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 bedfordensis: shell ovate-conic, protoconch about 1.25 whorls, empty shell clear white, periostracum brown or tan, aperture ovate to pyriform, inner lip slightly thickened, columellar lip strongly reflected, outer lip thin, umbilicus narrowly perforate and often obscured by columellar lip; operculum medium thickness, light amber with darker red hue in nuclear region, ovate; cephalic tentacles gray to black, head and foot brown to dark brown. Shell height 2.94-3.69 mm, shell width 1.99-2.30 mm, aperture (height x width) 1.31-1.59 x 1.27-1.47 mm, total shell whorls >4.0-5.0, width of body whorl 1.71-2.10 mm, shell width/shell height 0.58-0.70 (Hershler and Gustafson 2001); Shell height 2.29-3.30 mm, shell width 1.53-2.06 mm, aperture (height x width) 1.12-1.54 x 0.95-1.23 mm, total shell whorls 4.25-5.0, width of body whorl 1.29-1.81 mm, shell width/shell height 0.62-0.73 Hershler et al. 2008).

Adults presumably active throughout the year.

Small and globose with an operculum; compared to P. blainica (the only other member of the genus in Montana, and restricted to a single Madison County spring), P. bedfordensis typically smaller in all shell dimensions, teleoconch whorls less convex, aperture more angular at adapical end, columellar shelf wider, also with differences in genitalia (larger penial lobe, smaller penial filament, absence of a ventral penial gland), narrower central cusps on central radular teeth, and mtDNA sequences; shell ratios of P. bedfordensis larger than P. blainica, with shell width 58-73% of shell height (vs 51-69%) and aperture height 45-54% of shell height (vs 32-47%) (Hershler and Gustafson 2001; Hershler et al. 2008).

Sedentary.

Found on the substrate (sand, gravel and cobbles) and aquatic plants in the discharge of a single warm spring (21.0-23.6 C) on the west side of Canyon Ferry Reservoir. Very dense population sampled in 2015, average densities of the springsnail were 30,540 live individuals per meter squared (SE = ±2,625) and 17,353 dead individuals per meter squared (SE = ± 1,389). Snail shells literally carpeted the bottom substrate of the spring channel (Hershler and Gustafson 2001; Stagliano 2016).

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 and Gustafson 2001), reproductive characteristis not described.

The riparian habitat and water recharge to the spring where it is found should be protected.

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.