Planaria

For the common name given to many non-parasitic flatworms, see Planarian.

For a taxonomic synonym for a genus of snails, see Gyraulus.

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.^[1] When an individual is cut into pieces, each piece has the ability to regenerate into a fully formed individual.^[2] When decapitated, they retain their memories.^[3]

Planaria
Planaria torva
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Order:	Tricladida
Family:	Planariidae
Genus:	Planaria OF Müller, 1776

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.^[4]

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.^[5] In the United Kingdom, P. torva is a successful predator of the invasive New Zealand mud snail (Potamopyrgus jenkinsi).^[6]

Species

The following species are recognised in the genus Planaria:

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

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.^[7] 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.^[8] 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.