True Facts About Starfish

Roughly 2,000 species of starfish inhabit the seas and oceans around the world. Some species dwell in the cold waters of the Antarctic regions, while others appear in tropical locations. Although they come in a variety of colors, shapes and sizes, all starfish share several common traits.

  1. Body Structure

    • Starfish aren't actually fish; fish are equipped with gills, fins and backbones. Starfish are echinoderms, invertebrates with radial symmetrical bodies. Rather than scales, most species of starfish have a tough, leathery skin, which offers protection from predators such as fish and birds. This skin is composed of calcium carbonate.

    Arms

    • Most species of starfish have five arms that extend from a central point; however, there are some exceptions. For example, the Coscinasterias calamaria can grow 11 arms, while Sunflower stars can grow up to 24 arms. The arms contain eyespots, which are light sensitive organs that aid in motion detection. Starfish can regenerate lost or injured arms over time. According to National Geographic, some species store vital organs in their arms, so separated limbs can regenerate into new starfish.

    Organs and Diet

    • Starfish don't have blood. Instead, filtered seawater plays the role of blood. Starfish also lack brain, but they have multiple stomachs. The cardiac stomach allows a starfish to consume prey, while a pyloric stomach completes the task of digestion. Starfish prey on clams, oysters, snails, barnacles and small fish. When consuming shelled creatures, starfish must first use their suction cups to create an opening before using their cardiac stomach.

    Predators

    • A variety of marine creatures, including sharks and manta rays, can break through the starfish's tough skin and prey on it. Birds can feast on starfish that dwell too close to the surface. In some cases, larger species of starfish may consume smaller species. If a starfish is fortunate enough to escape its many predators, it may live up to 35 years.