Masters of regeneration - Planaria
Shrewsbury, MA
Planaria are a species of flatworm that typically live in freshwater marine environments with a diet of shrimp, snails, and protozoa. There are around 1,500 species of planaria. Planaria are ciliated, meaning they have small cilia, hairlike structures, located all around their body, which they use to move. Unlike other flatworm species, planaria do not live off of a host organism. Instead, they eat by wrapping themselves around their prey and extending their pharynx to eat. Planarians’ eye spots are primitive, meaning they do not actually see, but they detect light. Planaria do not have lungs or gills- instead they take in oxygen and let out carbon dioxide through their cell membranes.
However, what makes these worms special is their amazing ability to regenerate. Humans can regenerate too, but only up to a certain extent, for example, a wound healing. Planaria, on the other hand, can regenerate when cut into as many as 279 pieces!. This is because planaria contain a special type of stem cell called neoblasts. Neoblasts are located everywhere in the planaria except for the brain and pharynx, and they make up around twenty percent of all the cells in the planaria. When one thinks of human stem cells, one tends to think of multipotent stem cells, which are only capable of turning into certain types of cells, and, as such, can only contribute to reconstructing certain tissues. In contrast, neoblasts are pluripotent stem cells, meaning they have the potential to turn into any type of cell in the body. Neoblasts act as an internal repair system and are the key to planarians' unique regeneration ability.
The first step in the regeneration process is that the wound where the planaria was injured gets healed, and the exposed tissues are covered up. Then, in order for the planaria to regenerate its lost organs, the neoblasts migrate to the wound area to begin the regeneration process. But how do these neoblasts know where to go? Well, present inside the DNA of the neoblasts are genes called position control genes or PCG’s, which act like a GPS system, guiding and directing the neoblasts where to go and what to become. Then, in the final step of the regeneration, the neoblasts form a white bump called a blastema, and begin dividing and becoming different types of cells to regrow the lost tissue.
Works Cited
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Friar, Greta. “How One Worm Can Rebuild Its Whole Body | Whitehead Institute.” Whitehead Institute of MIT, 31 Oct. 2022, https://wi.mit.edu/news/how-one-worm-can-rebuild-its-whole-body. Accessed 20 Aug. 2026.
“Planarian | EBSCO.” EBSCO Information Services, Inc. | Www.Ebsco.Com, 2022, https://www.ebsco.com/research-starters/zoology/planarian. Accessed 20 Aug. 2026.
“Possible Key to Regeneration Found in Planaria’s Origins.” Stowers Institute for Medical Research, https://www.stowers.org/news/feb-13-2017. Accessed 20 Aug. 2026.
Reddien, Peter W., and Alejandro Sánchez Alvarado. “FUNDAMENTALS of PLANARIAN REGENERATION.” Annual Review of Cell and Developmental Biology, vol. 20, no. 1, Nov. 2004, pp. 725–757, https://www.sdbonline.org/sites/2012Course/annurev_cellbio.pdf, 10.1146/annurev.cellbio.20.010403.095114. Accessed 20 Aug. 2026.
Rossant, Janet. “Planaria: Genes for Regeneration.” eLife, eLife Sciences Publications, Ltd, 15 Apr. 2014, https://elifesciences.org/articles/02517. Accessed 20 Aug. 2026.
Scanza, Rachel. “Where the Wild Things Are: Planarian Flatworms.” Stowers Institute for Medical Research, 13 Dec. 2023, https://www.stowers.org/news/where-the-wild-things-are-planarian-flatworms. Accessed 20 Aug. 2026.
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