Physella acuta, also known as European physa, tadpole snail, bladder snail, or acute bladder snail, is a species of small, air-breathing freshwater snail of the family Physidae. It originates from North America and was first described in France in 1805 by Jacques Philippe Raymond Draparnaud.[4]
The shell of P. acuta is sinistral (left-coiling), as is typical of physids. It reaches up to 12 mm in length and forms a high spiral with a pointed apex. The mantle is blue to dark grey with golden spots and often visible through the thin shell. Like other physids, P. acuta presents an unique set of muscles called the physid musculature, which allow the snail to rapidly twist its shell as a defense mechanism.[5]
P. acuta is invasive on all continents except Antarctica and is considered "the world's most cosmopolitan freshwater gastropod".[6] Its first introduction outside North America likely occurred through the 18th century cotton trade to Europe, while later spread mainly happened through the aquarium trade.[7][8] In invaded habitats, P. acuta frequently outcompetes native freshwater snails.[7]
The species often arrives in aquariums through ornamental plants and can become a "pest snail" due to its rapid reproduction. However, a balanced population of P. acuta can help clean up organic leftovers in aquariums and avoid bacterial growth.[9]
Taxonomy and nomenclature
Physella acuta was first described in France in 1805 by Jacques Philippe Raymond Draparnaud, originally as Physa acuta.[2] The specific epithetacuta is Latin for "sharp" and refers to the species' pointed shell.[10] In 1817 Thomas Say independently described the same species in Pennsylvania, naming it Physa heterostropha.[11] Until the beginning of the 21st century this and several other newly described species were considered distinct from each other until molecular and reproductive studies revealed them to be synonyms of P. acuta.[7]
The species was originally placed in the genus Physa but was later reassigned to Physella according to molecular phylogenetic studies.[12] This taxonomy is accepted by MolluscaBase, the mollusk-oriented branch of WoRMS.[3] However, other authors and databases may use synonyms such as Physa acuta or Haitia acuta.[13], because while the family Physidae is well supported, the structure of the subfamily Physinae is still unclear as of 2025. Debates include the taxonomic relationships between its members as well as the definition and number of physinine genera and species, all of which also affect the identity of P. acuta.[14] This taxonomic uncertainty is partly due to vague descriptions in early works, which could apply to multiple taxa,[15] and to the generalist nature of physids, including P. acuta, which lead to morphological plasticity and rapid evolution.[14]
Description
External anatomy
Shell
Shell of Physella acuta
Like other members of the family Physidae, the shell of P. acuta lacks an operculum, a "trapdoor" that closes the aperture (shell opening), and is sinistral. Sinistral shells are left-coiling, meaning that when held with the aperture facing the observer and the spire (coiled part of the shell) pointing upward, the aperture is on the left-hand side.[16] The shell is thin and reaches up to 12 mm in length.[17] It forms a high spiral of four to five whorls (complete revolutions) which take about two-thirds of the shell length and end in a pointed apex (tip). Sutures (grooves between the whorls) are impressed and clearly visible. The aperture is ear-shaped and takes about three-quarters of the total shell height. Both the columella (central pillar within the shell) and the apertural lip (the opening's margin) are white. The shell surface is smooth, thin to the point of being slightly transparent, and ranges in colour from pale horn to brownish yellow.[18][19]
According to the U.S. Geological Survey (USGS), the species presents a high diversity of shell shapes which led to numerous false species descriptions before the onset of molecular phylogenetic studies.[20] Shells of P. acuta can be especially difficult to distinguish from those of Physella gyrina and Stenophysa marmorata if live specimens are not available. Typically, P. gyrina has a shorter spire with shallower sutures and a larger shell which can exceed 13 mm in length.[18][21] The shell of S. marmorata is thinner and less globous.[22]
Soft parts
Physella acuta on an aquarium glass.
