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Jellies

Short answer: Jellyfish are the free-swimming medusa stage of certain cnidarians. They move by contracting their bell-shaped bodies, which pushes water out and drives them forward; many species also gain efficiency from vortices formed as the bell relaxes.

Jellyfish have no brain, heart or bones, and they're about 95% water. Fossils show jellyfish-like animals at least 500 million years ago, including Burgessomedusa from the Burgess Shale, about 505 million years old, described in 2023. The footage shows jellyfish drifting in blue water, with the presenter.

VideoWrite-up2 sources
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What should you know about Jellies?

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

  1. Jellyfish are the medusa stage of some cnidarians.

    DD-143-F01 · Write-up · Exhibit A (Medusa)

  2. They contract the bell to push water out.

    DD-143-F02 · Write-up · Exhibit B (Jet propulsion)

Video transcript: Jellies: Jellyfish Have Been Around for Over 500 Million Years

Jellyfish are fascinating creatures known for their otherworldly appearance. DID YOU KNOW? Unlike many marine animals that swim by contracting muscles, jellyfish use a process called jet propulsion. They open and close their bell-shaped bodies, expelling water to propel themselves forward. Jellyfish have been around for a very long time. Fossil evidence suggests that jellyfish have been in existence for at least 500 million years, making them one of the oldest living organisms on Earth. Despite their ancient origins, jellyfish continue to thrive in various marine environments. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 28.8s Reel ·

Video coming soonJellies · Instagram Reel
Jellies: Jellyfish Have Been Around for Over 500 Million Years Instagram Reel · · 28.8s

The write-up

Jellyfish have been around for over 500 million years. They swim by squeezing water out of their bells.

  1. Exhibit A

    Medusa

    Jellyfish are the medusa stage of some cnidarians.

  2. Exhibit B

    Jet propulsion

    They contract the bell to push water out.

  3. Exhibit C

    No brain

    Jellyfish have no brain, heart or bones.

  4. Exhibit D

    Mostly water

    They're about 95% water.

  5. Exhibit E

    Ancient

    Burgessomedusa is about 505 million years old.

Questions people ask about Jellies

What are jellyfish?

Related to corals.

Source: Write-up · Exhibit A (Medusa) · Wikipedia: Jellyfish

How do jellyfish swim?

Water is pushed out.

Source: Write-up · Exhibit B (Jet propulsion) · Wikipedia: Jellyfish

Which organ do jellyfish lack?

They have a nerve net.

Source: Write-up · Exhibit C (No brain) · Wikipedia: Jellyfish

About how much of a jellyfish is water?

Almost all.

Source: Write-up · Exhibit D (Mostly water) · Wikipedia: Jellyfish

How old is Burgessomedusa?

From the Burgess Shale.

Source: Write-up · Exhibit E (Ancient) · Wikipedia: Burgessomedusa

Test Your Knowledge

All quizzes →

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

  1. What are jellyfish?

    1. The medusa stage of some cnidarians
    2. Fish
    3. Mollusks
    4. Plants
    Show the answer

    Answer: A. The medusa stage of some cnidarians Related to corals. Source: Write-up · Exhibit A (Medusa) · Wikipedia: Jellyfish

  2. How do jellyfish swim?

    1. By contracting the bell
    2. With fins
    3. By walking
    4. With a tail
    Show the answer

    Answer: A. By contracting the bell Water is pushed out. Source: Write-up · Exhibit B (Jet propulsion) · Wikipedia: Jellyfish

  3. Which organ do jellyfish lack?

    1. A brain
    2. A mouth
    3. Tentacles
    4. Cells
    Show the answer

    Answer: A. A brain They have a nerve net. Source: Write-up · Exhibit C (No brain) · Wikipedia: Jellyfish

  4. About how much of a jellyfish is water?

    1. 95%
    2. 10%
    3. 50%
    4. 0%
    Show the answer

    Answer: A. 95% Almost all. Source: Write-up · Exhibit D (Mostly water) · Wikipedia: Jellyfish

  5. How old is Burgessomedusa?

    1. About 505 million years
    2. About 5,000 years
    3. About 5 million years
    4. About 5 billion years
    Show the answer

    Answer: A. About 505 million years From the Burgess Shale. Source: Write-up · Exhibit E (Ancient) · Wikipedia: Burgessomedusa

Cite this case file

Easterling, Marcus. "Jellies." The Detail Department (DetailEnjoyer), case file DD-143, last updated Dec 26, 2023. https://detailenjoyer.com/case/jellies/

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

Markdown version

Cite a single fact by its ID, for example DD-143-F01 → https://detailenjoyer.com/case/jellies/#DD-143-F01