What are sea stars?

Sea stars are animals!

• They are not fish! Although commonly called starfish, these animals are not fish. So we prefer to call them sea stars.
  
  
• Sea stars have five-part symmetry
  Many common stars we see have five arms. Although some may have more arms, or less arms.
  
  
• Sea stars need sea water Instead of blood, a sea star uses sea water to pump its body parts and move. Water inside the sea star may also help it keep cool at low tide. So please don't remove sea stars from the water for too long.
  
  
  • Let's NOT take the group photo with each person holding the sea star in the hand. Let's put the sea stars in the water and get close to them for the group photo.
  • See also why we should not pick up sea stars on the wild shores of singapore blog.
    
    
• Stars are fragile! When stressed, a star may purposely drop off an arm. Just like a gekko drops its tail. So don't carry the sea star by the tip of an arm. The star might think a predator is chomping on it and will purposely drop off the arm.
  
  
• Parts of a sea star When showing this, make sure the sea star is always immersed in seawater, either in a pool or in your pot.
  
  • The sea star has grooves under its arms where tube feet emerge. The tubefeet help it to move, to gather food.
  • The mouth is in the middle of all the feet.
    

• It is NOT true that all sea stars can regenerate from a broken piece of their arms.
  
  
  • You won't get two sea stars when an arm of a sea star is separated. So please don't purposely mutilate sea stars!! VERY FEW stars can generate a new animal from a broken off arm. In MOST STARS the broken off bit dies.
    
    
  • Some sea stars can regenerate lost arms. But this takes time and resources. Some species take up to a year to replace a lost limb. In the meantime, the sea star is probably disadvantaged.
    
    
  • If the central disk is damaged, the sea star may die.
    
    
• Can I take this dead sea star home? All the sea stars that you see are probably alive.
  
  You are unlikely to come across a skeleton of a sea star. Dead sea stars disintegrate quickly and do not leave behind whole skeletons.
  
  A live sea star also has moving tube feet. When removed from the water, however, sea stars will retract their tube feet and may appear dead.
  
  Those dead sea stars you see sold as souvenirs were taken alive and dried. What a cruel way to die!
  
  
• Aren't sea stars bad for reefs? Don't they eat up all the hard corals? The Crown-of-Thorns sea star (Acanthaster planci) is notorious for decimating reefs. This sea star eats the polyps of hard corals leaving behind dead white skeleton.
  • These sea stars are only a danger to reefs when there is a population explosion of them. Such a situation is generally is believed to be due to an imbalance in the natural system. For example, when their predators are overharvested.
  • When there are low numbers of this sea star, they do not cause massive damage.
  • This sea star has not been encountered on our shores.