Sea stars have many weird and wonderful adaptations – including some unusual internal systems. Click on any of the labels in this interactive to view short video clips or s to learn more.
Sea stars have many weird and wonderful adaptations – including some unusual internal systems. Click on any of the labels in this interactive to view short video clips or s to learn more.
Don’t forget to flip the sea star over and see what’s on top – the dorsal view!
Sea stars are invertebrates so they don’t have a backbone, but they do have a skeleton beneath their skin. This endoskeleton is made up of a complex network of hard bony plates made of calcium carbonate and held together by strong flexible tissues.
Sea stars have a very unusual circulatory system. They do not pump blood around their bodies. Instead, they use seawater and a complex water vascular system to keep things moving. Their tube feet, also used for movement, are an important part of this circulatory system. Sea stars have hundreds of tube feet on their underside.
A sea star has 2 stomachs, the cardiac stomach and the pyloric stomach. It can push the cardiac stomach out of its mouth, in the centre of its underside, to engulf prey or insert it into prey (between 2 shells, for example). The stomach then secretes a powerful digestive enzyme to break down the prey.
When the cardiac stomach comes back into the body, the food in it is transferred to the pyloric stomach.
Sea stars don’t use gills or lungs to breathe. They rely on diffusion across surfaces in their body. For example, most oxygen is taken up from water that passes over their tube feet and papulae or skin gills. Skin gills are small projections near the base of the spines, usually on the topside.
They move relatively slow so we wouldnt necessarily see them swimming or see them moving around. But certainly if you were to watch them for long enough you would see they are very mobile, and they move around using special structures called tube feet, which are like little tentacles with little suckers on the end of them, and an individual starfish will have 2 or 3 hundred of those. So it’s got these little tentacles, which are on its underside, which it uses to hold on to the rock wall or the wharf piling or whatever and move around in a co-ordinated fashion.
They dont have a central nervous system. They have something called a nerve net, which is basically just all their nerves are spread over their whole body. But they can still move in a co-ordinated directional manner. So they’ll have parts of their body which are detecting a stimulus, and they’ll move towards that or move away from it if it’s something they want to go to or something that’s annoying them.
Most sea stars have eyes on the tips of their arms. Learn more about these ‘eye spots’ in this blog by Ed Yong.
To extend learners, look inside a sea star to see the inner workings of an animal very different from us in this animation, Sea star body plan.
They have bony, calcified skin, which protects them from most predators, and many wear striking colors that camouflage them or scare off potential attackers. Purely marine animals, there are no freshwater sea stars, and only a few live in brackish water.
A starfish can eat anything he can fit in one of his two stomachs. He does this by pushing a stomach out of his body where it can safely digest large prey, like an oyster, and then pulls it back into his body after the food is mostly digested. The ability to eat prey of varying sizes is an advantageous adaptation for the starfish.
A starfishs arms are covered with hundreds of small suckerlike feet. These feet not only help him walk but give him strength to pry open shelled prey like clams and oysters. Since a starfish moves so slowly, he relies heavily on prey that doesnt move. The tube feet also help keep him anchored in place, such as on a rock, coral branch or the ocean floor, during a storm and against tide forces and ocean currents.
What passes for a starfishs circulatory system uses ocean water instead of blood. This is essentially a series of tubes that extend from the stomach to the arms to transport nutrients. A starfish doesnt have a heart, but water running through the arms and feet provides oxygen.
Unlike many sea creatures, starfish, also called sea stars, dont have gills or fins. In fact, they dont even have brains, hearts or blood. What they do have, however, is several specialized adaptations that allow them to survive in a constantly changing and dangerous environment filled with predators.
If a starfish loses an arm, an organ or even most of his body, he can regrow whatever part he needs as long as part of the central ring is intact. Thanks to this ability, if a predator attacks and manages to take a bite, a starfish wont bleed to death, get an infection or be permanently crippled. In fact, one starfish may become two if part of the central ring is attached to the part separated from the main body. Some starfish intentionally reproduce this way, by separating their own bodies in half, if the population is dwindling.
They move relatively slow so we wouldnt necessarily see them swimming or see them moving around. But certainly if you were to watch them for long enough you would see they are very mobile, and they move around using special structures called tube feet, which are like little tentacles with little suckers on the end of them, and an individual starfish will have 2 or 3 hundred of those. So it’s got these little tentacles, which are on its underside, which it uses to hold on to the rock wall or the wharf piling or whatever and move around in a co-ordinated fashion.
Sea stars have many weird and wonderful adaptations – including some unusual internal systems. Click on any of the labels in this interactive to view short video clips or s to learn more.
Sea stars are invertebrates so they don’t have a backbone, but they do have a skeleton beneath their skin. This endoskeleton is made up of a complex network of hard bony plates made of calcium carbonate and held together by strong flexible tissues.
Most sea stars have eyes on the tips of their arms. Learn more about these ‘eye spots’ in this blog by Ed Yong.
Sea stars have many weird and wonderful adaptations including both sexual and asexual reproduction. Click on any of the labels in this interactive to view short video clips or s to learn more.
To extend learners, look inside a sea star to see the inner workings of an animal very different from us in this animation, Sea star body plan.
Note: Red spots are also referred to as “eye spots”, they are located on the tips of their arms where their underside meets the top side.
When these animals reproduce, they release a free-swimming stage – it’s a microscopic larval stage – and that is in the water column, moving around for weeks or months, depending on what species you’re dealing with. And that’s a way that the animal can basically colonise different areas. It releases the larvae, they get washed away, then they settle out and turn into little starfish and grow up.
If a fish comes along and starts attacking a starfish – it might grab it by the arm – the starfish will happily let go of that arm through a process called autotomy, and it will just regrow that arm. So they have very good powers of regeneration. In fact, there’s research going on trying to understand how they can regenerate so well. Perhaps there could be some medical applications for us.
FAQ
What special adaptation do starfish have for moving in their habitat?
How do starfish adapt to the intertidal zone?
How do starfish protect their self?
- A Starfish is not a fish. …
- They have no brain or blood. …
- They weigh more than you think. …
- They live for a long time. …
- There are around 2,000 species of sea star. …
- Not all Starfish have five arms. …
- They cannot survive in fresh water. …
- They can regenerate.
