Physa natricina Taylor 1988, junior synonym of Physa acuta Draparnaud,
1805 (Pulmonata: Physidae)
D. CHRISTOPHER ROGERS 1,3 and AMY R. WETHINGTON 2
EcoAnalysts, Inc., 166 Buckeye Street, Woodland, California 95695, USA. Email:
Department of Biology, Chowan University, Murfreesboro, North Carolina 27855, USA. Email:
3 Corresponding author.
Running Head: Physa synonymy
Physa natricina Taylor, 1988 is reported as a narrow range endemic species from the Snake River in
Idaho, USA and is currently protected under the federal Endangered Species Act. We examined all
available type material as well as more than 1,500 specimens of Physa collected from the Snake River and
adjacent areas over the past twelve years and compared them to the original descriptions and the type
material. No material collected from the Snake River, nor from the paratype series, could be confidently
ascribed to P. natricina using both the internal and external morphological characters defined in the
original description, nor by direct comparison to the holotype. Furthermore, the holotype and paratypes all
have internal and external morphology that is accommodated within the natural range of variation of the
polymorphic Physa acuta Draparnaud, 1805. Therefore P. natricina is conspecific with P. acuta, a
common, widespread species.
Key words: Morphological species concept, Snake River, Idaho, endangered species, conservation,
mollusks, Gastropoda, freshwater snails.
Physidae is one of the most common and widely distributed families of pulmonate gastropods in the world
(Burch 1989; Dillon 2000; Dillon et al. 2002; Taylor 2003). Recent studies involving sequence data,
isozyme data, behavior and no choice breeding experiments (Dillon et al. 2002; Wethington & Guralnick
2004; Wethington 2004; Dillon & Wethington 2004; Dillon et al. 2005; Wethington & Lydeard 2007)
have revealed that the family is not as species rich as previously reported (Te 1975; Te 1978; Te 1980;
Burch 1982; Burch & Tottenham 1980; Turgeon et al. 1998; Taylor 2003), but is in reality composed of a
few, phenotypically plastic species (Crowl & Covich 1990; Covich et al. 1994; DeWitt 1998; DeWitt et
al. 1999; DeWitt et al. 2000; Burnside 1998; Britton & McMahon 2004).
Recently it has been demonstrated that two physid species believed to be rare, threatened or endangered
are not genetically or morphologically separable from P. gyrina Say, 1821 (Taylor 2003; Wethington &
Guralnick 2004). However, other narrow range endemics such as P. zionis Pilsbry, 1926, long been
ecognized as morphologically distinct (Chamberlain & Jones 1929; Te 1975; Te 1978; Te 1980; Burch
1982; Burch & Tottenham 1980; Taylor 2003), have been shown to be genetically unique (Wethington &
Guralnick 2004; Wethington 2004; Wethington & Lydeard 2007). Here, we examine the validity of Physa
natricina Taylor, 1988 using morphological methods.
Physa natricina was described as a narrow range, endemic species from recent material collected from
Idaho and from fossil material collected from Idaho, Utah and Nevada (Taylor 1988). Recent material
came from the Snake River in Gooding, Elmore and Owyhee counties, Idaho (Taylor 1988). Taylor (1988)
reported P. natricina as fossils in Pleistocene/Holocene deposits from Bear Lake (Idaho/Utah) and Lake
Bonneville (Nevada/Utah), from Box Elder County and Salt Lake County in Utah and from Caribou
County (Lake Thatcher) and the Snake River in Idaho. The United States Fish and Wildlife Service listed
the Snake River P. natricina (among other gastropod species) as an endangered species due to a decline in
the species’ range, which was attributed to manipulation of water by hydroelectric development and
project operations, water withdrawal and diversions, water quality degradation and inadequate regulatory
environmental protection mechanisms (USFWS 1992). The Snake River is part of the Columbia River
watershed. The Snake River starts in western Wyoming, heading south along the Idaho border, before
turning west, crossing Idaho and then turning north and crossing into Washington, where it joins the
Taylor (1988) reported that he placed the holotype specimen at the Los Angeles County Museum (under
the accession number LACM 2256) and paratype material at the University of Michigan Museum of
Zoology, Ann Arbor (UMMZ 230241, 230262, 229272, 229273, 229301 and 229388) and the US
Geological Survey (USGS 22427, 22448, and 23193). Additional material is referenced under the
accession numbers W2512 and W2514 and without accession numbers; however no indication is given
as to where these specimens were deposited. Taylor (2003) included P. natricina with the polymorphic,
nearly cosmopolitan Physa acuta Draparnaud, 1805 in his new tribe Haitiini and genus Hatia. It should be
noted that on the whole, Taylor’s (2003) higherlevel taxonomic revision of the Physidae has not been
supported by other analyses (Dillon et al. 2002; Wethington & Guralnick 2004; Wethington 2004; Dillon
& Wethington 2004; Dillon et al. 2005; Wethington & Lydeard 2007).
