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What the sources say

HydraHydra vulgaris

Every figure, record and mechanism on the Hydra profile was written from a source, and this is the working table behind it: 47 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

Auclair et al. 2024

Auclair et al. (2024). Ecotoxicity of a Representative Urban Mixture of Rare Earth Elements to Hydra vulgaris. Toxics.

The page saysSmall prey such as copepods and other zooplankton
The source saysThey feed on small prey, such as copepods and other zooplankton.Note: stats.diet
The page saysHydra is a freshwater polyp, an animal with a tube-shaped body.
The source saysHydras are relatively small organisms (between 2 and 10 mm in length) with a tubular bodyNote: freshwater from the Klymenko line 'small predatory fresh-water polyp' and temperature-2025 'freshwater polyps'
The page saysIt measures between 2 and 10 mm in length
The source saysbetween 2 and 10 mm in length
The page saysHydra feeds on small animals such as copepods and other zooplankton
The source saysThey feed on small prey, such as copepods and other zooplankton.

Source
02

Klymenko & Lutz 2026

Klymenko & Lutz (2026). From Hydra to Humans: Head Activator in Neurogenesis and Neurorepair. Cells.

The page saysA small freshwater polyp
The source saysThe hydra is a small predatory fresh-water polypNote: tagline. The size figure moved out of the tagline: sources disagree (Auclair 2-10 mm, Klymenko up to 30 mm), the body states both.
The page saysa freshwater polyp
The source saysThe hydra is a small predatory fresh-water polyp
The page saysthough the body can reach up to 30 mm
The source saysThe body can reach up to 30 mm in length.
The page saysIts head is ringed by tentacles.
The source saysA hypostome with an oral opening, surrounded by a radially symmetrical crown of tentacles forming the head region.
The page saysThe tentacles are packed with cnidocytes, cells that hold stinging parts and are rich in neurotoxic substances that paralyse prey.
The source saysharbouring stinging organelles (nematocysts) [ 7 ]. The cnidocytes densely populate the tentacle areas of hydra, being enriched in neurotoxic substances, ready for a rapid injection to paralyse different kinds of prey.
The page saysOnce the tentacles have caught a meal, it is moved to the hypostome
The source saysCaptured by the tentacles, the immobilised prey is propelled towards the hypostome.
The page saysIt reproduces mostly without a partner, by budding, which makes genetically identical clones.
The source saysThe reproduction of hydra occurs primarily asexually through budding, resulting in genetically identical clones.

Source
03

Destry, Cochran & Macias-Muñoz 2025

Destry, Cochran & Macias-Muñoz (2025). The effect of temperature on asexual reproduction in Hydra vulgaris. microPublication Biology.

The page saysFresh water
The source saysvulgaris are freshwater polypsNote: stats.habitat
The page saysNot Evaluated
The source saysHydra vulgaris is a model cnidarian used for interdisciplinary studies in biologyNote: stats.conservationStatus. GBIF's copy of the Red List has no category for Hydra vulgaris and the prefetch found no assessment DOI (Crossref searches for synonyms returned HTTP 429), so no IUCN reference is cited. The quote names the species only. Precedent: great-scallop.
The page saysIt belongs to the phylum Cnidaria, the group that also holds jellyfish, sea anemones and corals.
The source saysbelong to the phylum Cnidaria, which encompasses jellyfish, sea anemones, and corals
The page saysthe hypostome, the mouth opening
The source saysPhotograph of a Hydra polyp with tentacles, hypostome (mouth opening)Note: Figure 1 caption of the same paper.
The page saysWarmth boosts budding.
The source saysOur findings indicate that Hydra populations exhibit increased growth through asexual budding at higher temperatures.
The page saysBy the end of one lab test, an average of 45 polyps were budding at 25 degrees Celsius, against 4 at 15 degrees
The source saysBy the end of experimental weeks, an average of 45 polyps were budding at 25°C compared to 4 at 15°C.
The page saysIt can reproduce sexually, but it also buds.
The source saysH. vulgaris are also capable of reproducing both sexually and asexually by budding.
The page saysUnder favorable conditions, a bud forms in the lower section of the body
The source saysUnder favorable conditions, a bud develops in the lower section of the H. vulgaris body.
The page sayspasses through 10 stages of growth and tentacle formation, then detaches as a new polyp
The source saysThe bud proceeds through 10 stages of growth and tentacle formation, then detaches from the parent polyp

Source
04

Schaible et al. 2015

Schaible et al. (2015). Constant mortality and fertility over age in Hydra. Proceedings of the National Academy of Sciences.

The page sayswhose death rate in lab studies stayed flat as it got older
The source sayshave extremely low, constant rates of mortalityNote: tagline; two closely related Hydra species, lab cohorts
The page saysevery animal that breeds repeatedly would see its death rate rise and its fertility fall with age after maturity
The source saysSenescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding.Note: 'scientists thought' keeps the source's 'was thought to be inevitable'.
The page saysA 2015 study put that to the test on 2,256 Hydra from two closely related species.
The source says2,256 Hydra from two closely related species in two laboratories in 12 cohortsNote: Year 2015 is the schaible-2015 reference year (PNAS, first published online 7 December 2015 per the MPIDR press release).
The page saysSpread across 12 groups in two labs, they had extremely low, constant rates of mortality.
The source saysin two laboratories in 12 cohorts, with cohort age ranging from 0 to more than 41 y, have extremely low, constant rates of mortalityNote: Reviewer cut the 0-41 year range: it is cohort age, not the age of any individual polyp, and read as a 41-year-old hydra.
The page saysThe researchers say features such as a high proportion of stem cells and rapid cell turnover may make that flat death rate possible.
The source saysA high proportion of stem cells, constant and rapid cell turnover, few cell types, a simple body plan, and the fact that the germ line is not segregated from the soma are characteristics of Hydra that may make nonsenescence feasible.

