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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe largest starfish ever documented by a formal record is the brisingid sea star Midgardia xandaros, measured at 1.38 metres (4 feet 6 inches) from tip to tip. Guinness World Records says that specimen was collected in the Gulf of Mexico in 1968. That is a span record, not proof that Midgardia is the heaviest or most massive sea star.
A precise, evidence-backed ranking of the ten largest species is not currently possible from comparable published measurements. The strongest additional evidence concerns the sunflower sea star, Pycnopodia helianthoides, whose reported maximum varies by measurement and source: up to 1 metre in arm span, up to 130 centimetres in diameter, and up to 5 kilograms in mass. The species below are therefore a documented selection of very large sea stars, not an exact worldwide top-ten order.
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Why “largest starfish” needs a definition
“Starfish” and “sea star” are common names for marine echinoderms in the class Asteroidea. Aquariums, museums and conservation agencies often prefer “sea star,” but both terms refer to the same animal group. There are close to 2,000 described sea star species, and their bodies range from delicate, narrow-armed forms to broad animals with many thick arms.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesSize can be reported in several incompatible ways. A thin-armed species may have the greatest distance between opposite arm tips while carrying relatively little tissue. A broad-bodied species may have a smaller tip-to-tip span but a greater mass. A source may also report disc diameter, overall diameter or arm span without using those terms identically.
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| Measure | What it tells you | Why it cannot be substituted for another measure |
|---|---|---|
| Tip-to-tip span | Distance from the end of one arm to the opposite arm tip | Favors species with long, narrow arms and does not indicate body mass |
| Diameter | Overall width across the animal, as defined by the source | Some sources use “diameter” for a relaxed body while others describe an extended animal |
| Arm span | Width across the extended arms | May be effectively equivalent to diameter in one account but not in another |
| Mass | Weight of the animal | Changes with feeding, reproductive condition, water content and measurement method |
For that reason, a responsible comparison keeps the measurement beside every number. It should never turn a 1.38-metre span into a claim that the same species is the world’s heaviest sea star.
The confirmed span record: Midgardia xandaros
What Guinness actually records
Guinness World Records identifies the brisingid sea star Midgardia xandaros as the largest starfish in its record entry. The recorded specimen measured 1.38 metres (4 feet 6 inches) from tip to tip. It was collected in the Gulf of Mexico in 1968 by the Texas A&M University research vessel Alaminos.
This is a single documented specimen and a specific record category: maximum tip-to-tip span. The entry does not establish a ranked list of ten species, nor does it compare the animal’s mass with that of broad-bodied sea stars. Brisingid sea stars typically have long, slender arms, a body plan that can produce an exceptional span without making the animal proportionally heavy.
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- The 1.38-metre figure is a measured specimen, not a stated average adult size.
- The collection year was 1968; it should not be presented as a recent population survey.
- “Largest” in this record means the greatest documented span, not greatest diameter, volume or mass.
- No named-person quotation about Midgardia xandaros accompanies the record, so claims about its behavior or typical size require separate species evidence.
The sunflower sea star: the largest broad-bodied contender
Different authorities report different maxima
The sunflower sea star, Pycnopodia helianthoides, is widely described as one of the largest living sea stars. Aquarium of the Pacific reports an arm span of up to 1 metre and a mass of up to 5 kilograms. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) reported in its 2025 assessment that adults can reach up to 130 centimetres in diameter. NOAA’s status review describes the species as exceeding 1 metre from tip to tip and places it among the largest sea stars.
Those figures are not contradictory if they are kept with their definitions and sources. A 1-metre arm span, a 130-centimetre diameter and a 5-kilogram mass describe different attributes or use different maximum observations. They should not be merged into one invented “official” size.
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Why its many arms matter
Sunflower sea stars can have as many as 24 arms. Their flexible bodies and numerous tube feet allow them to spread over a large area while moving across the seafloor. The NOAA review reproduces biologist Walter K. Fisher’s 1928 description: “When under ‘full sail,’ with its thousands of tube-feet lashing back and forth, it is an impressive animal, and its numerous cushions of tenacious pedicellariae and the wide expanse of its flexible body make it a formidable engine of destruction.”
The description reflects the animal’s predatory design rather than a ranking claim. Sunflower stars use their mobility and broad reach to overtake prey that a slower or narrower-armed sea star might not catch.
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Documented large sea stars, without a false ranking
The table below includes only candidates for which the cited material supplies a concrete size figure. It is deliberately not numbered from first to third: the measurements are not equivalent, and the available evidence does not provide comparable maxima for ten species.
| Species or common name | Reported maximum | Measurement and provenance | What can safely be concluded |
|---|---|---|---|
| Midgardia xandaros | 1.38 m (4 ft 6 in) | Tip to tip; Guinness World Records specimen collected in the Gulf of Mexico in 1968 | Formal documented span record |
| Pycnopodia helianthoides (sunflower sea star) | Up to 1 m span; up to 130 cm diameter; up to 5 kg mass | Arm span and mass from Aquarium of the Pacific; adult diameter and arm count from COSEWIC’s 2025 assessment; NOAA describes over 1 m tip to tip | Among the largest broad-bodied sea stars; figures are source-specific |
| Giant-spined sea star | Up to 60 cm diameter | UCSB Long Term Ecological Research field guide, 2005 | A substantial size reported in a field guide, but not a verified worldwide maximum |
| Sunflower sea star (museum estimate) | Up to 90 cm diameter | University of Puget Sound Museum of Natural History species account | A separate source-specific estimate that should not replace the larger figures above |
The two sunflower-star diameter figures illustrate why source attribution matters. One account gives up to 90 centimetres, while COSEWIC reports adults up to 130 centimetres. They may reflect different samples, definitions or records; the evidence does not justify choosing one as a universal limit without explaining the source.