Materials and methods
We compared holotype and paratype material of P. natricina as deposited by Taylor (1988) with more
recently collected physids from the type locality (Snake River, Idaho), as well as with other species from
western North America.
Status of the type specimens
We contacted each museum mentioned by Taylor (1988) in order to view and examine both holotype and
paratype material deposited by him as Physa natricina. Taylor (1988) stated that the holotype (dry shell
and soft body preserved in ethyl alcohol) was deposited in the Los Angeles County Museum (LACM).
However, no such material was present. Eventually the holotype was found and examined, having been
deposited by Taylor in the California Academy of Sciences in San Francisco (CAS) in 1999 (accession
number 114795) (It should be noted that to prevent confusion, CAS has sent the holotype and paratype to
Taylor (1988) claimed that he deposited paratypes at the US Geological Survey (USGS) Western
Ecological Resource Center. However, the USGS claimed not to have any collections of mollusks and no
collections that used the numbering system reported in the original description. We were able to examine
the paratype material deposited in University of Michigan Museum of Zoology (UMMZ).
Additional Material Examined
The holotype and paratype specimens were directly compared with more than 1,500 Physa specimens,
preserved in ethyl alcohol collected between 1995 and 2007 (from approximately 7,000 samples) from
along a 233 mile stretch of the Snake River in Idaho [ranging between Lower Salmon Falls Dam (RM
573) and Cobb Rapids (RM 340)] by Idaho Power Company (IPC) and identified and analyzed by
EcoAnalysts, Inc. (Cazier & Myers 1996; Cazier 1997; Cazier 1999a; Cazier 1999b; Cazier 1999c; Cazier
Shinn 2001a; Cazier Shinn 2001b; Cazier Shinn 2001c; Cazier Shinn 2001d; Cazier Shinn 2001e; Cazier
Shinn 2002; Cazier Shinn et al. 2001), all deposited in the Orma J. Smith Museum of Natural History
(ALBRCIDA) in Caldwell, Idaho. This 233mile river reach includes the entire reported recent range of P.
natricina as well as 100 miles up and down stream of that range. Samples were collected within each river
mile throughout this area and included both shallow water (shoreline) and deepwater habitats. Samples
were excavated using a venturi loop dredging apparatus. Deepwater samples were obtained by utilizing
SCUBA equipment. EcoAnalysts, Inc. only identified these Physa specimens collected by IPC to genus.
