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Natural Perspective

The Animal Kingdom: Starfish (Asteroidea)

(Last modified: 23 July 1997)
[icon: ochre-rayed star][icon: bat star][icon: six-rayed star]

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.

[photo: pink star] 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.

[photo: leather star] 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.

[photo: knobby star] 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.

[photo: sunflower star] [photo: bat star]

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.

Phylum: Echinodermata (Spiny-skinned Tide Pool Creatures)
Class: Asteroidea (Starfish)
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