Facts on Starfish for Kids

Written by valerie a. modreski
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Facts on Starfish for Kids
There are over 2,000 species of sea stars inhabiting all the world's oceans. (Ablestock.com/AbleStock.com/Getty Images)

Science has recently undertaken the lengthy and difficult task of renaming all starfish to sea stars. The reason behind this endeavour is because this marine animal is not a fish, but a member of the echinoderm family which incorporates over 2,000 species, and is more closely related to sea urchins and sand dollars. The class name echinoderm comes from the Greek word meaning "spiny skin."

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What are Echinoderms?

Echinoderms have a great deal in common with each other as they all have skeletons made of bony plates, spines that protrude from their skin for protection and they each possess thousands of hollow, tubelike feet that propel them across the ocean floor.

All sea stars live in salt water. They can be found in every ocean of the world from the tropical shallows to the deepest of the icy polar seas. Some sea stars spend much of their time clinging to ocean reefs and rocks, while others prefer to transverse the sandy sea floor.

Physical Makeup

Sea stars are a complicated animal structure that has no brain. Instead, sea stars have special cells on their skin that gather information from their surroundings. These cells send signals through a network of nerves that initiate an action from the sea star.

The mouth on the sea star is on the underside centre of the animal's body and leads to an internal sack-like stomach. This stomach organ can actually be extended out through the mouth to devour prey.

Sea stars do not have eyes like people do. However, they have "eye spots." These are cells located on the tips of their arms that sense light and darkness only. Sea stars do not need to see, as they detect danger and food sources with the internal sensory cells of their nervous system.

Unusual Ability

Sea stars have a truly unique ability to grow entire new limbs when one is injured or broken off. Because they cannot move very fast, sea stars are always in danger from animals that prey on them and accidents that occur underwater.

Some species are so good at regeneration (replacing a body part with a new one) that they can actually grow whole new bodies from one broken off arm. This process may take up to a year, depending on the severity of the injury.

Are Sea Stars in Danger?

The biggest threat to sea stars is the same one that threatens most other animals in the sea: humans.

Sea stars need clear, clean water to live in. When people allow pollutants to run off into the oceans and seas, the sea stars get very sick and can even die. Also, many cultures eat sea stars. When too many are taken from any one area, and they do not have a chance to multiply, they can disappear entirely. This is called over harvesting.

Fortunately, most sea star species are thriving and as scientists continue to explore the deep oceans, they are discovering new species all the time.

Effects of Global Warming

Rebecca Gooding, a doctoral student in zoology (the study of animals) at the University of British Columbia, reports there are some concerns about the sea star's disappearing habitat and that "global warming is a factor." Coral Sea beds, the primary home for most sea stars, are not growing like they should because of the warmer waters.

Scientific studies have not yet narrowed down just what effect universal temperature change is having on sea stars. But right now the another obvious detriment from the warming water temperature is a decrease in food sources for the sea stars. Sea stars primarily eat clams, mollusks and snails, and these animals are being adversely effected by global warming because they do not multiply as fast.

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