Book 6, Question 38
Why Does a Starfish Have Five Arms?
A sea star is not a fish. Most kinds have five arms around a center. Tiny tube feet line the underside. Leave live sea stars in the water.
From the book
Page from A Million Whys Book 6
More fun facts
- Most sea stars have five arms, but some kinds have 10, 20 or even 40.
- Sea stars have fivefold symmetry, so their bodies can be split into five matching parts.
- Scientists prefer the name sea star, because these animals are not fish.
- Each arm is lined with rows of tiny tube feet.
- A recent study suggests a sea star's body is basically one big head.
- The five-way shape of sea stars has long puzzled scientists who study how animals evolved.
Sources: NOAA Ocean Service, Scientific American, National Geographic, Smithsonian Magazine
Questions kids ask
Do all sea stars have five arms?
No. Some kinds have 10, 20 or even 40 arms.