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Animals, Plants and Habitat

Sea Star Identification on King County Beaches

Sunflower Star
Pycnopodia helianthoides

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This soft bodied sea star can be 80 cm in diameter -- the largest found in this region. The arms are relatively short (R/r = 2.5 to 3.5)*. It can move across the bottom at 160 cm/minute( more than 5 feet) which makes it the fastest as well. It feeds on whatever it can catch including hermit crabs, sea cucumbers, clams, urchins, sand dollars and bait.

* Two measurements need to be made in order to determine the relative length of the arms of a sea star. Simply stated, a sea star is made up of arms and a central area to which they are attached called the disk. Since a sea star has radial symmetry, their dimensions are referred to radii.

"R" is the length of the arm as measured from the center of the animal to the tip of the arm.

"r" is the radius of the disk and is measured from the center to a notch between the arms.

R divided by r (R/r) is the relative length of the arm. For instance: Distance from center of the disk to the tip of the are is 10" and the distance from the center to the notch between the arms is 2 1/2", then: R/r = 10/2.5 = 4