Jellyfish and starfish are beautiful animals that share a few similarities even though they look nothing alike. Both lack brains or skeletons, and neither are fish at all. They are marine animals, meaning they live in the salt water of the ocean. Aside from these similarities, jellyfish and starfish are very different.
Starfish, also known as sea stars, are classified as echinoderms because their bodies are made of calcium carbonate components called ossicles. Starfish, which can regenerate limbs, can have anywhere between five and 50 arms depending on the species. Starfish also have a small eye spot in the middle of their bodies that allow them to differentiate between light and dark. Jellyfish are classified as Cnidarians because they have tentacles that sting. They are basic organisms with a thin layer of skin and a primitive digestive system. Most species are extremely small, but some have tentacles up to 100 feet. While Starfish are solid creatures, the jellyfish is very slight. It is 95 percent water.
Starfish have hundreds of tube feet on their underside that work like legs to push the starfish forward. The tube legs can act like suction cups the Starfish will use to stick to or climb walls or rocks. Starfish can move up to 20 feet per hour. Jellyfish are free-swimming creatures that ride the ocean currents to get from one place to another. They have limited control of where they're going when it comes to horizontal movement, but have muscles to move up or down.
Diet and Hunting
Starfish use their legs to pry open the shells of prey like oysters and clams. A sack-like stomach comes out of its mouth, oozes into the shell, then retreats back into the starfish's body. Most of a jellyfish's diet is composed of zooplankton, comb jellies, and occasionally other jellyfish. The jellyfish will wait for prey to float into its tentacles. It will launch thousands of tiny filaments into the prey, and the barb-like ends of the filaments will inject the prey with venom. Tiny arms around the mouth of the jellyfish bring the immobilized food in for consumption.
Starfish and jellyfish can be found in every ocean in the world. Starfish usually stay on the ocean floor or cling to rocks near the shore, but occasionally float on the top of the water. Depending on the species, jellyfish will be found in shallow waters near the coastline or middle waters deep out in the open sea.
About the Author
Nikole Yearout started writing in 2003. She writes for various websites, covering everything from marine biology to online programming and book publishing. Yearout is pursuing a Bachelor of Arts in creative writing from Washington State University.