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Montana Field Guide

Montana Field Guides

Blaine Pyrg - Pyrgulopsis blainica

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Species of Concern
Native Species

Global Rank: G1
State Rank: S1
(see State Rank Reason below)

Agency Status

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State Rank Reason (see State Rank above)
Due to this restricted distribution and only known occurrence, this species was given a conservation status rank, G1 (Globally Rare) and placed on the MT Species of Concern list as S1, critically imperiled
General Description
Tiny, operculate snails (2-5 mm in height) usually endemic to thermally-warmed springs in the western U.S. Pyrgulopsis is the largest genus of freshwater gastropods in North America.

Pygurlopsis blainica: shell ovate-conic, protoconch about 1.4 whorls, periostracum dark brown, aperture ovate to weakly angled adapically, inner lip usually thickened, columellar shelf narrow or absent, outer lip thin to slightly thickened, umbilicus absent (rarely perforate); operculum fairly thick, reddish, ovate; cephalic tentacles dark brown dorsally, head and foot dark brown. Shell height 3.54-4.62 mm, shell width 2.19-2.93 mm, aperture (height x width) 1.31-1.94 x 1.21-1.61 mm, total shell whorls 4.50-5.50, width of body whorl 1.93-2.43 mm, shell width/shell height 0.52-0.69, aperture height/shell height 0.32-0.47 (Hershler et al. 2008).

Adults presumably active throughout the year.

Diagnostic Characteristics
Small and globose with an operculum; compared to P. bedfordensis (the only other member of the genus in Montana, and restricted to a single Broadwater County spring), P. blainica typically larger in all shell dimensions, with a relatively narrower shell and relatively smaller aperture, teleoconch whorls more convex, aperture less angular at adapical end, columellar shelf narrow or absent, also with differences in genitalia (smaller penial lobe, larger penial filament, presence of a ventral penial gland), broader central cusps on central radular teeth, and mtDNA sequences; shell ratios of P. blainica smaller than P. bedfordensis, with shell width 51-69% of shell height (vs 58-73%) and aperture height 32-47% of shell height (vs 45-54%) (Hershler et al. 2008).

Species Range
Montana Range


Range Comments
Montana endemic: restricted to the discharge of two cold water springs, in a bypass channel above and outflow below the Ennis National Fish Hatchery, Madison County, at about 1700 m elevation (Hershler et al. 2008). This is the second species of the genus found on the east side of the Continental Divide, Pygurlopsis bedfordensis in Broadwater County being the first (Hershler and Gustafson 2001; Stagliano 2016).

Observations in Montana Natural Heritage Program Database
Number of Observations: 3

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


Cold water spring discharge (about 945 l/s at 12.0 C) over a distance of several hundred meters, in seemingly natural bypass channel, where snails extremely abundant, and hatchery outflow (Hershler et al. 2008); other details not provided.

Food Habits
Not described. Freshwater aquatic snails are mostly scrapers of algae and other photosynthetic biofilms on underwater surfaces (rocks, aquatic plants).

Reproductive Characteristics
Sexes separate, not hermaphroditic. Other than anatomy of male and female reproductive systems (Hershler et al. 2008), reproductive characteristis not described.

The riparian habitat and water recharge to the spring where it is found should be protected. The springs have been highly modified for use by the fish hatchery (constructed in 1931) and are now enclosed in buildings, with most discharge piped underground to the hatchery. A small fraction of the discharge runs for a few hundred meters in a bypass channel before entering a pipe.

Threats or Limiting Factors
Damage to the riparian habitat or any harmful discharges (chemicals, pollutants, etc.) into the water recharge area of the spring where this species is found could have detrimental effects on the one population in the state.

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Citation for data on this website:
Blaine Pyrg — Pyrgulopsis blainica.  Montana Field Guide.  .  Retrieved on , from