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The Animal Kingdom: Starfish (Asteroidea)(Last modified: 23 July 1997)
If you've ever had the pleasure to go tide pooling then you already know that Starfish are the most popular creatures there -- especially among the younger crowd.
Tide pool excursions are a wonderful experience: the sound of surf accompanied by the refreshing sea breeze are reason enough to go. But the diversity of creatures living between sea and sand are the real treat on these trips.
At the shoreline, a certain camaraderie pervades the atmosphere.
Strangers approach one another to share information about interesting
finds; families with younger children ask: "Have you seen any
starfish?" [like the Pink Star (Pisaster
brevenspinus) to your right]; students follow teachers who are
thoroughly enchanted by the tide pool ecosystem; and perfect strangers
who may never meet again form close friendships while wandering in
search of another unusual living creature in the small pools formed by
the receding tide.
Starfish may well be the most unusual well-known creature. They have no front or back: they can move in any direction without turning. Rather than using muscles to move their hundreds of tiny legs, starfish use a complex hydraulic system to move around or cling to rocks. The intake valve for this system is generally located on the top of the Starfish, just off center, as can be seen clearly on the Leather Star (Dermasterias imbricata) to the left.
If you've ever tried to pry a Starfish off a rock, you know how effective its hydraulic system really is.
Of course, starfish don't have to make themselves symmetrical. They can rearrange their arms any way they please in order to wedge themselves into a small nook in the rocks -- as you can see in this almost human-looking Knobby Star (Pisaster giganteus) to the right.
Starfish are usually fairly sluggish, have five or six arms and get
pretty stiff when you try to pick them up. The Sunflower Star
(Pycnopodia helianthoides, below) breaks all of these
stereotypes. It typically has around 20 arms, moves --
practically flows -- quite gracefully across the surface, and is soft
(mushy?) to the touch.
Just for the record, the Starfish at the top of the page are:
Ochre Star (Pisaster ochraceous), Bat Star
(Patiria miniata), and Six-rayed Star (Leptasterias
hexactis) respectively, from left to right. The mottled Starfish
above right is also a Bat Star.
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