Fun fact 10 of 10
10. Starfish have no brain and no blood
Starfish live without a brain and without blood. Instead of blood, they pump seawater through their bodies, and many species can regenerate a lost arm.
Seawater instead of blood
Inside, the starfish has a network of canals filled with seawater, called the water vascular system. Water enters through a small plate on the back, circulates through the arms carrying nutrients, and fills the tube feet on the underside. It is with them that the starfish moves and clings to rocks.
There is also no central brain. Control sits in a ring of nerves around the mouth, with a nerve running along each arm. At the tip of each arm is a light-sensitive spot that works like a simple eye and helps the animal orient itself.
Regeneration is its most famous trick. If it loses an arm to a predator, the starfish can grow a new one in its place, which takes months. In some species, a detached arm that carries part of the central body can even turn into a whole starfish.
It also has a curious way of eating: many species can push their own stomach out of their body. By wrapping around a shellfish, the starfish forces the shells open just a little, pushes its stomach through the gap, and starts digesting the food right there.
Did you know? The starfish is not a fish: it belongs to the echinoderm group, the same as sea urchins and sea cucumbers. There are about 2 thousand species, in all oceans, from shallow waters to the great depths.
The 10 fun facts in this list
- The octopus has three hearts and blue blood
- Sharks are older than trees
- The giraffe has the same seven neck vertebrae as you
- Dolphins sleep with half of their brain at a time
- The owl cannot turn its head 360 degrees, but comes close
- Cats cannot taste sweetness
- In seahorses, it is the male who gets pregnant
- Flamingos are not born pink
- The blue whale's heart weighs about 180 kilograms
- The starfish has no brain and no blood
Sources of this information: Live Science, Smithsonian Ocean and NOAA (octopus, starfish and seahorse); Live Science and Discover Wildlife (sharks and trees); Johns Hopkins University and Science journal, 2013 (owls); PLoS Genetics, 2005 (cats and sweetness); Royal Ontario Museum and PNAS, 2019 (blue whale).
