---
title: "What the sources say about the Planarian | AnimalTracks.wiki"
description: "51 claims from the Planarian profile, each beside the words of the source that backs it."
image: "https://animaltracks.wiki/images/animals/planarian-1.webp"
canonical: "https://animaltracks.wiki/animals/planarian/sources/"
---

# What the sources say about the Planarian (*Schmidtea mediterranea*)

> 51 claims from the Planarian profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [Planarian](https://animaltracks.wiki/animals/planarian/)

## Brand et al. (2026). Stepwise emergence of recombination suppression precedes fissiparous asexuality in the planarian Schmidtea mediterranea. Nature Communications.

https://doi.org/10.1038/s41467-026-74605-9

| The page says | The source says |
| :--- | :--- |
| Fresh water in the western Mediterranean, from the Catalan coast to Tunisia | S. mediterranea has a restricted distribution in the western Mediterranean, with asexual populations on the Catalan coast and the Balearic Islands and sexual populations in Corsica, Sardinia, Sicily, and the Tunisian coast (note: stats.habitat; fresh water: see the tagline claim (gurley-2008 'freshwater planarians')) |
| Hundreds of planarian species live worldwide | the hundreds of planarian species worldwide display a fascinating spectrum of reproductive strategies |
| this one has a restricted distribution in the western Mediterranean | S. mediterranea has a restricted distribution in the western Mediterranean |
| Asexual populations live on the Catalan coast and the Balearic Islands | asexual populations on the Catalan coast and the Balearic Islands |
| Sexual populations live in Corsica, Sardinia, Sicily and the Tunisian coast | sexual populations in Corsica, Sardinia, Sicily, and the Tunisian coast |
| No co-occurrence between the two strains has been reported | No co-occurrence between the two strains has been reported |
| Planarians have a low dispersal ability because they dry out easily | the low dispersal ability of planarians due to their high desiccation susceptibility (note: 'because' is the source's 'due to'; 'dry out easily' renders 'high desiccation susceptibility') |
| Asexual worms reproduce exclusively by fission | The asexual strains reproduce exclusively by fission and subsequent whole-body regeneration and never develop sexual organs |
| followed by whole-body regeneration, and they never develop sexual organs | reproduce exclusively by fission and subsequent whole-body regeneration and never develop sexual organs |
| Sexual worms are hermaphrodites, with both male and female organs, and lay egg capsules | The sexual strains develop hermaphroditic reproductive organs and lay egg capsules containing multiple fertilized zygotes (note: 'with both male and female organs' is the definition of hermaphroditic) |
| Researchers mainly study a clonal lab strain that started from a single animal collected from a fountain in Montjuïc Park, Barcelona, in 1998 | The planarian research community primarily studies a clonal strain (CIW4) originating from a single animal collected from a fountain in Montjuïc Park, Barcelona, Spain, in 1998 |
| the western Mediterranean | S. mediterranea has a restricted distribution in the western Mediterranean |
| Worms that split themselves in two live on the Catalan coast and the Balearic Islands | asexual populations on the Catalan coast and the Balearic Islands (note: asexual strains 'reproduce exclusively by fission') |
| Worms that breed sexually live in Corsica, Sardinia, Sicily and on the Tunisian coast | sexual populations in Corsica, Sardinia, Sicily, and the Tunisian coast |
| In a small part of the world: the western Mediterranean, where it has a restricted distribution | S. mediterranea has a restricted distribution in the western Mediterranean |
| One worm, two ways to breed | this species exists in both asexual and sexual strains |

## Gurley, Rink & Alvarado (2008). β-Catenin Defines Head Versus Tail Identity During Planarian Regeneration and Homeostasis. Science.

https://doi.org/10.1126/science.1150029

| The page says | The source says |
| :--- | :--- |
| whose tail can turn into a head when one gene is switched off | the silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head (note: tagline) |
| Fresh water | freshwater planarians properly regenerate a head or tail (note: stats.habitat, freshwater) |
| Schmidtea mediterranea is a freshwater planarian | freshwater planarians properly regenerate a head or tail (note: 'in the planarian Schmidtea mediterranea' is in the same abstract) |
| When researchers silenced the gene beta-catenin, worms cut at the rear grew a head instead of a tail | RNA interference (RNAi) of beta-catenin or dishevelled causes the inappropriate regeneration of a head instead of a tail at posterior amputations |
| In uncut adult animals, the tail turned into a head | the silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head |
| The authors suggest beta-catenin works as a molecular switch that specifies and maintains head-to-tail identity, during regeneration and in the uncut animal | beta-catenin functions as a molecular switch to specify and maintain anteroposterior identity during regeneration and homeostasis in planarians |
| Researchers shut off a gene called beta-catenin, and worms cut at the back regrew a head where a tail belonged | RNA interference (RNAi) of beta-catenin or dishevelled causes the inappropriate regeneration of a head instead of a tail at posterior amputations |
| Even uncut adult animals had their tails changed into heads | the silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head |
| Yes, in lab tests on this species | We found that in the planarian Schmidtea mediterranea |

## Plass et al. (2018). Cell type atlas and lineage tree of a whole complex animal by single-cell transcriptomics. Science.

