# Jellies (DD-143)

> 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.

- Department: Nature (also Science)
- First published: 2023-12-26
- Last updated: 2023-12-26
- Permalink: https://detailenjoyer.com/case/jellies/
- Original Reel title: Jellies 🪼
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-143-F01**: Jellyfish are the medusa stage of some cnidarians. _(Write-up · Exhibit A (Medusa))_
- **DD-143-F02**: They contract the bell to push water out. _(Write-up · Exhibit B (Jet propulsion))_

## Write-up

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

1. **Medusa**: Jellyfish are the medusa stage of some cnidarians.
2. **Jet propulsion**: They contract the bell to push water out.
3. **No brain**: Jellyfish have no brain, heart or bones.
4. **Mostly water**: They're about 95% water.
5. **Ancient**: Burgessomedusa is about 505 million years old.

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## Reel vs. record

- **Note**: 'Unlike many marine animals that swim by contracting muscles': jellyfish also use muscles; they contract the bell to push out water.
- **Note**: ASR heard an extra 'Jellyfish.' at the end; the captions end at 'environments.', so I left it out.

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

- Duration: 28.8 s · Published: 2023-12-26
- File: https://detailenjoyer.com/assets/videos/C1Ud2ckugpM.mp4

### Transcript

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!

## Questions & answers

**Q: What are jellyfish?**  
A: Related to corals. _(Source: Write-up · Exhibit A (Medusa) · Wikipedia: Jellyfish)_

**Q: How do jellyfish swim?**  
A: Water is pushed out. _(Source: Write-up · Exhibit B (Jet propulsion) · Wikipedia: Jellyfish)_

**Q: Which organ do jellyfish lack?**  
A: They have a nerve net. _(Source: Write-up · Exhibit C (No brain) · Wikipedia: Jellyfish)_

**Q: About how much of a jellyfish is water?**  
A: Almost all. _(Source: Write-up · Exhibit D (Mostly water) · Wikipedia: Jellyfish)_

**Q: How old is Burgessomedusa?**  
A: From the Burgess Shale. _(Source: Write-up · Exhibit E (Ancient) · Wikipedia: Burgessomedusa)_

## Sources

- [Wikipedia: Jellyfish](https://en.wikipedia.org/wiki/Jellyfish)
- [Wikipedia: Burgessomedusa](https://en.wikipedia.org/wiki/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/