| Range: |
Coastal waters of Florida, Caribbean, and Hawaii |
| Habitat: |
Calm, shallow waters and sandy mud flats |
| Conservation Status: |
Not listed by IUCN |
| Scientific Name: |
Cassiopeia andromeda |
A Jelly by Any Other Name…
Despite their name, upside-down jellies are not made of jelly. And though they're often called "jellyfish," they're not fish. They have no heart, blood, brain, eyes, ears, or gills -- but they are animals!
Head Over Heels
All jellies share some basic body parts. First, there's the bell, the main part of the animal. The bell has a mouth opening, surrounded by four "arms." Inside the bell is a simple stomach and reproductive organs. Fringing the bell is a row of tentacles.
While most jellies drift with ocean currents or propel themselves through the water, upside-down jellies spend most of their time lying on the ocean floor. Like their name implies, these jellies lie upside-down, with their tentacles trailing above them. Because of this, upside-down jellies are often mistaken for anemones, their cousins.
Upside-down jellies are yellow-brown with white or pale spots and streaks. Their arms are brownish and they have frilly tentacles. Adults can grow up to 12 inches in diameter.
Jellies' Bellies
Like all jellies, upside-down jellies spread out their tentacles like a net to catch food -- usually shrimp, crabs, and small fish. And like many jellies, upside-down jellies paralyze their prey with poison. How? When the jellies' tentacles brush against an animal, stinging cells explode and launch barbed stingers into the victim. Ouch!
Besides small aquatic animals, upside-down jellies have another food source: a type of algae which grows within their tentacles. By lying upside-down with their tentacles toward the ocean's surface, the jellies help the algae obtain the sunlight they need to live. And the algae nourish the jellies. This is called a symbiotic relationship -- the jellies help the algae, and the algae help the jellies.
Making Sense of Senses
Since jellies have no brain, eyes, or ears, you might think they can't sense the watery world around them. Far from it!
Though jellies can't see like we can, they can tell light from dark with the help of special light-sensing organs. And receptors on their tentacles and mouth allow jellies to detect smells. Their tentacles and arms are also sensitive to touch -- so jellies can feel when they've trapped an unsuspecting victim. They can also feel when a predator (like an ocean sunfish or leatherback sea turtle) grabs them. When this happens, jellies use their powerful poison to deter the attacker.
Making Little Jellies
They may all look alike to us, but some jellies are female and some are male. An adult female produces eggs and holds them until a male releases sperm into the water. The female gathers up the sperm with her arms and tentacles to fertilize her eggs.
Eggs hatch into larvae, which swim off and then attach to a solid surface. Each larva grows into a polyp, which looks like a little flower. The polyp then proceeds to clone itself, splitting into several new polyps. Each polyp grows into a free-swimming jelly.
Fun Facts
- A jelly's cells replace themselves continually throughout the animal's life. The jelly's body is completely renewed every three weeks!
- Upside-down jellies weren't originally found around the Hawaiian Islands. In the 1940s, ships accidentally introduced the animals to that area.
- This jelly's scientific name, "Cassiopeia," comes from a Greek myth about a beautiful Ethiopian queen of the same name.
Class: Scyphozoa
Order: Rhizostomae
Family: Cassiopeidae
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