Source
05

Max Planck Institute for Demographic Research, press release

Forever young. Max Planck Institute for Demographic Research, press release.

The page saysReplaces all of its cells within four weeks
The source saysas Hydra replaces all of their cells within only four weeksNote: stats.superpower
The page saysIn a lab in Rostock, Germany, researchers cared for about 1,800 polyps over almost ten years
The source saysFor almost ten years they have cared for of about 1,800 of the Hydras in a laboratory in the basement of the institute in Rostock.Note: Rostock, Germany is the dateline: 'Rostock, Germany.'
The page sayseach in its own small glass dish at a constant 18 degrees Celsius
The source saysEach polyp lives in its own small glass dish exposed to a natural day-and-night cycle in special cabinets that are kept at a constant temperature of 18 degrees Celsius.
The page saysfed three times a week
The source saysThree times a week they are fed exactly the same amount of food.
The page saysTheir yearly chance of dying stayed at a low 0.6 percent.
The source saysFor Hydra, however, it remains constant at a low 0.6 percent.Note: 'it' is the probability of dying within one year, per the previous sentence.
The page saysFor humans, it reaches levels as high as 50 percent at advanced ages.
The source saysFor humans the probability of dying within one year is reaching levels as high as 50 percent for advanced ages.
The page saysIts stem cells can develop into any part of the body.
The source saysStem cells are capable of developing into any part of the body at any time.
The page saysHydra replaces all of its cells within four weeks
The source saysas Hydra replaces all of their cells within only four weeks
The page saysit regularly expels cells that mutations have changed
The source saysit regularly and quickly expels all cells that have been changed genetically by mutations
The page saysIt can completely replace body parts that are damaged or lost, and it can fully regenerate if its body is almost completely destroyed.
The source saysHydra are capable of completely replacing parts of the body that are damaged or are somehow lost. It can even fully regenerate if its body is destroyed almost completely
The page saysA hydra replaces all of its cells within four weeks, and in the lab its death rate stayed flat as it aged.
The source saysas Hydra replaces all of their cells within only four weeksNote: vibe.reason; the rest of the sentence restates body claims: Spread across 12 groups in two labs, they had extremely low, constant rates of m

Source
06

Martı́nez 1998

Martı́nez (1998). Mortality Patterns Suggest Lack of Senescence in Hydra. Experimental Gerontology.

The page saysfollowed three groups of hydra for four years and tracked deaths and reproduction
The source saysmortality and reproductive rates for three hydra cohorts have been analyzed for a period of four yearsNote: 1998 is the martinez-1998 reference year.
The page saysDeath rates stayed extremely low and reproduction showed no apparent sign of falling.
The source saysmortality rates have remained extremely low and there are no apparent signs of decline in reproductive rates

Source
07

Sahm et al. 2024

Sahm et al. (2024). Hydra has mammal-like mutation rates facilitating fast adaptation despite its nonaging phenotype. Genome Research.

The page saysIn the wild, Hydra's average life span is counted in weeks rather than years, because of high extrinsic mortality
The source saysIn the wild, due to a high extrinsic mortality, Hydra ’s average life span is counted in weeks rather than in yearsNote: Genus scope. Also Schaible 2015: 'the short life expectancy of Hydra in the wild'. Lifespan claim. 'because' is the source's own 'due to'.
The page sayswhich is the death rate from outside causes
The source saysdue to a high extrinsic mortalityNote: Definition of the term; no quote defines it. Cut if the reviewer prefers.
The page saysThe lab is a kind place, though.
The source saysThe nonsenescent phenotype is observable only under benign laboratory conditionsNote: Framing sentence; 'only' is the source's.

Source
08

Schenkelaars et al. 2020

Schenkelaars et al. (2020). The polymorphism of Hydra microsatellite sequences provides strain-specific signatures. PLOS ONE.

The page saysHydra strains collected from around the world
The source saysHydra strains collected worldwideNote: stats.habitat; the body names the range with the same claim. Scope: genus strains, no finer geographic range is stated in any cached source (2 audit searches and 3 Europe PMC queries found none).
The page saysResearchers have collected Hydra strains from around the world.
The source saysHydra strains collected worldwide

Source
09

Dupre & Yuste 2017

Dupre & Yuste (2017). Non-overlapping Neural Networks in Hydra vulgaris. Current Biology.

The page saysIt was long described as a simple nerve net.
The source saysthe nervous system of Hydra is traditionally described as a simple nerve net
The page saysresearchers used calcium imaging to record the activity of essentially all of its neurons
The source saysusing calcium imaging of genetically engineered animals to measure the activity of essentially all of its neuronsNote: 2017 is the dupre-2017 reference year.
The page saysfound a series of networks that do not overlap, each tied to a specific behavior
The source saysa series of functional networks that are anatomically non-overlapping and are associated with specific behaviors
The page saysOne network is active when the body contracts lengthwise, another when it stretches in response to light.
The source saysactivated selectively during longitudinal contractions, elongations in response to light, and radial contractions

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.