Planaria

{{Short description|Genus of flatworms}} {{For|the common name given to many non-parasitic flatworms|Planarian}} {{For|a taxonomic synonym for a genus of snails|Gyraulus}} {{Parenthetical referencing|date=November 2025}} {{Use dmy dates|date=September 2023}} {{Automatic taxobox | image = Planaria torva.jpg | image_caption = ''Planaria torva'' | taxon = Planaria | authority = OF Müller, 1776 }}

'''''Planaria''''' is a genus of planarians in the family Planariidae. Due to its excellent ability to regenerate, species of ''Planaria'' have also been used as model organisms in regeneration studies.<ref>{{Cite journal |last1=Ivankovic |first1=Mario |last2=Haneckova |first2=Radmila |last3=Thommen |first3=Albert |last4=Grohme |first4=Markus A. |last5=Vila-Farré |first5=Miquel |last6=Werner |first6=Steffen |last7=Rink |first7=Jochen C. |year=2019 |title=Model systems for regeneration: planarians |journal=Development |volume=146 |issue=17 |doi=10.1242/dev.167684 |pmid=31511248 |doi-access=free |article-number=dev167684}}</ref> When an individual is cut into pieces, each piece has the ability to regenerate into a fully formed individual.<ref>{{cite web |last=el-Showk |first=Sedeer |date=21 April 2014 |title=Unravelling How Planaria Regenerate |url=http://www.nature.com/scitable/blog/accumulating-glitches/unravelling_regeneration_in_planaria |access-date=26 January 2017 |website=Scitable |publisher=Nature Education}}</ref> When decapitated, they retain their memories.<ref>{{cite web |last=Jacobsen |first=Rowan |date=1 February 2024 |title=Brains Are Not Required When It Comes to Thinking and Solving Problems—Simple Cells Can Do It |url=https://www.scientificamerican.com/article/brains-are-not-required-when-it-comes-to-thinking-and-solving-problems-simple-cells-can-do-it/ |website=Scientific American}}</ref>

== Description == Currently the genus ''Planaria'' is defined as freshwater triclads with oviducts that unite to form a common oviduct without embracing the bursa copulatrix and with an adenodactyl present in the male atrium. The testes occur along the whole body.<ref name="Ball2009">{{cite journal | last1 = Ball | first1 = Ian R. | last2 = Reynoldson | first2 = T. B.| last3 = Warwick | first3 = T. | title = The taxonomy, habitat and distribution of the freshwater triclad ''Planaria torva'' (Platyhelminthes: Turbellaria) in Britain | journal = Journal of Zoology | volume = 157 | issue = 1 | year = 2009 | pages = 99–123 | issn = 0952-8369 | doi = 10.1111/j.1469-7998.1969.tb01691.x}}</ref>

''Planaria'' originally have habitats in dark, murky water which results in such sensitivity (Paskin et al., 2014). They are also sensitive to other stimuli such as chemical gradients, vibration, magnetic and electric fields (Deochand et al., 2018). Their central nervous system includes the anterior (head, brain and eyes) and middle (abdominal trunk and pharynx) (Deochand et al., 2018).

== Diet == The food of ''Planaria'' species includes freshwater gastropods, tubificid worms, and freshwater arthropods, such as isopods of the genus ''Asellus'' and chironomid larvae.<ref name="ReynoldsonSefton1976">{{cite journal | last1 = Reynoldson | first1 = T. B. | last2 = Sefton | first2 = A. D. | title = The food of ''Planaria torva'' (Müller) (Turbellaria-Tricladida), a laboratory and field study | journal = Freshwater Biology | volume = 6 | issue = 4 | year = 1976 | pages = 383–393 | issn = 0046-5070 | doi = 10.1111/j.1365-2427.1976.tb01623.x | bibcode = 1976FrBio...6..383R }}</ref> In the United Kingdom, ''P. torva'' is a successful predator of the invasive New Zealand mud snail (''Potamopyrgus jenkinsi'').<ref name="Reynoldson1979">{{cite journal | last1 = Reynoldson | first1 = T. B. | last2 = Piearce | first2 = Bronwen | title = Predation on snails by three species of triclad and its bearing on the distribution of ''Planaria torva'' in Britain | journal = Journal of Zoology | volume = 189 | issue = 4 | year = 1979 | pages = 459–484 | issn = 0952-8369 | doi = 10.1111/j.1469-7998.1979.tb03974.x}}</ref>

==Species== The following species are recognised in the genus ''Planaria'': {{div col|colwidth=22em}}

