This beautiful short clip shows a five-legged starfish (or sea star) walking along the wall of its tank. The video has been edited and sped up, as starfish actually move very slowly. The stunning, bright coloration of the starfish causes one to wonder what kind it might be. After some deep-diving research, we discovered it’s a chocolate chip sea star (Protoreaster nodosus). This beautiful starfish has lots of feet that help it in many ways. Let’s learn more about this species and other sea stars!
How Many Feet Do Starfish Have?
Generally, starfish have hundreds or even thousands of little feet that allow them to move along the ocean floor or their tanks. These feet are hollow and filled with water. For this reason, they are called tube feet, but the actual name for them is podia (individually, podium). Each podium is connected to a sack called an ampulla. When the starfish wants to move, it squeezes the ampulla to move the podium. This type of movement is called hydraulic movement because it uses hydraulic pressure (pressure from the movement of water).
Sea stars don’t have blood, their circulatory system is filled with seawater, instead! Sea stars also use these tube feet to bring food to their mouths and to cling to surfaces. Some starfish have very strong podia, like the nail starfish (Mithrodia clavigera).
Can Sea Stars Have More Than Five Legs?
Yes! Technically called arms, most sea stars have five. However, they can certainly have more. Sunflower starfish (Pycnopodia helianthoides) start life with only five arms, but grow 16-24 arms as adults. The Antarctic sun starfish or wolf trap starfish (Labidiaster annulatus) can have as many as 50 arms.
Each of the starfish’s arms contains its feet and an eyespot at the end. These eyespots don’t see colors and details like our eyes do. They can only tell the difference between light and dark, which helps them find food. The sea star grabs food with their arms which bring it to their mouth. While their feet hold on tight, the starfish wraps its arms around the food or prey. Then it pushes its stomach out through its mouth to wrap around the food and digest it. Isn’t that neat?
What Is a Chocolate Chip Sea Star?
This type of starfish is found in the Indo-Pacific region, which includes the Indian Ocean, the western and central Pacific Ocean, and all the water between the two. Also called the horned sea star or knobby sea star, it lives in shallow water and eats corals, sponges, and sea snails. Usually, these starfish come in white with dark knobs and pink feet, though some can have bright red shells. They can also be brown, blue, or yellow. Due to the unique beauty of its shell, this species suffers from the shell trade. The shell trade and the aquarium market remove many of these creatures from the wild.
In the wild and in captivity, the chocolate chip starfish’s average lifespan is about 20 years. They make great additions to tanks with fish, but should not be kept in the same habitat with corals and sponges, since they eat those. If you have a pet starfish, you should try very hard not to handle it. They do not do well with sudden changes. These sensitive and fragile creatures need specialized care to live well.
What Are Some Interesting Facts About Starfish?
We already learned that starfish have very useful feet and that they eat their food by pushing their stomach out through their mouth. Some starfish can be dangerous, like the crown-of-thorns starfish (Acanthaster planci) which has sharp spikes on its shell. Sea stars are very interesting creatures!
Here are some more fun facts about starfish:
- Starfish do not have brains. We learned earlier that they do not have blood, but they do not have brains either. That’s because they have adapted to live without these things. Their nervous system is powered by water that carries nutrients throughout their body. Without water, a starfish cannot live.
- Some starfish leave the water for short periods. Although sea stars require water to live, some of them can leave the water for up to 26 hours! However, starfish cannot breathe when they are out of the water. If you find a starfish on the shore, gently move it back to the water. Even if it has already died, the nutrients from its body need to go back into the water to help keep the balance of the ecosystem. Take care not to touch the sea star too much. The natural oils on our skin along with products such as perfume, lotion, or sunscreen can damage the delicate creature.
- Starfish cannot live in freshwater. Sea stars are called that for a reason. They must live in the sea (ocean) because they need salt water to carry oxygen and nutrients through their bodies. However, they cannot live in water that has too much salt, either, like lagoons.
- Starfish feet don’t use suction. It is a common misconception that starfish feet are like suction cups. A study published in 2012 shows that sea star feet actually use a glue-like substance to hold onto things rather than using suction. In contrast, octopuses and squids both have suction cups on their arms.
Try to Count How Many Feet This Starfish Has as It Walks Along!
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