SPECIES FACT SHEET
Scientific Name:
Common Name:
Pygulopsis robusta (Walker, 1908)
Pyrgulopsis hendersoni (P. robusta) (Pilsbry, 1933)
Jackson Lake springsnail
Harney Lake springsnail
(also Lake Abert/ XL Ranch springsnail)
Columbia springsnail
Idaho springsnail
Pyrgulopsis new species (P. robusta)
Pyrgulopsis idahoensis (P. robusta)
Phylum: Mollusca
Class: Gastropoda
Order: Neotaenioglossa
Family: Hydrobiidae
Pyrgulopsis is a genus of tiny aquatic snails in the order Neotaenioglossa, family Hydrobiidae.
This genus of snails is the second largest genus of freshwater mollusks in North America,
consisting of over 120 species (Lysne et al. 2007). The four taxa mentioned in this document
belong to the subgenus Natricola, which was erected in 1965. The taxonomic relationships
between taxa in this subgenus have been recently re-evaluated using molecular DNA information
and morphological characters (Hershler and Liu 2004). Prior to Hershler and Liu’s work, both
Pyrgulopsis hendersoni and Pyrgulopsis new species “Columbia springsnail” were considered to
be closely related to Federally Endangered Pyrgulopsis idahoensis, the Idaho springsnail, and
another species, Pyrgulopsis robusta, which was considered endemic to Wyoming. Two other
taxa, previously recorded in some documents as P. new species, the Lake Abert springsnail and
the XL Ranch springsnail, were also considered to represent populations of P. hendersoni, the
Harney Lake springsnail.
Distinctions between species within the genus Pyrgulopsis have typically been made based on
the arrangement and number of glands on the penes and other reproductive structures due to
morphological similarities. Upon review of morphology and mitochondrial and nuclear DNA
sequences, Hershler and Liu (2004) determined that these four Natricola snails do not merit
recognition as distinct species and should instead be treated as a single species- P. robusta.
Based upon this new classification, the US FWS made a final ruling that removes P. idahoensis
from the Threatened and Endangered list (Federal Register 2007).
The following report is a description of the biology of P. robusta, which is known to occur in
four western states in the U.S. including Idaho, Oregon, Washington and Wyoming (Lysne et al.
2007). Isolated populations of P. robusta, previously considered separate species, will herein be
referred to as: the “Oregon closed basin population,” (formerly considered P. hendersoni) the
“Columbia River population,” (formerly P. new species) the “northwestern Wyoming
population,” (formerly P. robusta) and the “Snake River population” (formerly considered P.
idahoensis).
Technical Description:
The shell is relatively large for this genus, being 1.98-3.38 mm wide and 4.6-7.5 mm tall and is
ovate to narrowly conic, with 4.5-6.25 whorls that are weakly to moderately convex (Hershler
and Liu 2004). Overall color of the shell is clear white with a tan periostracum. The protoconch
consists of 1.3-1.4 whorls that are completely smooth, or have a weakly wrinkled apical section.
Teleoconch whorls are often shouldered, sculptured with well-developed collabral growth lines.
Body whorl is often sculptured with myriad faint spiral threads. Shell is narrowly umbilicate.
Operculum is ovate, multispiral and nucleus is eccentric. Tentacles are pale with darker patch
distal to eyespots. Snout is light to dark gray-brown and the foot is pale-dark gray. Additional
details on the morphology of this species can be found in Hershler and Liu (2004) and Hershler
(1994).
Life History:
Pyrgulopsis robusta is dioecious (individuals possess either male or female reproductive organs)
and oviparous (lays eggs) (Hershler 1998; Lysne et al. 2007). This species most likely
reproduces once in its lifetime (semelparous), laying an unknown number of eggs on hard
substrates. Depending upon ambient temperatures, juvenile snails hatch and disperse several
weeks after being laid. In the Snake River in Idaho, the emergence of young snails was greatest
in the summer and fall although information for snail emergence in Oregon is not available.
Young are extremely small, less than 1 mm in length. On average, P. robusta survives 382 days,
approximately one year, with evidence suggesting that some individuals can reproduce multiple
times, thus exhibiting an iteroparous reproductive strategy (Lysne et al. 2007).
Range, Distribution, and Abundance:
The type locality for the originally described taxa, the northwestern Wyoming population, was
found on the eastern border of Jackson Lake, WY, Elk Island and vicinity (Frest and Johannes
1995). Most recognized sites are in the Grand Teton National Park. Some sites near Jackson
Lake have been extirpated due to rising and falling water levels. Currently extant sites occur in
Yellowstone National Park and John D. Rockefeller National Parkway (Hershler 1994; Frest and
Johannes 1995; Bowler 2004).
The Oregon closed basin population of P. robusta was originally found at a spring south of
Burns in Harney County, OR. However, this site is now dry due to groundwater mining. This
population was most likely widespread in the Harney Lake and Malheur Lake areas, and the
Oregon Interior Basin (Frest and Johannes 1995). Currently in Oregon, P. robusta occurs in
isolated populations in the Oregon Interior Basin and in the South Fork Malheur River, in
Harney and Lake Counties, as well as one or two spring sites in the Lake Abert area of Lake
County, OR (Frest and Johannes 1995; Hershler 1998; Bowler 2004; NatureServe Explorer
2010).
