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What the sources say

PlanarianSchmidtea mediterranea

Every figure, record and mechanism on the Planarian profile was written from a source, and this is the working table behind it: 51 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

Profile updated

Source
01

Brand et al. 2026

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

The page saysFresh water in the western Mediterranean, from the Catalan coast to Tunisia
The source saysS. 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 coastNote: stats.habitat; fresh water: see the tagline claim (gurley-2008 'freshwater planarians')
The page saysHundreds of planarian species live worldwide
The source saysthe hundreds of planarian species worldwide display a fascinating spectrum of reproductive strategies
The page saysthis one has a restricted distribution in the western Mediterranean
The source saysS. mediterranea has a restricted distribution in the western Mediterranean
The page saysAsexual populations live on the Catalan coast and the Balearic Islands
The source saysasexual populations on the Catalan coast and the Balearic Islands
The page saysSexual populations live in Corsica, Sardinia, Sicily and the Tunisian coast
The source sayssexual populations in Corsica, Sardinia, Sicily, and the Tunisian coast
The page saysNo co-occurrence between the two strains has been reported
The source saysNo co-occurrence between the two strains has been reported
The page saysPlanarians have a low dispersal ability because they dry out easily
The source saysthe low dispersal ability of planarians due to their high desiccation susceptibilityNote: 'because' is the source's 'due to'; 'dry out easily' renders 'high desiccation susceptibility'
The page saysAsexual worms reproduce exclusively by fission
The source saysThe asexual strains reproduce exclusively by fission and subsequent whole-body regeneration and never develop sexual organs
The page saysfollowed by whole-body regeneration, and they never develop sexual organs
The source saysreproduce exclusively by fission and subsequent whole-body regeneration and never develop sexual organs
The page saysSexual worms are hermaphrodites, with both male and female organs, and lay egg capsules
The source saysThe sexual strains develop hermaphroditic reproductive organs and lay egg capsules containing multiple fertilized zygotesNote: 'with both male and female organs' is the definition of hermaphroditic
The page saysResearchers mainly study a clonal lab strain that started from a single animal collected from a fountain in Montjuïc Park, Barcelona, in 1998
The source saysThe 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 page saysthe western Mediterranean
The source saysS. mediterranea has a restricted distribution in the western Mediterranean
The page saysWorms that split themselves in two live on the Catalan coast and the Balearic Islands
The source saysasexual populations on the Catalan coast and the Balearic IslandsNote: asexual strains 'reproduce exclusively by fission'
The page saysWorms that breed sexually live in Corsica, Sardinia, Sicily and on the Tunisian coast
The source sayssexual populations in Corsica, Sardinia, Sicily, and the Tunisian coast
The page saysIn a small part of the world: the western Mediterranean, where it has a restricted distribution
The source saysS. mediterranea has a restricted distribution in the western Mediterranean
The page saysOne worm, two ways to breed
The source saysthis species exists in both asexual and sexual strains

Source
02

Gurley, Rink & Alvarado 2008

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

The page sayswhose tail can turn into a head when one gene is switched off
The source saysthe silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a headNote: tagline
The page saysFresh water
The source saysfreshwater planarians properly regenerate a head or tailNote: stats.habitat, freshwater
The page saysSchmidtea mediterranea is a freshwater planarian
The source saysfreshwater planarians properly regenerate a head or tailNote: 'in the planarian Schmidtea mediterranea' is in the same abstract
The page saysWhen researchers silenced the gene beta-catenin, worms cut at the rear grew a head instead of a tail
The source saysRNA interference (RNAi) of beta-catenin or dishevelled causes the inappropriate regeneration of a head instead of a tail at posterior amputations
The page saysIn uncut adult animals, the tail turned into a head
The source saysthe silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head
The page saysThe authors suggest beta-catenin works as a molecular switch that specifies and maintains head-to-tail identity, during regeneration and in the uncut animal
The source saysbeta-catenin functions as a molecular switch to specify and maintain anteroposterior identity during regeneration and homeostasis in planarians
The page saysResearchers shut off a gene called beta-catenin, and worms cut at the back regrew a head where a tail belonged
The source saysRNA interference (RNAi) of beta-catenin or dishevelled causes the inappropriate regeneration of a head instead of a tail at posterior amputations
The page saysEven uncut adult animals had their tails changed into heads
The source saysthe silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head
The page saysYes, in lab tests on this species
The source saysWe found that in the planarian Schmidtea mediterranea

Source
03

Plass et al. 2018

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

The page saysA freshwater flatworm
The source saysFlatworms of the species Schmidtea mediterraneaNote: tagline; the 'freshwater planarian' wording is in the cell-atlas/stem-cell literature; flatworm: 'Planarians are flatworms' (plass-2018 quote below)
The page saysa type of flatworm
The source saysFlatworms of the species Schmidtea mediterranea
The page saysScientists have called this species immortal
The source saysFlatworms of the species Schmidtea mediterranea are immortal
The page saysAdults hold a large pool of pluripotent stem cells
The source saysadult animals contain a large pool of pluripotent stem cells that continuously differentiate into all adult cell types
The page saysthose cells keep making every adult cell type
The source sayscontinuously differentiate into all adult cell types
The page saysNot Evaluated
The source saysFlatworms of the species Schmidtea mediterraneaNote: 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).

Source
04

Verdesca et al. 2026

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

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

Source
05

Pacis et al. 2025

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

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

Source
06

Sánchez Alvarado 2007

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

The page saysBy a 2007 estimate, these stem cells can produce the approximately 40 different cell types found in this animal
The source saysa stem cell population capable of producing the approximately 40 different cell types found in this organismNote: 2007 is the year of alvarado-2007, the source of the estimate

Source
07

Collins et al. 2010

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

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

Source
08

Wenemoser & Reddien 2010

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

The page saysPlanarians can regenerate from essentially any type of injury
The source saysPlanarians are able to regenerate from essentially any type of injury
The page saysStem cells called neoblasts do the work
The source saysPlanarian regeneration requires adult stem cells called neoblasts

Source
09

Grohme et al. 2018

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

The page saysPlanarians regenerate rapidly from tiny tissue pieces
The source saysRapid regeneration from tiny tissue pieces makes planarians a prime model system for regenerationNote: stats.superpower; group scope (planarians)
The page saysthey regrow rapidly from tiny tissue pieces
The source saysRapid regeneration from tiny tissue pieces makes planarians a prime model system for regeneration
The page saystransplanting a single neoblast can rescue a worm given a lethal dose of radiation
The source saystransplantation of a single neoblast can rescue a lethally irradiated animalNote: group scope (planarians), in the source's introduction
The page saysPlanarians regrow rapidly from tiny tissue pieces
The source saysRapid regeneration from tiny tissue pieces makes planarians a prime model system for regenerationNote: vibe.reason, same quote as the body

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.