Welcome to brain Stuff production of I Heart Radio, Hey brain Stuff lorn Volga Baum Here. While starfish live underwater, they're not actually fish at all. In fact, marine scientists have replaced the beloved starfish is common name with the name sea star because the starfish isn't a fish? So what exactly are they? For the article this episode is based on How'stuff works, spoken by email with Kim Stone,
the Georgia Aquarium's curator of Fish and Invertebrates. As she said, they're a type of invertebrate, meaning they don't have a backbone. Their body consists of a central disk with arms that radiate out and on the underside there are hundreds to thousands of small suction cups called tube feet that helped the c star move around, stick to different surfaces, and eat. There are some other big differences that set starfish apart from fish. These cool creatures don't of gills, scales, or fins.
They live only in salt water, and they use sea water instead of blood to pump nutrients through their bodies by means of a water vascular system, unlike fish that have gills and mammals that have lungs. See stars breathe by absorbing oxygen from the water through different parts of their body, such as their skin and tube feet. Stone explained sea stars belonged to a group of marine invertebrates called kinoderms, which first appeared more than five hundred million
years ago. The ancestors of modern day sea stars appeared more than four hundred and fifty billion years ago during the or Division period. Chinoderms include five classes of marine life see stars, brittle and basket stars, sea urchins and sand dollars, sea cucumbers and sea lilies, and feather stars. There are around two thousand different species of sea stars. A Stone said they can be found in a variety of habitats, from shallow sandy bottoms, cold rocky environments to
the bottom of the sea floor. The different species have many different features, but all have their mouth on their underside. Upon capturing food, often a bivalve such as a clamor muscle with its tube feet, the sea star wraps its arms around the animal's shell and pulls it open just slightly. Then the sea star pushes its stomach through its own mouth and into the praise shell. It then digests the animal and slides its stomach back into its own body.
This unique feeding mechanism allows the sea star to eat larger prey than it would otherwise be able to fit into its tiny mouth. But starfish eat a wide variety of planted animal life, and they're chosen menu can depend on the species, the Stone said. Many species are scavengers and carnivores that eat gastropods, bivalves, barnacles, marine worms, and
other invertebrates. In some species are suspension feeders that capture plankton and organic material from the water or and some species of c star may have as many as ten, twenty, or even forty arms. Although starfish have five point radial symmetry, that doesn't mean that all of them have five arms. Furthermore, if one of these arms is lost, a sea star
has the amazing ability to regenerate it. The ability to regenerate lost arms is especially useful if a c star is injured by a predator, it can drop an arm, escape and grow a new one later. This won't happen too quickly, though, it takes about a year for an arm to grow back, as some require the central body to be intact in order to regenerate. But a few species can grow an entirely new sea star from just a portion of a severed limb, depending on which organs
that limb houses. Sea stars also have an eye spot at the end of each arm. That means of five armed sea star has five eyes, while the forty armed sun star has forty eyes. Each c star eye is very simple. It looks like a red spot. It doesn't seem much detail, but consents light and dark, and that's just enough for the environments in which these animals live. And speaking of the average lifespan of a starfish is
an impressive thirty five years. A large starfish species tend to live longer than their smaller counterparts, but however long they live, see stars don't swim. They instead use those tube feet, hundreds of small suction cups on the underside of their bodies to move from one area to another. The tube feet also helps sea stars hold their prey. Some starfish do have spiky protrusions, but generally they're not dangerous to us, though we humans are dangerous to them
because they're literally shaped like stars. Humans have the tendency to keep starfish as souvenirs, or even hold them out of the water for photos. But forcing starfish out of the water or throwing them back in can do serious damage, and starfish have intricate, fragile arms and tiny body structures to spite their regeneration capabilities. Even the slightest poke can
hurt them. Aside from that, human hands are naturally dangerous to all seek creatures due to the billions of bacteria that exist on our skin, and contact can lead to a possible slow death, so if you have the chance to see one, appreciate it from a respectful distance. Today's episode is based on the article some starfish have up to forty arms, plus ten other starfish facts on how stuff works dot Com, written by Wendy Bowman. Brain Stuff is production by Heart Radio in partnership with how stuff
works dot Com, and it's produced by Tyler Klein. Four more podcasts my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.