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Starfish

Short answer: Sea stars, often called starfish, are echinoderms, related to sea urchins and sand dollars, not fish. Many can regrow lost arms, a process that can take months to a year or more.

Because most of their vital organs extend into the arms, some species can regenerate a whole new animal from a single severed arm, as long as it keeps part of the central disc; a few, such as some Linckia species, can do it from an arm alone. Some also reproduce asexually by splitting. The footage shows sea stars on the seabed and close-ups of their tube feet.

VideoWrite-up2 sources
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What should you know about Starfish?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Sea stars are echinoderms, not fish.

    DD-122-F01 · Write-up · Exhibit A (Not fish)

  2. Many sea stars can regrow lost arms.

    DD-122-F02 · Write-up · Exhibit B (Regrowing arms)

Video transcript: Starfish: A Sea Star Can Regrow a Lost Arm

Starfish also known as sea stars are remarkable creatures capable of regenerating lost body parts. DID YOU KNOW? If starfish loses an arm it can often grow a new one. In some cases a severed arm can even regenerate an entirely new starfish, making them exceptional in the realm of regenerative abilities in the animal kingdom. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 17.6s Reel ·

Video coming soonStarfish · Instagram Reel
Starfish: A Sea Star Can Regrow a Lost Arm Instagram Reel · · 17.6s

The write-up

A sea star can regrow a lost arm. In some species, a severed arm can grow a whole new body.

  1. Exhibit A

    Not fish

    Sea stars are echinoderms, related to sea urchins.

  2. Exhibit B

    Regrowing arms

    Many sea stars can regrow lost arms.

  3. Exhibit C

    It takes time

    Regrowth can take months to a year or more.

  4. Exhibit D

    A whole new animal

    Some species can regrow a whole body from an arm with part of the disc.

  5. Exhibit E

    Splitting

    Some sea stars reproduce asexually by splitting.

Questions people ask about Starfish

What group are sea stars in?

They're related to sea urchins.

Source: Write-up · Exhibit A (Not fish) · NOAA Ocean Service: Is a starfish a fish?

What can many sea stars regrow?

It's a slow process.

Source: Write-up · Exhibit B (Regrowing arms) · NOAA Ocean Service: Is a starfish a fish?; Wikipedia: Starfish

How long can regrowth take?

It depends on the species.

Source: Write-up · Exhibit C (It takes time) · Wikipedia: Starfish

What does an arm usually need to grow a new body?

A few species manage without it.

Source: Write-up · Exhibit D (A whole new animal) · NOAA Ocean Service: Is a starfish a fish?; Wikipedia: Starfish

How else can some sea stars reproduce?

That's asexual reproduction.

Source: Write-up · Exhibit E (Splitting) · Wikipedia: Starfish

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. What group are sea stars in?

    1. Echinoderms
    2. Fish
    3. Mollusks
    4. Crustaceans
    Show the answer

    Answer: A. Echinoderms They're related to sea urchins. Source: Write-up · Exhibit A (Not fish) · NOAA Ocean Service: Is a starfish a fish?

  2. What can many sea stars regrow?

    1. Lost arms
    2. Shells
    3. Fins
    4. Scales
    Show the answer

    Answer: A. Lost arms It's a slow process. Source: Write-up · Exhibit B (Regrowing arms) · NOAA Ocean Service: Is a starfish a fish?; Wikipedia: Starfish

  3. How long can regrowth take?

    1. Months to a year or more
    2. A few hours
    3. A day
    4. Ten years exactly
    Show the answer

    Answer: A. Months to a year or more It depends on the species. Source: Write-up · Exhibit C (It takes time) · Wikipedia: Starfish

  4. What does an arm usually need to grow a new body?

    1. Part of the central disc
    2. A tail
    3. A shell
    4. Nothing
    Show the answer

    Answer: A. Part of the central disc A few species manage without it. Source: Write-up · Exhibit D (A whole new animal) · NOAA Ocean Service: Is a starfish a fish?; Wikipedia: Starfish

  5. How else can some sea stars reproduce?

    1. By splitting
    2. By budding flowers
    3. By spores
    4. They can't
    Show the answer

    Answer: A. By splitting That's asexual reproduction. Source: Write-up · Exhibit E (Splitting) · Wikipedia: Starfish

Cite this case file

Easterling, Marcus. "Starfish." The Detail Department (DetailEnjoyer), case file DD-122, last updated Dec 14, 2023. https://detailenjoyer.com/case/starfish/

Permalink: https://detailenjoyer.com/case/starfish/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-122-F01 → https://detailenjoyer.com/case/starfish/#DD-122-F01