I’ve had a great time checking this one out, I’m always a biologist at heart. And starfish are really fascinating!
Starfish are echinoderms (e-KY-no-derms) like sea urchins. There are a lot of different types, like there are different types of mammals. They all have a central body with their mouth and gut in it, and arms that help them move. They are predators who catch shellfish to eat. Many biologists now call them sea stars, and they are closely related to brittle stars.
Starfish have hundreds of little feet called tube-feet. They stick out of their arms and help them move, you can see them clearly in this video.
They can move on land too, have a look at this video.
Starfish have two stomachs and they can push their first stomach out through their mouth! This means they can eat something like a clam by pushing their stomach into it’s shell, rather than trying to get it into their mouth. It starts to break down the clam then pulls its stomach back in and passes it to the second stomach. Here is a link for a video of a starfish eating, although you can’t see the stomach. (In fact there are a lot of fun sea star videos, it’s worth looking at some.)
Starfish babies don’t look anything like starfish. They are very tiny (1mm) and float with the algae as zooplankton.
They actually look more like young animals with backbones because they could be cut in half lengthwise. When they get a bit bigger they grow lots of tubes they use to catch even tinier animals. You can see the mouth and stomach in this picture.
Then one side shrinks and the other side starts growing bigger and around, that’s how they start to look like little stars.
There is another way new starfish can grow as well. If they are chopped up, maybe by a big fish, a storm or even by fishermen, the pieces can grow into new starfish. All that’s needed is part of the central body joined to the leg and a new starfish will grow, so you might get two or three starfish out of one!
Starfish have another clever trick, if one of their legs is bitten off they can grow it back.
You can see here that the two legs down the bottom are regrowing.
A starfish has been found in England that should only have five legs, but has eight instead! The biologists who have studied it think it might be conjoined (siamese) twins, it’s now in an aquarium.
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