The Snake River population has been found in the Snake River at numerous locations along a
stretch of 214 river miles (U.S. Fish & Wildlife Service 2005).
The Columbia River population was once common in the lower Columbia River from the eastern
Columbia Gorge to Wallula Gap; Sherman, Umatilla and Wasco Counties in Oregon, and also in
Washington based on the snails’ habitat needs (NatureServe Explorer 2010). The Columbia
River population is currently known to occur at 17 sites in Oregon and Washington (Frest and
Johannes 1995; Bowler 2004; Hershler and Liu 2004) in isolated populations from river mile 20
upstream 400 miles to below Priest Rapids dam (NatureServe Explorer 2010). In Oregon this
group of snails has been reported from Wasco, Sherman and Umatilla Counties, and it has also
been reported in several counties in Washington.
Habitat Associations:
This species of snail typically occupies coldwater habitats, predominantly large springs, as well
as spring-influenced portions of streams, lakes, rivers (Frest and Johannes 1995) and reservoirs
(Stephenson et al. 2004). P. robusta has been found on a variety of substrates. In the Snake
River, Stephenson et al. (2004) found the species to prefer gravel to cobble-size substrates. Frest
and Johannes (1995) also found P. robusta to utilize similar habitat in the Columbia River. P.
robusta was found on cobbles embedded in sediments and on woody debris and macrophytes in
Polecat Creek and a single tributary (Riley 2003). In southeastern Oregon this species was found
on substrates ranging from coarse sand to cobble, but could also be associated with aquatic plants
Eleocharis, Rorippa, or Scirpus (Frest and Johannes 1995; Hershler 1998). Due to the variety of
conditions utilized by different populations of P. robusta, it is difficult to determine the variables
important for habitat selection. This species has been collected from water containing widely
varying dissolved oxygen concentrations, and field and laboratory studies indicate that P.
robusta can tolerate a wide temperature range (Lysne et al. 2007). Populations in the Snake
River have been found in water ranging in temperature from 4ºC to 26ºC (Stephenson et al.
2004). In southeastern Oregon, this species of snail has been found primarily in thermally stable,
cold springs and pools varying in size (Frest and Johannes 1995).
Threats:
If all individuals at an isolated site are killed in one incident, the entire population may be
extirpated since this species of snail is an annual species. Re-colonization of these isolated
wetlands is uncertain if a population is extirpated. Each documented site is considered
important in order to maintain the current distribution of this species.
Perennial water quality is a major determining factor for the persistence of this species of snail at
spring sites (Frest and Johannes 1995). Reducing groundwater discharge at springs or seeps may
result in adverse changes to water chemistry and habitat quality in downstream habitats. Entire
populations may die if sites become dewatered, due to diversion of spring outflow or lowering of
the water table. Capping of springs for irrigation, stock watering and human consumption is
becoming more common and other commercial uses of water such as groundwater pumping and
geothermal projects pose threats to the maintenance of a stable water table and natural
hydrologic function in these basins. Grazing cattle can degrade sites from trampling, fecal and
urine pollution, and the removal of vegetation. Humans have also caused habitat degradation
from trampling and pollution and have introduced exotic species of snails and fish to some sites.
Sites in rivers and on lake margins may be threatened by impoundments and siltation. Sites in
the Columbia River with populations of P. robusta have habitat characteristics approximating
pre-impoundment conditions. Some sites have been lost due to dredging and channel
improvements in the river. Agricultural runoff may affect the health of remaining populations.
Fluctuating water levels caused by drought or drawdowns for irrigation or power generation may
adversely affect lake and river site populations. An exotic species of gastropod, the New
Zealand mudsnail (Potamopyrgus antipodarum), has been documented in Crooked Creek,
Malheur County, and is abundant in the Snake River Basin (Frest and Johannes 2003; Lysne et
al. 2007). This species of gastropod exists in sympatry with the Jackson Lake springsnail (Riley
2003; Clark et al. 2006); however, P. antipodarum competes with the Wyoming population of P.
robusta and slows its growth.
Conservation Considerations:
Managing areas where this snail lives by restricting or prohibiting activities such as those
mentioned above will help protect this snail’s habitat. The development of streams is perhaps
the single most deleterious activity in arid and semi-arid ecosystems to terrestrial and freshwater
mollusks (Frest and Johannes 1995). However, any activity which affects the pristine aquatic
environment preferred by this species of snail will also adversely affect populations.
Conservation Status:
Pyrgulopsis robusta is globally ranked G4 (not rare) although at the state level in Oregon it is
ranked as S1 (critically imperiled due to extreme rarity) (Oregon Biodiversity Information Center
2010).
