this website:
Northwest Striate — Striatura pugetensis.  Montana Field Guide.  .  Retrieved on , from