Starfish are echinoderms (spiny skinned sea urchins). They’re also known as sea stars, however despite their name, they’re not actually fish. Starfish are unable to swim and do not breathe through their gills. See the fact sheet below for more information on these fascinating sea urchins:
- There are more than 2,000 different species of starfish. Echinoderms all exhibit five-point radial symmetry, which implies their body plans are organized around a central disk in five portions.
- Starfish can be found in both the deep blue ocean and shallow water. They can be found in all of the world’s oceans. They have never been discovered in fresh water.
- The majority of starfish have a prickly shell that protects them. The skin of a sea star can be leathery or slightly spiky, depending on the species. Plates of calcium carbonate with microscopic spines on their surface make up the tough covering on their upper side.
- The spines of a sea star protect it from predators such as fish, sea otters, and birds. Starfish are available in a wide range of colors, as well as patterns.
- While the five-armed sea stars are the most well-known, sea stars do not all have five arms. Some people have a lot more. Consider the sun star, which can have up to 40 arms.
- The armspread of the Coscinasterias Calamaria, popularly known as the eleven-armed sea star, can reach 30 cm. It does have eleven arms, as the name says, but the number can increase up to 14 at times.
- Sea stars have the incredible ability to repair damaged limbs. If the sea star is endangered by a predator, this will come in handy. To escape away, the starfish can drop an arm. Because most of a sea star’s important organs are housed in its arms, some can regenerate a new sea star from just one arm and a bit of the star’s core disc. This takes almost a year to complete.
- On the underside of their bodies, starfish contain hundreds of small projections known as tube feet. The starfish’s tube feet enable them to glide along the ocean floor and open on the scallops and clams they hunt for sustenance.
- There are two stomachs on the starfish. The starfish’s food is eaten by the cardiac stomach, which is located outside the starfish’s body. The food in the cardiac stomach is transferred to the pyloric stomach when it returns to the body. The cardiac stomach is stretched into the shell after the tube feet open the prey’s shell to pull the food inside. The tube feet are vital in assisting the starfish in obtaining nourishment. The oysters or clams are opened with the tube feet. The stomach is then expanded into the shell, allowing the food to be pulled within. They eat mussels, clams, tiny fish, snails, and barnacles, among other things.
- Sea stars have a water vascular system instead of blood, in which the sea star extends its tube feet by pumping sea water through its sieve plate, or madreporite. The tube feet are retracted by muscles within the tube.
- At the end of each arm, the starfish has minuscule eyes that allow it to see movement and distinguish between light and dark. They don’t see much detail, though.
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