An additional 137 Physa were collected and preserved in ethyl alcohol from lateral tributaries along this
233 mile reach of the Snake River, including Middle Line Canal, the C. J. Strike Reservoir, Brown’s
Creek, Bennet Creek, King Hill Creek, Billingsley Creek, Cedar Draw, Rock Creek, Southside Canal and
Attention was focused on Taylor’s (1988) description of both shell and anatomical characters of Physa
natricina in our examination of the holotype, paratypes, and topotypes. The defining external characters
for P. natricina are: 1) shell with inflated body whorl (length x width measured using a stage micrometer);
2) planes of aperture and growth lines conspicuously oblique to axis of coil; 3) axial sculpture of crowded
raised threads (dense growth lines); 4) tentacle with a dense black core of melanin in distal half only; 5)
body otherwise nearly colorless (Taylor 1988, p.67). Additional characters given include: 6) in dorsal
view the animal is amber, as seen through the shell; 7) mantle digitations are three at the posterior angle of
the aperture and three or four at the parietal surface; 8) mantle collar, mantle and mantle skirt are pale
amber gray (Taylor 1988, pp.71, 72). Furthermore, Taylor (1988) described the penial complex as:
preputium having a preputial gland onethird the length of the preputium, with two pilasters internally;
penial sac proximally expanded and slightly longer than the preputium; extremely large pyriform
sarcobellum which is distally papillate.
All material collected from the lateral tributaries and one to three specimens of the material deposited in
ALBRCIDA were chosen from each population for dissection and examination of the penial morphology.
Care was made to use Physa from the ALBRCIDA collections that most closely matched the Physa
natricina description and holotype. Using Te (1978) as an initial phylogenetic framework, the material
was partitioned into taxonomic groups.
Taylor (1988; 2003) stated that the diagnostic characters he used for P. natricina came from the holotype,
numerous paratype shells (the majority being fossil) and apparently only three living animals, one of
which Taylor dissected. However, Taylor’s diagnostic characters for the species P. natricina are not all
present in the paratype series:
1. “Shell with inflated body whorl”
The additional specimens from the Snake River vary in the form of the body whorl, from a broadly
inflated body whorl (length x width = 1:1) to a narrow body whorl (1.7:1). Photographs of the paratype
material provided by Taylor (1988, p. 68, Figure 6) reflect this same range of variation (compare 6d with
a, e, g, h and j).
2. “Planes of aperture and growth lines conspicuously oblique to axis of coil”
This was difficult to gauge in the recent material (both the holotype and our specimens), as the growth
lines sometimes varied from oblique to subparallel along the axis of growth or where animals had been
damaged. Furthermore, the vast majority of the fossil paratype specimens had all growth lines either
eroded nearly to obliteration or nonexistent. The growth lines were never consistently conspicuously
oblique in any of the material, including the types.
3. “Axial sculpture of crowded raised threads”
This character varied extensively between animals and even on individuals. The paratype specimens
UMMZ229301 are nearly smooth. Our material from the Snake River bore shells that are smooth, with
faint growth lines, with obvious raised threads or with two or all three character states on individual
specimens. One specimen (ALBRCIDA14940) has dense, raised growth lines on the body whorl up to a
healed break. After the break, the growth lines are fine and more regularly spaced. A second specimen
from the same lot had the opposite arrangement.
4. “Tentacle with a dense black core of melanin in distal half only”
Since the paratype material consists of empty shells or dried carcasses and the holotype is shriveled in
preservation, this character could not be adequately evaluated in the types. Our Snake River material
contains specimens without pigment in the tentacles, with entirely pigmented tentacles, pigment in the
basal half, pigment in the distal half and one specimen (ALBRCIDA26197) has one tentacle with
pigment in the basal half and one with pigment in the distal half.
5. “Body otherwise nearly colorless”
The dried corpses in paratype collection UMMZ229273 are entirely black in color. This is probably an
artifact of drying. Our Snake River material ranged from entirely black, to lightly pigmented to entirely
colorless in and between individual collections.
6. “In dorsal view the animal is amber, as seen through the shell”
The paratype series includes combinations of thick shells as well as translucent shells. It is impossible to
see the animal through the thick shells. The animals appear grey, amber or black through the thin,
translucent shells. Both thick and thinshelled specimens are present in all the recent samples.
7. “Mantle digitations are three at the posterior angle of the aperture, and three or four at the parietal
This character is nearly impossible to verify in the available material. Many of the mantle digitations are
so distorted by preservation that accurate assessment was not possible. However, the holotype appears to
have only two mantle digitations at the posterior angle of the aperture, contrary to the description.
