Results: Sea Stars
Starfish (or sea stars) are beautiful marine animals found in a variety of colors, shapes, and sizes. All starfish resemble stars, and though the most common have only five arms, some of these animals can grow up to 40 arms. The amazing sea creatures—part of a group of animals known as echinoderms—travel using their tube feet. thoughtco.com is the source for this two-part series.
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Which of these sea star facts are you aware of?
Although sea stars live underwater and are commonly called "starfish," they are not true fish. They do not have gills, scales, or fins like fish do.
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Sea stars also move quite differently from fish. While fish propel themselves with their tails, sea stars have tiny tube feet to help them move along.
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Because they are not classified as fish, scientists prefer to call starfish "sea stars."
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Which of these sea star facts are you in the know about?
Sea stars belong to the phylum Echinodermata. That means they are related to sand dollars, sea urchins, sea cucumbers, and sea lilies. Overall, this phylum contains approximately 7,000 species.
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Many echinoderms exhibit radial symmetry, meaning their body parts are arranged around a central axis.
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Many sea stars have five-point radial symmetry because their body has five sections. This means that they do not have an obvious left and right half, only a top side and a bottom side.
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There are thousands of sea star species. Which of these facts are you familiar with?
There are about 2,000 species of sea stars.
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Some live in the intertidal zone, while others live in the deep water of the ocean.
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While many species live in tropical areas, sea stars can also be found in cold areas—even the polar regions.
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While many people are most familiar with the five-armed species of sea stars, not all sea stars have just five arms. Some species have many more, such as the sun star, which can have up to 40 arms. Before today's survey, had you heard about sun stars with up to 40 arms?
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Which of these sea star facts are you well informed about?
Amazingly, sea stars can regenerate lost arms, which is useful if a sea star is injured by a predator. It can lose an arm, escape, and grow a new arm later.
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Sea stars house most of their vital organs in their arms. This means that some species can even regenerate an entirely new sea star from just one arm and a portion of the star's central disc.
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This won't happen too quickly, though; it takes about a year for an arm to grow back.
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Which of these sea star facts are you up to date with?
Sea stars are protected by their natural armor.
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Depending on the species, a sea star's skin may feel leathery or slightly prickly. Sea stars have a tough covering on their upper side, which is made up of plates of calcium carbonate with tiny spines on their surface.
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A sea star's spines are used for protection from predators, which include birds, fish, and sea otters. One very spiny sea star is the aptly named crown-of-thorns starfish.
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