The body of P. acuta is very variable in colour, which can range from blue to dark grey. The top mantle (tissue covering the visceral mass of the animal) has golden spots often visible under the thin shell.[20] Finger-like lobes extend from the mantle on both sides of the body, smaller than in other physids such as Physa fontinalis or Stenophysa marmorata. They can act as an accessory gill by extracting additional oxygen from the environment and help detect predators through the touch-sensitive tissue.[23][24] The tentacles are grey and follow the build of other members within the family Physidae: cylindrical and slender, almost transparent, with small black eyes at the base.[18] These pit eyes only distinguish between light and dark.[25] The foot is narrow and ends in a pointed tail, as is also typical of the family. The mouth edge is large and flared. The body is an important point of distinction from P. gyrina and S. marmorata:P. gyrina has whitish spots over its whole dark grey body including the tentacles.[18] The mantle extensions of S. marmorata are not digitated and extend broadly over the sides of the shell and this species has a black stripe running through the middle of the tail.[22]
Internal anatomy
Musculature
Like all members of the family Physidae, P. acuta has a specialised set of muscles called the physid musculature. These muscles are unique among gastropods and allow the snail to rapidly twist its shell in clockwise rotations of up to 120°. This shell-shaking movement is an important depense against predators. The main components of the physid musculature are the muscle sensu stricto and the fan muscle. They provide the twisting force, serve as a base for the movement, anchor the shell to the body, and help return the shell to its original position afterwards.[5]
Reproductive organs
P. acuta is a simultaneous hermaphrodite, meaning it has both male and female reproductive organs functioning at the same time. In Physidae, the male organs are important for taxonomic identification and consist of prepuce, penis sheath, and penis.[26] The prepuce is a tube that releases or receives sperm from outside and, in the case of P. acuta, includes a small, lentil-shaped gland. It is wider and twice as long as the muscular penis sheath.[27][28] The penis is white and 160 - 180 μm in length.[29] It is elongated and narrow along most of its length but ends in a wider, rounded tip.[30] The penis musculature consists of circular muscles in both the outer and inner layers, while the intermediate layer has only longitudinal muscles. Together with molecular phylogenetic data, this musculature pattern can be used to distinguish major groups within the superorder Hygrophila.[29] The female organs are less frequently described in detail. They consist of a convoluted oviduct (which transports the eggs to the outside), a nidamental gland (which secretes the egg capsule), and a vagina connected to the spermathecal duct (which receives sperm) opening to the outside.[27]
Distribution and habitat
Origin and introduction history
P. acuta was originally thought to be native to the Mediterranean region. However, reproductive isolation experiments[31] and molecular genetic studies[32] revealed it to be the same species as the North American Physella heterostropha and Physa integra. Comparative anatomy, fossil evidence, and phylogenetic data also support a North American origin, specifically within the United States. However, its exact native range within the country remains debated, with hypotheses for both eastern and western origins.[4][7]
The timing and pathway of P. acuta's first arrival in Europe are also uncertain. One hypothesis links it back to eastern U.S. populations via the 18th century cotton trade,[7] although earlier or natural introductions have also been proposed.[15] Once within Europe, its initial spread was likely facilitated by man-made canals.[15][33]
Current distribution
P. acuta is widely dispersed across the globe, largely due to the aquarium trade.[8] It is an invasive species which can be found on all continents except Antarctica and is considered "the world's most cosmopolitan freshwater gastropod".[6]
Ecology
Habitat
Physella acuta can survive in eutrophic habitats such as lakes with excess algal growth.
P. acuta can occupy a variety of freshwater habitats as well as habitats varying widely in water availability.[20] It tolerates harsh environmental conditions such as polluted and eutrophic (oxygen-deprived) waters.[34] It has been reported in lakes, reservoirs, ponds, streams, ditches, as well as artificial sites such as sewage drains and irrigation systems.[35][36]
Feeding habits
P. acuta is a scraper feeder. It uses its radula (a tongue-like structure covered in small chitinous teeth) to scrape green algae, diatoms, and aquatic plants from the surface.[37]
Reproduction
P. acuta is a self-compatiblehermaphrodite, meaning it is capable of both outcrossing (reproduction with another individual) and self-fertilisation.[38] In natural populations, reproduction occurs mainly by outcrossing, but self-fertilisation rates still remain between 10 - 30% and can increase as an adaptation strategy when mates are scarce.[39][40]
Adults lay 50 - 100 eggs per week for up to a year after reaching sexual maturity.[20] Eggs are deposited in elongate gelatinous sacs and hatch after 15 - 20 days. Individuals reach sexual maturity after 17 - 18 months.[41]
Anentome helena is often kept in aquariums to control populations of smaller snail species such as Physella acuta.