*''Planaria adhaerens'' {{small|Korotneff, 1909}} *''Planaria albocingata'' {{small|Korotneff, 1912}} *''Planaria barroisi'' {{small|Whitehouse, 1914}} *''Planaria bicingulata'' {{small|Korotneff, 1912}} *''Planaria chulunginensis'' {{small|Sabussow, 1903}} *''Planaria cincinata'' {{small|Korotneff, 1912}} *''Planaria cinerea'' {{small|Stimpson, 1857}} *''Planaria dagarensis'' {{small|Sabussow, 1903}} *''Planaria debilis'' {{small|Korotneff, 1912}} *''Planaria delineata'' {{small|Korotneff, 1912}} *''Planaria dybouskyi'' {{small|Sabussow, 1903}} *''Planaria flava'' {{small|Delle Chiaje, 1822}} *''Planaria fontana'' {{small|Schrank, 1803}} *''Planaria fuliginosa'' {{small|Leidy, 1851}} *''Planaria fuliginosus'' {{small|Leidy, 1851}} *''Planaria fulvifrons'' {{small|Grube, 1872}} *''Planaria fuscomaculata'' {{small|Korotneff, 1912}} *''Planaria gigas'' {{small|Leuckart, 1828}} *''Planaria grubii'' {{small|Sabussow, 1903}} *''Planaria ignorata'' {{small|Raspail, 1902}} *''Planaria incerta'' {{small|Korotneff, 1912}} *''Planaria kempi'' {{small|Whitehouse, 1913}} *''Planaria lemani'' {{small|(du Plessis, 1874) Graff, 1876}} *''Planaria lucta'' {{small|Korotneff, 1912}} *''Planaria luteola'' {{small|Delle Chiaje, 1822}} *''Planaria macrocephala'' {{small|Fries, 1879}} *''Planaria maculata'' {{small|Dalyell, 1853}} *''Planaria marmorosa'' {{small|Müller, 1776}} *''Planaria melanocerca'' {{small|Korotneff, 1912}} *''Planaria melanopunctata'' {{small|Korotneff, 1912}} *''Planaria melanotorquis'' {{small|Korotneff, 1912}} *''Planaria nesidensis'' {{small|Delle Chiaje, 1822}} *''Planaria onegensis'' {{small|Sabussow, 1903}} *''Planaria punctatum'' {{small|Carus, 1863}} *''Planaria rosea'' {{small|Müller OF, 1773}} *''Planaria rothii'' {{small|Braun, 1884}} *''Planaria sabussowi'' {{small|Korotneff, 1912}} *''Planaria savignyi'' {{small|Leuckart, 1828}} *''Planaria semifasciata'' {{small|Korotneff, 1912}} *''Planaria simplex'' {{small|Woodworth, 1896}} *''Planaria sinensis'' {{small|Stimpson, 1857}} *''Planaria subflava'' {{small|Korotneff, 1912}} *''Planaria torva'' {{small|(Müller OF, 1773)}} *''Planaria tremellaris'' {{small|Grube, 1840}} *''Planaria unionicola'' {{small|Woodworth, 1897}} *''Planaria verrucosa'' {{small|Delle Chiaje, 1829}} *''Planaria wytegrensis'' {{small|Sabussow, 1907}} *''Planaria zeylanica'' {{small|Kelaart, 1858}} {{div col end}}

== Application of planaria in research == These invertebrates are valuable models in toxicology, neuroscience, and pharmacology, offering ethical and cost-effective alternatives to vertebrate testing. Planaria’s simple nervous system, high sensitivity to environmental changes, and well-characterized genome make them particularly useful for studying chemical toxicity, wound healing, and neuroregeneration. Their ease of maintenance in laboratory settings further enhances their appeal for research. In pharmacology and neuroscience, planaria provide a unique opportunity to study the effects of psychoactive compounds, including investigations into drug addiction and withdrawal responses.<ref name=":0">{{Cite book |last1=Raffa |first1=Robert B. |url=https://www.taylorfrancis.com/books/mono/10.1201/9781498713597/planaria-model-drug-action-abuse-robert-raffa |title=Planaria: A Model for Drug Action and Abuse |date=2008-12-03 |publisher=CRC Press |isbn=978-0-429-08997-8 |language=en |doi=10.1201/9781498713597 }}</ref> In drug delivery studies, they can be used to assess the biocompatibility and potential irritancy of pharmaceutical formulations, providing insight into their effects on biological tissues.<ref>{{Cite journal |last1=Shah |first1=Syed Ibrahim |last2=Williams |first2=Adrian C. |last3=Lau |first3=Wing Man |last4=Khutoryanskiy |first4=Vitaliy V. |date=2020-12-01 |title=Planarian toxicity fluorescent assay: A rapid and cheap pre-screening tool for potential skin irritants |url=https://www.sciencedirect.com/science/article/abs/pii/S0887233320305543 |journal=Toxicology in Vitro |volume=69 |article-number=105004 |doi=10.1016/j.tiv.2020.105004 |pmid=33010358 |bibcode=2020ToxVi..6905004S |issn=0887-2333|url-access=subscription }}</ref> Additionally, their remarkable ability to regenerate lost body parts makes them an important model for stem cell research, offering insights into cellular and molecular mechanisms of regeneration.

Using advanced genetic analysis (phylogenomics), scientists confirmed that the family of land planarians, Geoplanidae, is divided into two main sister groups (clades):

One group consists of the subfamilies Bipaliinae and Microplaninae.

The other group consists of Rhynchodeminae and Geoplaninae.<ref>{{cite journal |last1=Fernández |first1=Rosa |last2=Carbayo |first2=Fernando |last3=Mateos |first3=Eduardo |last4=Ángel Fernández-Álvarez |first4=Fernando |last5=Rojo |first5=Iñaki |last6=Salces-Ortiz |first6=Judit |last7=Escudero |first7=Nuria |last8=Benítez-Álvarez |first8=Lisandra |title=Disentangling the evolutionary history of terrestrial planarians through phylogenomics |journal=Molecular Phylogenetics and Evolution |date=September 2025 |volume=210 |article-number=108371 |doi=10.1016/j.ympev.2025.108371 |pmid=40378903 |bibcode=2025MolPE.21008371B |doi-access=free }}</ref>

== References == {{Wikispecies}} {{Reflist}} * {{cite journal |last1=Deochand |first1=N. |last2=Costello |first2=M. S. |last3=Deochand |first3=M. E. |year=2018 |title=Behavioral Research with Planaria |journal=Perspectives on Behavior Science |volume=41 |issue=2 |pages=447–464 |doi=10.1007/s40614-018-00176-w |pmid=31976405 |pmc=6701699 }}

Category:Continenticola Category:Rhabditophora genera