Overall, the trend of this species appears to be stable since multiple species of Pyrgulopsis have
been combined to form a single entity. However, certain populations, such as the Columbia
population in Oregon and Washington, and the northwestern Wyoming population are declining
(NatureServe Explorer 2010). The declining trend is due to habitat degradation and loss.
Prepared by: Heather Andrews
Date: April 2011
Final Edits: Rob Huff
FS/BLM Conservation Planning Coordinator
Date: June 2011
ATTACHMENTS:
(1)
(2)
(3)
Map of Range and Distribution
Shells of Natricola species
Information Sources
ATTACHMENT 1: Map of Range and Distribution
Figure 1. Known occurrences and distribution of Pyrgulopsis robusta in Washington, Oregon, Idaho, and
Wyoming. Image from U.S. Fish and Wildlife Service (2005).
ATTACHMENT 2: Shells of Natricola species
Figure 2. Shells of Natricola species. A, B. P. robusta, USNM 874185. C. P. hendersoni, USNM 874386. D, E.
P. hendersoni, USNM 892179. F, G. P. hendersoni, USNM 884547. H-J. P. idahoensis, ALBRCIDA 7568. K, L.
P. sp. A, USNM 883873. Scales = 1.0 mm. From Hershler and Liu (2004).
ATTACHMENT 3: Information Sources
Bowler, P.A. 2004. Petition to list the Jackson Lake springsnail (Pyrgulopsis robusta), Harney
Lake springsnail (Pyrgulopsis hendersoni), and Columbia springsnail (Pyrgulopsis new
species 6) as Threatened or Endangered. Report submitted to the United States Secretary
of the Interior, Washington, D.C., July 2004. 59 pp.
Clark ,W.H., M.A. Stephenson, B.M. Bean and A.J. Foster. 2006. Snake River aquatic
macroinvertebrate and ESA snail sampling. May 2005. Technical report submitted to:
U.S. Fish and Wildlife Service, Boise, Idaho in fulfillment of Section 10 permit
#7999558-5 requirements. 48 pages & 14 appendices. IN Lysne et al. 2007. The life
history, ecology, and distribution of the Jackson Lake springsnail (Pyrgulopsis robusta
Walker 1908). Journal of Freshwater Ecology 22: 647-653.
Federal Register. 2007. Final Rule to Remove the Idaho Springsnail (Pyrgulopsis idahoensis)
from the list of Endangered and Threatened Wildlife, August 6, 2007.
Frest, T.J. and E.J. Johannes. 1995. Interior Columbia Basin mollusk species of special
concern. Final report: Interior Columbia Basin Ecosystem Management Project. Contrac
#43-OEOO-4-9112, Walla Walla, WA.
Frest, T.J. and E.J. Johannes. 2003. Progress Report, Owyhee Mollusk Inventory. Vale
District BLM, Vale, OR.
Hershler, R. 1994. A review of the North American freshwater snail genus Pyrgulopsis
(Hydrobiidae). Smithsonian Contributions to Zoology 554: 1-115.
Hershler, R. 1998. A systematic review of the hydrobiid snails (Gastropoda : Rissooidea) of the
Great Basin, western United States. Part I. Genus Pyrgulopsis. Veliger 41: 1-132.
Hershler, R. and H.P. Liu. 2004. Taxonomic reappraisal of species assigned to the North
American freshwater gastropod subgenus Natricola (Rissooidea: Hydrobiidae). The
Veliger 47: 66-81.
Lysne, S.J., L.A. Riley, W.H. Clark and O.J. Smith. 2007. The life history, ecology, and
distribution of the Jackson Lake springsnail (Pyrgulopsis robusta Walker 1908). Journal
of Freshwater Ecology 22: 647-653.
NatureServe Explorer. 2010. Comprehensive Report for Pyrgulopsis robusta.
http://www.natureserve.org/
Oregon Biodiversity Information Center. 2010. Rare, Threatened and Endangered Species of
Oregon. http://orbic.pdx.edu/documents/2010-rte-book.pdf
Riley, L.A. 2003. Exotic species impact: eploitative competition between stream snails. M.S.
Thesis, Washington State University, Pullman, Washington, USA. 48 pages. IN Lysne et
al. 2007. The life history, ecology, and distribution of the Jackson Lake springsnail
(Pyrgulopsis robusta Walker 1908). Journal of Freshwater Ecology. 22: 647-653.
Stephenson, M.A., B.M. Bean, A.J. Foster and W.H. Clark. 2004. Snake River Aquatic
Macroinvertebrate and ESA Sanil Survey. Idaho Power Company Technical report
submitted to: U.S. Fish and Wildlife Service, Boise, Idaho in fulfillment of Section 10
permit #799558-4 requirements. 62 pages & appendices. IN Lysne et al. 2007. The life
history, ecology, and distribution of the Jackson Lake springsnail (Pyrgulopsis robusta
Walker 1908). Journal of Freshwater Ecology 22: 647-653.
U.S. Fish & Wildlife Service. 2005. Draft Best Available Biological Information for Four
Petitioned Springsnails in Idaho, Oregon, Washington, and Wyoming, pp. 82. Boise, ID.