Predation
P. acuta is predated by a variety of animals, including water bugs,[51]marsh fly larvae,[52]crayfish,[53]leeches,[24] and various fish species.[54][55] To a lesser degree, it is also prey to the invasive carnivorous snail Anentome helena.[49] Anti-predator behaviours include shell-shaking (rapid shell movements) and crawling to or above the waterline,[24][25] as well as burying into the sediment,[55] leaping (shell-shaking combined with detachment from the surface, causing the snail to jerk away),[24][56] clamping to the substrate, and detatching to float up to the surface.[57]
Parasitism
P. acuta is a potential intermediate host for parasites of both native wildlife and humans[7]. Due to its cosmopolitan distribution and invasive capacity, it has the potential to significantly influence the distribution of parasites within freshwater ecosystems.[58] Reported infections include the turtle parasites Krefftascaris spp. and spirorchiids,[58][59] the bird parasite Cotylurus cornutus[59], and the rat parasite Euparyphium albuferensis,[60] although infection prevalence within invasive P. acuta populations is often low.[7] Experiments exposing P. acuta to the human parasites Hypoderaeum conoideum and Trichobilharzia regenti yielded no successful infections.[61] This is consistent with the enemy-release hypothesis, the observation that non-native species carry fewer parasites outside their native range.[62] The species was once directly linked to a human illness when Echinostoma, which cause echinostomiasis, were recorded in P. acuta individuals from public parks in Rio de Janeiro, Brazil.[63]
Aquarium trade
Physella acuta is often called a "pest snail" in freshwater fishkeeping. It is usually introduced with ornamental plants or decoration. A single introduced individual can be enough to establish a population due to the snail's capacity to self-fertilise and to reproduce quickly. An excessive reproduction of P. acuta may result from an excessive supply of food in the aquarium, for example in the form of overfeeding, feeding poorly digestible food (undigested parts are excreted and become available to the snails), and infrequent water changes. However, a balanced population of P. acuta in the aquarium can help clean up organic leftovers and prevent bacterial growth.[9] They are peaceful snails which will not attack healthy plants and can feed other tank inhabitants.[64]
1 2 Draparnaud J.-P.-R. 1805. Histoire naturelle des mollusques terrestres et fluviatiles de la France. Ouvrage posthume. Avec XIII planches. pp. [1-9], j-viij [= 1-8], 1-134, [Plates 1-13]. Paris, Montpellier. (Plassan, Renaud).
1 2 Duggan, Ian C. (November 2010). "The freshwater aquarium trade as a vector for incidental invertebrate fauna". Biological Invasions. 12 (11): 3757–3770. Bibcode:2010BiInv..12.3757D. doi:10.1007/s10530-010-9768-x. ISSN1573-1464.(subscription may be required or content may be available in libraries)
↑ 1817. Say, T. "Conchology." in W. Nicholson (ed.). American Edition of the British Encyclopedia or Dictionary of Arts and Sciences, Comprising an Accurate and Popular View of the Present Improved State of Human Knowledge. First Edition. Samuel A. Mitchell and Horace Ames, Philadelphia, Pennsylvania. Vol. 2 + 4 plates. No pagination.
↑ Miyahira, I. C., Gonçalves, I. C. B., Lacerda, L. E. M., Ximenes, R. F., & Santos, S. B. (2021). The introduction of Physa acuta (Gastropoda: Physidae) on Ilha Grande, Southeast Brazil, from initial stages to an established population. Brazilian Journal of Biology, 83, e243801.
1 2 3 Vinarski, Maxim V. (April 2017). "The history of an invasion: phases of the explosive spread of the physid snail Physella acuta through Europe, Transcaucasia and Central Asia". Biological Invasions. 19 (4): 1299–1314. Bibcode:2017BiInv..19.1299V. doi:10.1007/s10530-016-1339-3. ISSN1573-1464. S2CID254292899.(subscription may be required or content may be available in libraries)
↑ Hammond, George; Burch, John B. "Physidae". Animal Diversity Web. Retrieved 2025-08-17.