8. “Mantle collar, mantle and mantle skirt are pale amber gray”
These structures varied from faintly to darkly mottled, pale gray to dark gray or black, or gray brown to
brown or amber in all Snake River material. The pattern varied extensively in and between individual
collections. In different individuals, mottling was reduced, limited to one area, or darker or lighter in
various areas. There was no consistency in this character.
Penial morphology was examined in 211 Physa specimens from the Snake River and tributaries. All
dissections revealed a Physa type b or type c penial morphology (following Te, 1978). Thirteen specimens
were of the Physa gyrina Say, 1921 group and 198 specimens were of the Physa acuta group.
Only the holotype of P. natricina was found to match the description found in Taylor (1988), although it
did not match in the number of mantle digitations. None of the more than 1,500 specimens examined
during this study conformed entirely to the diagnostic characteristics given in Taylor’s (1988) description
of P. natricina. The shell and penial characters as described by Taylor (1988; 2003) for P. natricina are
not appreciably different from the original description reported by Draparnaud (1805) for P. acuta. The
shell characters of Physa acuta have been shown to exhibit substantial phenotypic plasticity with regards
to biotic (Crowl & Covich 1990; Covich et al. 1994; DeWitt 1998; DeWitt et al. 1999; DeWitt et al. 2000)
and abiotic (Burnside 1998; Britton & McMahon 2004) factors. As such, shell characters in this group are
not entirely reliable.
All live Physa reported as P. natricina are less than 5 mm (Taylor 1988; 2003) and therefore are probably
juveniles. Frest (1991; personal comment) believes that P. natricina is P. integra, a junior synonym of P.
acuta (Dillon et al. 2002; Wethington 2004; Wethington & Lydeard 2007).
The difference between the penial morphology for P. natricina and that of P. acuta is described by Taylor
(1988; 2003) but not in any quantitative or definitive way. Both species have penial morphology c as
defined by Te (1975; 1978; 1980). Taylor (2003) reported that the penial complex of P. natricina differs
from P. acuta with regards to preputium to penial sheath length, with P. natricina having nearly equal
ratios of the two structures and P. acuta having a muscular sheath only about 0.75 as long as its
preputium. Taylor’s comparison of the sarcobellum differs between P. natricina and P. acuta with P.
natricina having a very large pyriform shaped sarcobellum bearing a single terminal papilla and P. acuta
having a minute paplilla at the top of an elongate sarcobellum. The size of the preputial gland was also
different between the two species as described in Taylor (2003) with P. acuta having a relatively small
preputial gland near the proximal end of the preputium while P. natricina’s preputial gland covers nearly
half of the proximal end of the preputium. However, based on many dissections of P. acuta across its
geographical distribution, the penial morphology characters are variable with regards to preputial gland
size, preputium to musculature penial sheath ratio or the shape and size of the sarcobellum. All these
character states were present individually or together in different combinations (Te 1975; Te 1978; Te
1980; Wethington & Lydeard 2007; Wethington in prep.). Therefore, the morphological differences in
penial morphology reported in Taylor (1988; 2003) are not valid distinguishing features for P. natricina.
The results of this study demonstrate that the diagnostic morphological characters of the P. natricina
holotype are not unique to any Physa taxon and cannot be used to define the species. Penial morphology,
as defined by Te (1975; 1978; 1980) has been shown as a perfect predictor of phylogenetic structure,
fitting perfectly with molecular analyses (Wethington 2004; Wethington & Guralnick 2004; Wethington
& Lydeard 2007). The penial characters of the holotype and by Taylor’s diagnoses are identical with the
widespread species Physa acuta. This character was consistent between the P. natricina holotype and all
P. acuta examined in this study. All the specimens collected from the Snake River system where the
penial morphology was examined were either P. acuta or P. gyrina. Therefore, we conclude that P.
natricina is a junior synonym of P. acuta.
