25 Interesting Facts About Starfish

1. The starfish is a star-shaped marine invertebrate. There are around 2,000 known species of starfish. They are present in all the world’s oceans, and live on the ocean floor. 
2. Starfish are not related to fish. They belong to a group of animals known as echinoderms. It is the reason that they are also called sea stars. The closest relatives of starfish are sea urchins and sand dollars.
3. The purple sea star was one of the first recognized keystone species necessary to keep balance in their habitat. The absence of this starfish in its habitat can increase the population of mussels, resulting in the extinction of all other species. (Source)
4. Most of the starfish species have five arms. But few species can have 10, 20, or even up to 40 limbs.
5. Starfish have varying colors. They are present in brown, pink, red, yellow, purple, or orange color of various intensities. These colors and their shades depend on species and environmental conditions. Many species can also change color via camouflage. (Source)
6. There are numerous tube feet on the underside of each starfish’s arm. These tiny tube feet are hollow and full of water. They assist the animal in adopting various movements underwater. (Source)

   

   There are several tube feet in starfish's arms

   
   
7. Starfish can reproduce sexually as well as asexually. These have sexual organs in each arm. Male and female starfish release sperms and eggs into the water during breeding seasons for sexual reproduction. They meet in the process known as spawning. Asexual reproduction happens if a starfish losses its arm and part of the central disk. This arm can change into a new starfish. (Source)
8. A study shows that starfish can intentionally shed their limbs in case of a consistent hot environment. It is necessary to prevent overheating of their central disk. The core temperature of 35 C can be fatal for sea stars. (Source)
9. Sea stars can regenerate their lost arms. Few species need the existence of a central body for regeneration, while others can regenerate just from a portion of a limb. They can do so thanks to the presence of all vital organs in their limbs.
10. The crown-of-thorns starfish is known for its hunting of corals and can cause damage to coral reefs in a few areas. But the guard crabs living in these corals can act as the natural protector of coral reefs by pinching the starfish successfully. (Source)
11. Northern pacific sea star is native to the coasts of China and adjacent countries. But it has proved to be one of the worst invasive species in Australia, where it is reducing the population of native species, especially shellfish. (Source)
12. Starfish have no blood in their bodies. They use seawater, a water vascular system, and tube feet to move their circulatory system.
13. Most starfish are carnivores that eat clams, oysters, mussels, etc. They have two stomachs (cardiac and pyloric stomach). They use the cardiac stomach to digest the prey outside their body, while the pyloric stomach digests the food inside the body. This procedure enables them to eat prey larger than their stomach.
14. Starfish have been present on earth for hundreds of millions of years. The oldest known ancestor of starfish, discovered in Morocco, is 480 million years old. (Source)
15. Starfish are not suitable for human consumption. Several sea stars are poisonous to humans and can cause mild to severe toxicity in the human body. (Source)
16. Few starfish species are hermaphrodites (male and female simultaneously) and can sexually reproduce without mating. In some species, juvenile sea stars become large after eating their siblings. (Source)
17. Starfish have several predators, including sharks, manta rays, and Alaskan king crabs. Larger starfish may also eat smaller ones in the absence of any other food source.
18. Starfish employ various defensive techniques to escape their predators. Tube feet assist them in escaping slow-moving predators while they can conceal themselves by burrowing into the sea sand. Releasing their arms, camouflage, and unpleasant skin also protect starfish against predators. (Source) 
19. The common starfish is sensitive to pollution. It acts as a bioindicator of heavy metals in a marine environment. (Source) 

    

    Starfish are bioindicator in marine environment

    
    
20. Starfish have a strange ability to expel foreign objects from their bodies through the skin at the tip of their arms. (Source)
21. Starfish are without a brain and a central nervous system. However, it has a decentralized nervous system, and individual body parts act independently according to the requirement. (Source)
22. Starfish can live for 35 years in the wild on average. However, their lifespan in captivity is five to ten years. 
23. Starfish have eyespots at the tip of each arm. They cannot detect colors and can only distinguish between light and dark. They are unable to see fast-moving objects. They have 360 degrees field of vision around themselves. (Source)
24. The sunflower star is the largest and heaviest starfish. It has an arm length of nearly 40 inches and can weigh up to 11 pounds. They can also move very quickly at 40 inches per minute. (Source)
25. Most starfish species can remain alive for 3 to 5 minutes out of water. But few species can survive for hours outside water by holding their breath. One species, the ochre star, can remain alive for 28 hours out of water.