When we think of the word fish, most people imagine animals that live in water, have fins, and can swim. But sometimes, the names of animals can be tricky. Two animals with “fish” in their name are the starfish and the jellyfish. Are they really fish? Let’s find out in simple words.
What is a Fish?
A fish is an animal that lives in water and has a backbone. Most fish have:
- Gills to breathe underwater
- Fins to swim
- Scales covering their body
Fish are part of a group called vertebrates, which means they have a spine or backbone inside their body. Common examples of fish are salmon, goldfish, and tuna.
Starfish: Is It a Fish?
Despite its name, a starfish is not a fish. Here is why:
- No backbone: Starfish do not have a spine. Instead, they have a hard outer shell called an exoskeleton.
- Body shape: They have a star-like shape with five arms (sometimes more).
- Movement: Starfish move using tiny tube feet, not fins.
- Breathing: Starfish do not have gills. They breathe through tiny structures on their arms.
Because of these reasons, scientists say that starfish are echinoderms, not fish. Echinoderms are a group of animals that live in the ocean, like sea urchins and sand dollars.
Jellyfish: Is It a Fish?
What about the jellyfish? Surprisingly, it is also not a fish. Here’s why:
- No backbone: Jellyfish are soft and squishy and do not have a spine.
- Body structure: They have a bell-shaped body with tentacles.
- Movement: Jellyfish drift in the water using the current and some can slowly pulse their body to move.
- Breathing: Jellyfish do not have gills. They absorb oxygen directly from water through their thin skin.
Because of this, jellyfish are called cnidarians, a group of animals that includes sea anemones and corals.
Why Are They Called “Fish”?
The word “fish” in starfish and jellyfish can be confusing. Long ago, people named animals based on where they live or how they look. Since starfish and jellyfish live in water and move like fish, people added “fish” to their names. Today, we know that their biology is very different from real fish.
Differences Between Starfish, Jellyfish, and Fish
FeatureStarfishJellyfishReal FishBackboneNoNoYesFinsNoNoYesBreathingTube feet skinSkinGillsBody ShapeStar-shapedBell-shapedStreamlinedGroupEchinodermCnidarianVertebrate
This table makes it clear that neither starfish nor jellyfish is a real fish.
Fun Facts About Starfish and Jellyfish
- Starfish: They can regrow lost arms. Some species can even grow a new starfish from one arm.
- Jellyfish: Some jellyfish are almost immortal. The species Turritopsis dohrnii can go back to its early stage and start its life cycle again.
- Habitat: Both animals live in oceans, but starfish prefer the sea floor while jellyfish float in open water.
- Diet: Starfish eat shellfish like clams, while jellyfish catch small animals with their tentacles.
How to Tell the Difference Between Real Fish and These “Fish”
If you want to know if an animal is a true fish:
- Check for a backbone. Fish have one; starfish and jellyfish do not.
- Look for fins. Fish swim with fins.
- Look at the skin. Fish have scales.
- Breathing method. Fish use gills to get oxygen from water.
If an animal fails these tests, it is not a fish, no matter what its name says.
Why Names Can Be Confusing
Animal names are sometimes confusing because they were given long ago. People used the word “fish” for anything that lived in water. Today, scientists use the animal’s classification to know the truth. This is why starfish are echinoderms and jellyfish are cnidarians.
FAQs
Q1: Are starfish poisonous?
A1: Most starfish are not poisonous, but some species can be harmful if eaten.
Q2: Can jellyfish sting humans?
A2: Yes, some jellyfish have stings that can hurt humans. Always be careful in the ocean.
Q3: Are starfish and jellyfish endangered?
A3: Some species are at risk because of pollution and climate change, but many are still common in the ocean.
Q4: Can starfish swim like fish?
A4: No, starfish cannot swim. They crawl slowly using their tube feet.
Q5: Do jellyfish have brains?
A5: No, jellyfish do not have a brain or heart. They have a simple nerve network to sense their surroundings.
Conclusion
To answer the question: Which of these is a fish: starfish or jellyfish?
The answer is neither. Both animals live in water and have “fish” in their names, but they are very different from real fish. Starfish are echinoderms, and jellyfish are cnidarians. Understanding their differences helps us appreciate the amazing variety of life in our oceans.