Starfish are marine invertebrates or "echinoderms" in the class Asteroidea. Scientists, therefore, prefer to call them sea stars. There are 1,800 to 2,000 species of sea stars that vary in size, color and other characteristics. We think of the sea star with five appendages, but some sea stars can have many more arms.
Sea stars range from almost 5 inches to more than 9 inches in size. Some can weigh as much as 11 pounds.
Sea stars can be sand- or neutral-colored, or brightly colored. Some are vivid fuchsias, reds and purples. A sea star's color depends on where it dwells or scavenges for food, since it camouflages the sea star from potential predators and intimidates potential attackers.
Sea stars with five arms are the most common type of sea star. However, other species of starfish have more -- some have 10, some can have 40. Regardless of how many arms a sea star may have, its eyes are located at the end of each arm. Sea stars can detect changes in lighting with their eyes.
Sea stars have thick, bony, calcified skin, which is covered in spines and protects them from most potential predators. They have stalks with tiny pincers that they use to keep debris from collecting on their skin and weighing them down.
Sea stars have tube feet located at the bottom of each arm. The sea star uses these tube feet to move around the ocean floor, drawing water in and releasing through the feet. The suctioning power of the tube feet allows sea stars to move around, cling to rocks, and catch and kill food.
The sea star's mouth is located at the center of the underside of the creature's central disc, the area from which its arms radiate. The starfish has a cardiac stomach and a pyloric stomach. Some species of sea stars have the ability to protrude their cardiac stomach from their mouths to grab and digest their prey.
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