Why there is no reliable “top ten” list yet
A true top-ten ranking would require the same kind of measurement for at least ten distinct species, together with a clear provenance for each maximum. The available material does not meet that standard. Some species names appear in general discussions of very large sea stars, but their returned evidence does not provide a comparable, authoritative maximum.
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Names that need better verification
- Thromidia gigas is often mentioned in discussions of large sea stars, but no comparable maximum measurement is established in the cited material here.
- Crown-of-thorns sea stars are conspicuous and can have many arms, yet the available evidence does not supply a directly comparable worldwide maximum for this article.
- Mithrodia clavigera also surfaced as a possible large species, but a verified maximum with matching measurement and provenance is not established.
Leaving these species out of a ranked table is more accurate than assigning numbers based on unsourced web descriptions. A future comparison would need original taxonomic descriptions, museum specimen records and authoritative species accounts, while separating maximum observed specimens from typical adult size.
Where the biggest sea stars live and what they eat
Sunflower stars in the northeast Pacific
Pycnopodia helianthoides occupies the eastern Pacific. NOAA’s status review places its range from Alaska to at least Baja California. It is a fast-moving predator of rocky and soft-bottom communities, where its many arms and tube feet help it locate and engulf prey.
The National Park Service lists sea urchins, snails, clams, sea cucumbers, crabs and other sea stars among its prey. Eating sea urchins is especially important ecologically: by reducing dense urchin populations, sunflower stars can help preserve kelp habitat. This role means that the species matters beyond its impressive dimensions.
Large size is not the same as danger to people
Sea stars are invertebrate predators, not aggressive animals that pursue swimmers. Their tube feet provide movement and attachment, while tiny structures called pedicellariae help handle food and surface material. A large specimen should still be left undisturbed. Lifting a sea star out of water, exposing it to heat or allowing it to dry can cause serious physiological stress, even when the animal appears intact.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Conservation: the biggest species is also a species in trouble
Sea star wasting syndrome
The National Park Service reports that sea star wasting syndrome began spreading rapidly in the northeast Pacific in 2013. The event affected 22 sea star species, and sunflower stars nearly disappeared from California. Symptoms can include tissue lesions, loss of body structure and rapid disintegration, although causes and severity vary among outbreaks and locations.
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A missing sunflower star is not merely a loss of a large, photogenic animal. Because the species consumes sea urchins and other invertebrates, its decline can alter predator-prey relationships and place additional pressure on kelp ecosystems.
Canada’s 2025 designation
COSEWIC designated the sunflower sea star as Endangered in Canada in May 2025. That is a Canadian conservation assessment; it is not a claim that the species has one identical legal status in every country across its range. Readers should distinguish a national designation from a global classification.
How to read size claims in aquarium and wildlife articles
General educational pages sometimes state that the largest sea stars reach about 3 feet in diameter. The National Aquarium uses that broad figure while species-specific sources give different maxima for sunflower stars. A general statement can be useful orientation, but it should not be treated as a measurement of every large species.
When two pages disagree, check four questions before deciding that one is wrong:
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- Are both pages measuring the same thing—span, diameter or mass?
- Is the number a single record specimen, a maximum observed value or a typical adult size?
- Does the source identify the species and explain how the measurement was taken?
- Is the date and geographic context clear?
Applying those checks explains why the Guinness figure remains the formal span record while sunflower-star sources can report a heavier, broader animal without overturning it.
What this means for readers who keep aquariums
The largest sea stars discussed here are wild marine animals with specialized diets, substantial space requirements and conservation concerns. Their size does not make them suitable additions to a home aquarium. In particular, a sunflower star’s predatory behavior, need for stable seawater conditions and dependence on live prey make casual ownership inappropriate.
For observation, choose a reputable public aquarium or a protected tide-pool site and follow local rules. Do not remove sea stars from the shore, transport them in containers or return them to the water after prolonged handling. Wildlife agencies and aquariums provide safer ways to learn about these animals than collecting them.
Quick Recap
Key takeaways
- Midgardia xandaros holds the documented Guinness span record at 1.38 metres tip to tip, based on a 1968 Gulf of Mexico specimen.
- The sunflower sea star is one of the largest broad-bodied species, with source-reported maxima of up to 1 metre span, 130 centimetres diameter and 5 kilograms mass.
- Those numbers measure different attributes and cannot be collapsed into one universal ranking.
- Only a few species have comparable, well-proven figures in the available authoritative material, so an exact top ten would overstate the evidence.
- Sunflower stars are important northeast Pacific predators and have suffered severe declines associated with sea star wasting syndrome; Canada designated them Endangered in 2025.
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