Montana Field Guide

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.

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).

Sedentary.

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.

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

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.

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.