While it could be argued that P. natricina did exist as a real species, but has since gone extinct due to the
habitat being invaded by P. acuta, we feel that this is extremely unlikely. First, fossil P. acuta are known
from all the same localities and more where fossil P. natricina was reported (Taylor 1988). Secondly and
more importantly, as shown above the characters of the type series, including the holotype are not unique,
do not conform to the original description and can be found in any of a myriad combinations across the
range of P. acuta, not just regionally, but globally. Because the definition for P. natricina is not specific
(i.e.: exclusive) it cannot be a species.
We thank the Orma J. Smith Museum of Natural History, Idaho Power Company, Los Angeles County
Museum, California Academy of Sciences for providing material. We acknowledge the following funding
sources: NSF (awarded to Lydeard, Dillon and Strong); Conchologists of America and Western Society of
Malacologists (awarded to Wethington); the University of Alabama Graduate Association and Biology
Department and the MultiUser Equipment Grant from NSF (awarded to Lydeard, Mayden, Powell and
Harris (DBI007351). R. Dillon and W. Clark provided valuable comments to earlier drafts. We are very
grateful to the following individuals who provided additional material: C. Albrecht, R. Anderson, C.
Appelton, P. Bouchet, L. Bousset, D. Britton, R. Bromley, P.A. Crochet, R. Dillon, A. Estoup, B. Facon,
G. Feulner, R. Rojas Garcia, R. Guralnik, P.Y. Henry, B. Howells, B. Isham, P. Jarne, H.A. Jambari, M.
Glaubrecht, M. Kawata, A.V. Korniushin, C. Lively, M. Malaquias, E. Michel, F. Munoz, F. Nijokou, V.
Nuñez, J.P. Pontier, M. Porter, A.M. Ramos, F. Reinhard, T. Smith, M. Stevens, S. Trouve, A. Tsitrone,
M.J. Wallace, D. Wiegel, J. Wise and M. Zeki Yildirim.
Britton, D.K. & McMahon, R.F. (2004) Environmentally and genetically induced shellshape variation in
the freshwater pond snail Physa (Physella) virgata (Gould, 1855). American Malacological
Bulletin, 19, 93–100.
Burch, J.B. (1982) North American freshwater snails: identification keys, generic synonymy,
supplemental notes, glossary, references, index. Walkerana, 1, 1–365.
Burch, J.B. (1989) North American freshwater snails. Malacological Publications, Hamburg, Michigan,
Burch, J.B. & Tottenham, J. (1980) North American freshwater snails: species list, ranges and
illustrations. Walkerana, 1, 1–215.
Burnside, C. (1998) Ecophenotypic variation in shell morphology within the freshwater pond snail genus
Physella (Pulmonata: Basommatophora) and its taxonomic implications. Dissertation, University
of Texas, Arlington, 206 pp.
Cazier, L.D. (1997) Middle Snake River Aquatic Macroinvertebrate and ESA Snail Survey. Annual Report
January 1996 – December 1996. Idaho: U.S. Fish and Wildlife Service. Report nr Section 10
permit PRT#799558. Idaho Power Company, Boise, 17 pp.
Cazier, L.D. (1999a) Bliss Powerplant Tailrace Biological Assessment. Partial annual report June 1999.
Idaho: U.S. Fish and Wildlife Service. Report nr Section 10 permit PRT#799558. Idaho Power
Company, Boise, 4 pp.
Cazier, L.D. (1999b) Middle Snake River Aquatic Macroinvertebrate and ESA Snail Survey: Idaho Power
Company. Responses to FERC Additional Information Request #40 a–c. FERC No. 2777, FERC
No. 2061, FERC No. 1975, FERC No. 2778. Idaho Power Company, Boise, 220 pp.
