SEA STARFeatured in the "Creatures of the Deep" episode of Life.
 More LifeSea stars are one of the most recognizable marine creatures, with more than 2,000 species strewn around the world's oceans. Also known as starfish, they appear in varying colors, including shades of brown, red and orange that act as camouflage. Their coloring and their tough, calcified exterior can deter potential predators.
Like the sea cucumbers, urchins and sand dollars they're related to, sea stars are not actually fish, but rather echinoderms. These carnivorous invertebrates seemingly get along well without a brain, living as long as 35 years in the wild. From arm to arm, a typical starfish will stretch about a foot across. Most have five arms, although some may boast up to 40. At the end of those signature appendages is, remarkably, a sort of eye, equipped with light sensors.
SERIOUS SUCTION
Without suction, all those arms wouldn't be nearly as useful. The suction stems from a spot called a madreporite, located near the center of the sea star's body. The organ acts as a powerful pump, pulling seawater into the star and along the various canals that run through the animal's body. The pumping action creates suction in the star's hundreds of tube feet, which allows it to move and to grasp onto surfaces, including future meals. Sea stars also can use their tube feet to wrench open bivalves, such as mollusks, clams and oysters. The suction system eliminates the need for blood; filtered seawater serves in its place.
THAT'S ONE AMAZING STOMACH
As seen in Life, sea stars eat by pushing their stomachs through their mouths, which are located in the center of the animal. The subsequent effect looks something like a pulsing heart, as the star emits corrosive digestive fluids that help to dissolve the prey's flesh. The stomach then consumes the liquefied food and draws it back into the star's body. Sea stars eat voraciously. One star might consume a few dozen small clams in a week. Stars grow according to how much they eat — not according to their age — so a large sea star often indicates a well-fed one.
Sea stars are plentiful for at least two reasons. First, they reproduce like mad. One female star may have as many as 2.5 million eggs in her arms during a single mating season. Second, they're adept at survival, thanks to their famous ability to regenerate arms. That ability comes in handy when fending off their natural predators, which include crabs, fish and birds.
Written by Jacob Silverman, HowStuffWorks
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