https://doi.org/10.1126/science.aaq1723

| The page says | The source says |
| :--- | :--- |
| A freshwater flatworm | Flatworms of the species Schmidtea mediterranea (note: tagline; the 'freshwater planarian' wording is in the cell-atlas/stem-cell literature; flatworm: 'Planarians are flatworms' (plass-2018 quote below)) |
| a type of flatworm | Flatworms of the species Schmidtea mediterranea |
| Scientists have called this species immortal | Flatworms of the species Schmidtea mediterranea are immortal |
| Adults hold a large pool of pluripotent stem cells | adult animals contain a large pool of pluripotent stem cells that continuously differentiate into all adult cell types |
| those cells keep making every adult cell type | continuously differentiate into all adult cell types |
| Not Evaluated | Flatworms of the species Schmidtea mediterranea (note: stats.conservationStatus. Anchors the species name only; the body makes no status claim. GBIF's copy of the IUCN Red List returns category NOT_EVALUATED for Schmidtea mediterranea Benazzi, Baguna, Ballester & del Papa, 1975 (api.gbif.org/v1/species/5892123/iucnRedListCategory, fetched 2026-10-11); an API endpoint can't be cited, and no page found states it, so no IUCN reference is cited (#1227).) |

## Verdesca et al. (2026). Drift of positional identity drives reproductive aging in a long-lived regenerative animal. Current Biology.

https://doi.org/10.1016/j.cub.2026.02.050

| The page says | The source says |
| :--- | :--- |
| A study found that the worms lose fertility as they age | it experiences an age-related loss of fertility, which can be restored through regeneration (note: Verdesca et al. 2026 (ref year)) |
| The problem sits in the female reproductive system, and regeneration can restore it | the source of planarian age-related infertility lies in the female reproductive system (note: 'restores': 'age-related loss of fertility, which can be restored through regeneration' and 'disrupted accessory reproductive structures, which are restored during regeneration') |
| With age, a signaling gradient that sets head-to-tail position shifts toward the tail | the Notum/Wnt signaling gradient, which determines anterior-posterior polarity in planarians, is shifted posteriorly with age |
| tuning it with gene silencing slowed down or sped up the worms' reproductive aging | manipulating this gradient by RNAi was able to slow down or accelerate reproductive aging |

## Pacis et al. (2025). Red Midge Larvae Are an Invertebrate Alternative Diet to Beef Liver for Planarian Husbandry. Biomolecules.

https://doi.org/10.3390/biom15121659

| The page says | The source says |
| :--- | :--- |
| Planarians are carnivores known to feed on living or recently dead invertebrates | planarians are carnivores known to feed on a variety of living or recently dead invertebrates (note: stats.diet; group scope (planarians), not S. mediterranea alone) |
| Planarians in general are carnivores known to feed on living or recently dead invertebrates, including annelids, mollusks, crustaceans, and insect larvae | planarians are carnivores known to feed on a variety of living or recently dead invertebrates, including annelids, mollusks, crustaceans, and insect larvae |
| They extend a cylindrical eating tube, the pharynx, through an opening on the belly | Planarians ingest food via a specialized cylindrical eating tube, the pharynx, which they extend through a ventral opening |
| Its muscles then pull tissue and fluid from the food | The pharyngeal muscles then pull tissue and fluid from the food source via peristalsis |
| They are carnivores | planarians are carnivores (note: 'planarians are carnivores') |
| As a group they are known to eat animals without backbones, alive or recently dead: annelid worms, mollusks, crustaceans and insect larvae | planarians are carnivores known to feed on a variety of living or recently dead invertebrates, including annelids, mollusks, crustaceans, and insect larvae (note: group scope (planarians); 'invertebrates' rendered as 'animals without backbones') |
| Labs typically feed them organic homogenized beef or chicken liver | laboratories typically rely on organic homogenized beef or chicken liver as a food source |

## Sánchez Alvarado (2007). Stem cells and the Planarian Schmidtea mediterranea. Comptes Rendus. Biologies.

https://doi.org/10.1016/j.crvi.2007.05.005

| The page says | The source says |
| :--- | :--- |
| By a 2007 estimate, these stem cells can produce the approximately 40 different cell types found in this animal | a stem cell population capable of producing the approximately 40 different cell types found in this organism (note: 2007 is the year of alvarado-2007, the source of the estimate) |

## Collins et al. (2010). Genome-Wide Analyses Reveal a Role for Peptide Hormones in Planarian Germline Development. PLoS Biology.

https://doi.org/10.1371/journal.pbio.1000509

| The page says | The source says |
| :--- | :--- |
| In one lab study, the sexually mature worms used were about 1 cm long | sexually mature animals (~1 cm in length, unless otherwise specified) |
| About 1 cm long, going by the sexually mature worms of the sexual strain used in one lab study | sexually mature animals (~1 cm in length, unless otherwise specified) (note: 'For all experiments with sexual S. mediterranea, sexually mature animals (~1 cm in length...)') |

## Wenemoser & Reddien (2010). Planarian regeneration involves distinct stem cell responses to wounds and tissue absence. Developmental Biology.

https://doi.org/10.1016/j.ydbio.2010.06.017

| The page says | The source says |
| :--- | :--- |
| Planarians can regenerate from essentially any type of injury | Planarians are able to regenerate from essentially any type of injury |
| Stem cells called neoblasts do the work | Planarian regeneration requires adult stem cells called neoblasts |

## Grohme et al. (2018). The genome of Schmidtea mediterranea and the evolution of core cellular mechanisms. Nature.

https://doi.org/10.1038/nature25473

| The page says | The source says |
| :--- | :--- |
| Planarians regenerate rapidly from tiny tissue pieces | Rapid regeneration from tiny tissue pieces makes planarians a prime model system for regeneration (note: stats.superpower; group scope (planarians)) |
| they regrow rapidly from tiny tissue pieces | Rapid regeneration from tiny tissue pieces makes planarians a prime model system for regeneration |
| transplanting a single neoblast can rescue a worm given a lethal dose of radiation | transplantation of a single neoblast can rescue a lethally irradiated animal (note: group scope (planarians), in the source's introduction) |
| Planarians regrow rapidly from tiny tissue pieces | Rapid regeneration from tiny tissue pieces makes planarians a prime model system for regeneration (note: vibe.reason, same quote as the body) |