Changes

They are related to [[sea slugs]] and [[sea cucumbers]], <ref> http://www.madsci.org/posts/archives/may98/892688355.Zo.r.html </ref> but unlike those creatures asteroids aren’t edible by humans. In fact, they aren’t edible to many creatures – their spiny skin and awkward shape makes them distasteful to most. They also have tiny structures like pincers, called ''pedicellariae'', that are probably used for defence defense as well as capturing small particles of food. They are found all over the world, and at all depths of the sea, though they tend to favor rocky shallows. <ref>http://library.thinkquest.org/TQ0311542/starfish.htm#Info</ref>

Starfish eat almost anything that cannot easily escape, but mainly [[bivalves]]. They eat these by using their tube feet as suction cups to prise a small gap in the bivalve’s shell, and then everting reverting their own stomach through their mouth opening and extending it into the shell, using their digestive juices to liquefy the creature inside and then sucking it in. Starfish help the intertidal [[ecosystem]] stay in balance by eating mussels, which would otherwise push other organisms out. <ref> http://oceanlink.island.net/ask/echino.html </ref> The crown-of-thorns starfish (Acanthaster planci), which feeds on [[coral]], is decimating [[coral reefs]] off the [[Philippines]] and [[Australia]].

A starfish doesn’t have a front end; any side of a starfish is as likely to be the front as any other side. They also don’t have [[ears]] or image-forming [[eyes]], though they do have [[eyespots]] on the end of each arm containing a red pigment that changes chemically in the presence of light and are thought to influence the starfish's behaviourbehavior. <ref>http://findarticles.com/p/articles/mi_m1169/is_2002_Feb-March/ai_89436290</ref>

Starfish don’t have a central [[brain]]. A radial [[nerve]] runs down each ray, and connects with the other radial nerves through ganglia that form a ring in the centre center of the starfish. Because the starfish’s mouth is in the centre center of the underneath of its body, this is called the circumoral nerve ring. It does not control the rays though, merely facilitates communication between them. Any radial nerve can take control of the body of the starfish by signalling signaling the others to co-ordinate movement in the direction of the ray it runs down. However, as well as locating food and mates, starfish can learn to associate different textures of seabed or levels of light with food, and as well as distinguishing between odours odors can learn to ignore those not associated with food even if they smell like food.<ref> http://www.vsf.cape.com/~jdale/science/science.htm </ref>

Like a lot of other marine creatures, a starfish’s primary sense is [[chemoreception]]. Leading rays tend to raise their tips and wave their tube feet around. They use their tube feet to sense the concentration of chemicals, comparing the intensity of the information between rays and moving accordingly to reach the source of the odourodor, so it would be true to say that they have multiple noses in their feet. Because starfish are too primitive to have consciousness, their sleeping and waking cycles can only be determined by different firing rates of nerves in response to changes in light intensity. They feed in response to odours from [[prey]]. <ref> http://www.vsf.cape.com/~jdale/science/science.htm </ref>

Starfish eat almost anything that cannot easily escape, but mainly [[bivalves]]. They eat these by using their tube feet as suction cups to prise a small gap in the bivalve’s shell, and then everting reverting their own stomach through their mouth opening and extending it into the shell, using their digestive juices to liquefy the creature inside and then wafting the liquefied juices into its mouth with its tube feet. This enables a starfish to hunt much larger prey than it could actually fit into its mouth. Starfish help the intertidal [[ecosystem]] stay in balance by eating mussels, which would otherwise push other organisms out. <ref> http://oceanlink.island.net/ask/echino.html </ref> The crown-of-thorns starfish (Acanthaster planci), which feeds on [[coral]], is decimating [[coral reefs]] off the [[Philippines]] and [[Australia]].