↑ Koopman, K. Remon; Collas, Frank P. L.; van der Velde, Gerard; Verberk, Wilco C. E. P. (2016-01-01). "Oxygen can limit heat tolerance in freshwater gastropods: differences between gill and lung breathers". Hydrobiologia. 763 (1): 301–312. doi:10.1007/s10750-015-2386-y. hdl:2066/151227. ISSN1573-5117.
1 2 3 4 Krupski, Adam; Karasek, Tomasz; Koperski, Paweł (February 2018). "Differences between two physid species (Gastropoda: Physidae) in antipredator behaviour induced by leeches". Journal of Molluscan Studies. 84 (1): 96–102. doi:10.1093/mollus/eyx049. ISSN0260-1230.
1 2 Paraense, W. L., & Pointier, J. P. (2003). Physa acuta Draparnaud, 1805 (Gastropoda: Physidae): a study of topotypic specimens. Memórias do Instituto Oswaldo Cruz, 98, 513-517.
↑ Wethington, A. R. (2004) Family Physidae. A supplement to the workbook accompanying the FMCS Freshwater Identification Workshop, University of Alabama, Tuscaloosa, 24 pp.
↑ Cope, Neisha J.; Winterbourn, Michael J. (March 2004). "Competitive interactions between two successful molluscan invaders of freshwaters: an experimental study". Aquatic Ecology. 38 (1): 83–91. doi:10.1023/B:AECO.0000021018.20945.9d. ISSN1573-5125.(subscription may be required or content may be available in libraries)
1 2 3 Früh, Denise; Haase, Peter; Stoll, Stefan (January 2017). "Temperature drives asymmetric competition between alien and indigenous freshwater snail species, Physa acuta and Physa fontinalis". Aquatic Sciences. 79 (1): 187–195. Bibcode:2017AqSci..79..187F. doi:10.1007/s00027-016-0489-9. ISSN1420-9055.(subscription may be required or content may be available in libraries)
↑ Karmakar, Rupsha, Pranesh, Paul, De, Sujeeta, Mondal, Debjit, & Aditya, Gautam (2021). Temperature-dependent interaction between an invasive and a native freshwater gastropod: a competitive edge for the invader. Biological Letters, 55(1-2), 17-29.
1 2 3 Paul, Pranesh; Das, Rajat; Nandy, Gargi; Aditya, Gautam (March 2025). "Preferring what others avoid: differences in the vulnerability of freshwater snails to the exotic and native predators". Hydrobiologia. 852 (5): 1385–1396. Bibcode:2025HyBio.852.1385P. doi:10.1007/s10750-022-05062-w. ISSN1573-5117.(subscription may be required or content may be available in libraries)
↑ McDonnell, R. J., Knutson, L., Vala, J. C., Abercrombie, J., Henry, P. Y., & Gormally, M. J. (2005). Direct evidence of predation by aquatic, predatory Sciomyzidae (Diptera, Acalyptrata) on freshwater snails from natural populations.
1 2 Barragán-Sáenz, Francisco Adrián; Sánchez-Nava, Petra; Hernández-Gallegos, Oswaldo; Salgado-Maldonado, Guillermo (October 2009). "Larval stages of trematodes in gastropods from Lake Chicnahuapan, State of Mexico, Mexico". Parasitology Research. 105 (4): 1163–1167. doi:10.1007/s00436-009-1536-4. ISSN1432-1955. PMID19568770.
↑ Esteban, J.G.; Toledo, R.; Sánchez, L.; Muñoz-Antolí, C. (November 1997). "Life-cycle of Euparyphium albuferensis n. sp. (Trematoda: Echinostomatidae) from rats in Spain". Systematic Parasitology. 38 (3): 211–219. doi:10.1023/A:1005894813021. ISSN1573-5192.
↑ Moreira, L. D. L., Silva, E. F. D., Gomes, S. R., Mattos, A. C. D., Sousa, A. K. P. D., Silva, A. B. P. D., ... & Thiengo, S. C. (2024). Public parks in the city of Rio de Janeiro, southeast Brazil, and the risk of parasitosis transmission by freshwater gastropods. Anais da Academia Brasileira de Ciências, 96(2), e20230707.
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