Cazier, L.D. (1999c) Middle Snake River Aquatic Macroinvertebrate and ESA Snail Survey: Idaho Power
Company. Responses to FERC Additional Information Request #39 a–e. FERC No. 2777, FERC
No. 2061, FERC No. 1975, FERC No. 2778. Idaho Power Company, Boise, 220 pp.
Cazier, L.D. & Myers, R. (1996) Middle Snake River Aquatic Macroinvertebrate and ESA Snail Survey.
Annual report April 1995 – December 1995. Idaho: U.S. Fish and Wildlife Service. Report nr
Section 10 permit PRT#799558. Idaho Power Company, Boise, 26 pp.
Cazier Shinn, D. (2001a) Snake River Aquatic Macroinvertebrate and ESA Snail Survey: 1997. Annual
report January 1997 – December 1997. Idaho: U.S. Fish and Wildlife Service. Report nr Section
10 permit PRT#799558. Idaho Power Company, Boise, 22 pp.
Cazier Shinn, D. (2001b) Snake River Macroinvertebrate Survey: 1998. Annual report January 1998 –
December 1998. Idaho: U.S. Fish and Wildlife Service. Report nr Section 10 permit PRT#799558.
Idaho Power Company, Boise, 24 pp.
Cazier Shinn, D. (2001c) Ecology Studies and Biological Assessment on Snake River ESA Snails: 1999.
Annual report January 1999 – December 1999. Idaho: U.S. Fish and Wildlife Service. Report nr
Section 10 permit PRT#799558. Idaho Power Company, Boise, 40 pp.
Cazier Shinn, D. (2001d) Ecology Studies and Biological Assessment on Snake River ESA Snails: 2000.
Annual report January 2000 – December 2000. Idaho: U.S. Fish and Wildlife Service. Report nr
Section 10 permit PRT#799558. Idaho Power Company, Boise, 52 pp.
Cazier Shinn, D. (2001e) Ecology Studies and Biological Assessment on Snake River ESA Snails: 2000.
Annual report January 2000 – December 2000. Idaho: U.S. Fish and Wildlife Service. Report nr
Section 10 permit PRT#799558. Idaho Power Company, Boise, 41 pp.
Cazier Shinn, D. (2002) Snake River ESA Snail colony Evaluation, Additional Survey and Laboratory
Studies: 2001. Idaho: U.S. Fish and Wildlife Service. Report nr Section 10 permit PRT#799558.
Idaho Power Company, Boise, 22 pp.
Cazier Shinn, D., Foster, A. & Stephenson, M. (2001) Benthic Macroinvertebrates of Hells Canyon Boise:
Idaho Power Company. Technical report nr Appendix E.3.1–8. FERC No. 1971. Idaho Power
Company, Boise, 91 pp.
Chamberlain, R.V. & Jones, D.T. (1929) A Descriptive Catalog of the Molluscs of Utah. Biological Series,
Vol. 1, No. 1. The University of Utah, Salt Lake City, 73 pp.
Crowl, T.A. & Covich, A.P. (1990) Predatorinduced lifehistory shifts in a freshwater snail. Science, 247,
Covitch, A.P., Crowl, T.A., Alexander, J.E. Jr. & Vaughn, C.C. (1994) Predatoravoidance responses in
freshwater decapodgastropod interactions mediated by chemical stimuli. Journal of the North
American Benthological Society, 13, 283–290.
DeWitt, T.J. (1998) Costs and limits of phenotypic plasticity: tests with predatorinduced morphology and
life history in a freshwater snail. Journal of Evolutionary Biology, 11, 465–480.
DeWitt, T.J., Sih, A. & Hucko, J.A. (1999) Trait compensation and conspecialization in a freshwater snail:
size, shape and antipredator behavior. Animal Behavior, 58, 397–407.
DeWitt, T.J., Robinson, B.W. & Sloan Wilson, D. (2000) Functional diversity among predators of a
freshwater snail imposes an adaptive tradeoff for shell morphology. Evolutionary Ecology
Research, 2, 129–148.
