Planaria Explained

Planaria is a genus of planarians in the family Planariidae.Due to its excellent ability to regenerate, species of Planaria has 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]

Various species of Planaria have been widely used as model invertebrate organisms in pharmacological research, in particular in the studies of the drugs of abuse.^[4] They were also proposed as models in toxicological research.^[5]

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.^[6]

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.^[7] In the United Kingdom, P. torva is a successful predator of the invasive New Zealand mud snail (Potamopyrgus jenkinsi).^[8]

Species

The following species are recognised in the genus Planaria:

• Planaria adhaerens
• Planaria albocingata
• Planaria barroisi
• Planaria bicingulata
• Planaria chulunginensis
• Planaria cincinata
• Planaria cinerea
• Planaria dagarensis
• Planaria debilis
• Planaria delineata
• Planaria dybouskyi
• Planaria flava
• Planaria fontana
• Planaria fuliginosa
• Planaria fuliginosus
• Planaria fulvifrons
• Planaria fuscomaculata
• Planaria gigas
• Planaria grubii
• Planaria ignorata
• Planaria incerta
• Planaria kempi
• Planaria lemani
• Planaria lucta
• Planaria luteola
• Planaria macrocephala
• Planaria maculata
• Planaria marmorosa
• Planaria melanocerca
• Planaria melanopunctata
• Planaria melanotorquis
• Planaria nesidensis
• Planaria onegensis
• Planaria punctatum
• Planaria rosea
• Planaria rothii
• Planaria sabussowi
• Planaria savignyi
• Planaria semifasciata
• Planaria simplex
• Planaria sinensis
• Planaria subflava
• Planaria torva
• Planaria tremellaris
• Planaria unionicola
• Planaria verrucosa
• Planaria wytegrensis
• Planaria zeylanica

References

• Deochand, N., Costello, M. S., & Deochand, M. E. (2018). Behavioral Research with Planaria. Perspectives on behavior science, 41(2), 447–464. https://doi.org/10.1007/s40614-018-00176-w

Notes and References

1. Web site: Model systems for regeneration: planarians . 10.1242/dev.167684 . free . 2023-01-21 . journals.biologists.com.
2. Web site: Unravelling How Planaria Regenerate. Sedeer el-Showk. 26 January 2017.
3. https://www.scientificamerican.com/article/brains-are-not-required-when-it-comes-to-thinking-and-solving-problems-simple-cells-can-do-it/
4. Book: Planaria: A Model for Drug Action and Abuse . 2008-12-03 . CRC Press . 978-0-429-08997-8 . en . 10.1201/9781498713597. Raffa . Robert B. .
5. Shah . Syed Ibrahim . Williams . Adrian C. . Lau . Wing Man . Khutoryanskiy . Vitaliy V. . 2020-12-01 . Planarian toxicity fluorescent assay: A rapid and cheap pre-screening tool for potential skin irritants . Toxicology in Vitro . en . 69 . 105004 . 10.1016/j.tiv.2020.105004 . 33010358 . 222159871 . 0887-2333.
6. Ball . Ian R. . Reynoldson . T. B.. Warwick . T. . The taxonomy, habitat and distribution of the freshwater triclad Planaria torva (Platyhelminthes: Turbellaria) in Britain . Journal of Zoology . 157 . 1 . 2009 . 99–123 . 0952-8369 . 10.1111/j.1469-7998.1969.tb01691.x.
7. Reynoldson . T. B. . Sefton . A. D. . The food of Planaria torva (Müller) (Turbellaria-Tricladida), a laboratory and field study . Freshwater Biology . 6 . 4 . 1976 . 383–393 . 0046-5070 . 10.1111/j.1365-2427.1976.tb01623.x.
8. Reynoldson . T. B. . Piearce . Bronwen . Predation on snails by three species of triclad and its bearing on the distribution of Planaria torva in Britain . Journal of Zoology . 189 . 4 . 1979 . 459–484 . 0952-8369 . 10.1111/j.1469-7998.1979.tb03974.x.