Brittle star

The brittle stars are echinoderms, (which means spiny skin) and are usually found in the coral reefs and shallow waters almost everywhere on earth. Brittle stars have over 2,000 different species. Amphipholis squamata are the most common brittle star. They are closely related to the sea star and the basket star.

Like most star fish, the brittle star has amazing regeneration capabilities. If a Brittle star gets one of its arms bitten off they can regenerate a new arm. Some star fish can survive with only one arm left intact, and regenerate the rest of the body.

Anatomy
They usually cling to coral with their arms which have little hook like spines. In all brittle stars there is a central disk that can grow up to 20 mm in diameter. They have a hard exoskeleton which means that they don't have a skeleton on the inside but a hard shell on the outside. They do not have a brain; instead they have a simple ring of nerve cells that transfers information around the body. Brittle stars have only one set of internal organs. Unlike star fish the Brittle star rows their arms though the water, kind of like a snake, to get from place to place. Star fish have to use their tubed feet to get around. Instead of having eyes they use the hairs on their arms to feel along, and smell. Their arms are made of little rings held together with muscle-like tissue, all attached to the center disk. Their five long legs (or arms)are also good for helping them move and capture food. Unlike star fish though, the Brittle star’s legs don’t touch at the center. On each segment of the legs are seven glassy spines that collect plankton. All of them can be different colors, the most common of the Brittle stars are: red, yellow, orange, violate, gray, and brown.

Reproduction
Most Brittle stars are separate sexes. They discharge their eggs into the water though their “Bursal slits”. The diameter of the eggs are around 1-0.18 mm. Like many other animals, Brittle Stars go though metamorphosis. That means that they go through stages before they reach maturity. These eggs start out as a sort of plankton only having legs. They then go into a larva stage. The body of the young eggs starts to flatten and close up, and then slowly forms into a Brittle star.



Ecology


All types of star fish are carnivores and love to use their five teeth to chew up the dead things on the bottom of the ocean floor. They usually eat on detritus or on worms, crustaceans and bivalves. They are known for being one of the best scavengers of the sea; along with sea urchins. They use their long spines to catch and bring in food to the mouth in the center of their body. Some Brittle Stars have little suckers on the bottom of their arms; but they don't use them to pull themselves along, unlike the normal sea star. But instead they use mucus on them so they can stick it to what they want to eat and pull it in. They're brittle and break away easily if they come under attack. In other words they can allow their arms to fall off to distract their enemy and can then get away. That's why they are called Brittle Stars. You usually find the this kind of star fish in massive groups. They are then able to gang up on something and eat their pray live instead of dead. 

Related References

 * Brittle star wikipedia
 * Brittle star Enchantedlearning


 * brittle star answers.com


 * Marine Environment - Brittle Stars