Just what is a sea star?
Sea stars live in the ocean, but they are not fish. Fish are vertebrates (backbones) that have gills and fins. Most have scales. Sea stars do not have any of these characteristics. Since they are not true fish, scientist call them sea stars instead of their common nickname: starfish.
Sea stars are spiny skinned animals that are related to sea urchins, sea cucumbers, and sand dollars. These animals have five point radial symmetry and are covered with bumpy, spiny skin.
How does a sea star move?
The underside of each arm on the sea star's body is covered with two rows of tiny tube feet. At the end of each foot is a little suction cup. The suction cups allow the animal to move, grab onto rocks, and hold it's prey.
How do sea stars hunt for prey?
Sea stars like to eat bivalves for dinner, and they are mighty predators. Two shelled animals like scallops, clams, mussels, and oysters are on their menu.
When the sea star finds a tasty prey, it wraps it's arms around the bivalve's body. Using the suction from it's tube feet, the animal pulls the bivalve's shells apart. After the shells are open, the sea star pushes it's stomach outside it's body and into the bivalve. Using digestive enzymes, the animal consumes the bivalve's soft body tissue.
The more the sea star eats, the larger it's body grows. Age has nothing to do with the size of this animal.
So the next time you find a large sea star, just remember...you're looking at a very skilled hunter. To a bivalve, sea stars are the 'sharks' of the ocean.
1. "Are starfish really fish?". National Oceanic and Atmospheric Association (NOAA): National Ocean Service. Web. 03 Oct. 2018. <https://oceanservice.noaa.gov/facts/starfish.htmlhttps://oceanservice.noaa.gov/facts/starfish.html>.
2. "Sea Star". Adapted from The Uncommon Guide to Common Life on Narragansett Bay: Save the Bay. Web. 06 Oct. 2018. <https://www.edc.uri.edu/restoration/html/gallery/invert/sea.htm>.