Dillon, R.T. Jr. (2000) The ecology of freshwater mollusks. Cambridge University Press, Cambridge,
United Kingdom, 509 pp.
Dillon, R.T. Jr., Wethington, A.R., Rhett, J.M. & Smith, T.P. (2002) Population of the European
freshwater pulmonate Physa acuta are not reproductively isolated from American Physa
heterostropha or Physa integra. Invertebrate Biology, 121, 226–234.
Dillon, R.T. Jr. & Wethington, A.R. (2004) Nochoice mating experiments among six nominal taxa of the
subgenus Physella (Basommatophora: Physidae). Heldia, 6, 69–78.
Dillon, R.T. Jr., Robinson, J.D., Smith, T.P. & Wethington, A.R. (2005) No reproductive isolation
between freshwater pulmonate snails from Physa virgata and P. acuta. The Southwestern
Naturalist. 50, 415–422.
Draparnaud, J. (1805) Histoire Naturelle des Mollusques Terrestres et Fluviatiles de la France. Louis
Colas, Paris, France, 614 pp.
Frest, T.J. (1991) Letter dated 2 June 1991 to Jay Gore, containing a review of Beak and Pentec snail
surveys and studies. US Fish and Wildlife Service, Boise, ID, 16 pp.
Lydeard, C., Holznagel, W.E., Schnare, M.N. & Gutell, R.R. (2000) Phylogenetic analysis of molluscan
mitochondrial LSU rDNA sequences and secondary structures. Molecular Phylogenetics and
Evolution, 15, 83–102.
Remigio, E.A., Lepitzki, D.A.W., Lee, J.S. & Hebert, P.D.N. (2001) Molecular systematic relationships
and evidence for a recent origin of the thermal spring endemic snails Physella johnsoni and
Physella wrighti (Pulmonata: Physidae). Canadian Journal of Zoology, 79, 1941–1950.
Taylor, D.W. (1988) New species of Physa (Gastropoda: Hygrophila) from the western United States.
Malacological Review, 21, 43–78.
Taylor, D.W. (2003) Introduction to Physidae (Gastropoda: Hygrophila) biogeography, classification,
morphology. Revista de Biologia Tropical Vol. 51 Supplemental (1), 1–287.
Te, G.A. (1975) Michigan Physidae, with systematic notes on Physella and Physodon (Basommatophora:
Pulmonata). Malacological Review, 8, 7–30.
Te, G.A. (1978) The systematics of the family Physidae (Basommatophora: Pulmonata). Ph. D.
Dissertation, University of Michigan. 325 pp.
Te, G.A. (1980) New classification system for the family Physidae. Archiv für Molluskenkunde, 110, 179–
Turgeon, D.D., Quinn, J.F., Bogan, A.E., Coan, E.V., Hochberg, F.G., Lyons, W.G., Mikkelsen, P.M.,
Neves, R.J., Roper, C.F.E., Rosenberg, G., Roth, B., Scheltema, A., Thompson, F.G., Vecchione,
M. & Williams, J.D. (1998) Common and scientific names of aquatic invertebrates from the
United States and Canada: mollusks. Special Publications, Vol. 26. American Fisheries Society,
Bethesda, Maryland, 526 pp.
USFWS (1992) Endangered and threatened wildlife and plants; determination of endangered or threatened
status for five aquatic snails in south central Idaho. Federal Register, 57, 59242–59257.
Wethington, A.R. (2004) Phylogeny, taxonomy and evolution of reproductive isolation in Physa
(Pulmonata: Physidae). Ph. D. Dissertation, University of Alabama, Tuscaloosa, 787 pp.
Wethington, A.R. & Guralnick, R. (2004) Are populations of physids from different hot springs distinctive
lineages? American Malacological Bulletin, 19, 135–144.
Wethington, A.R. & Lydeard, C. (2007) A molecular phylogeny of Physidae (Gastropoda:
Basommatophora) based on mitochondrial DNA sequences. Journal of Molluscan Studies, 73,