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This animal is usually between 2 and three inches in diameter making it one of the smallest sea stars found in the central and south Puget Sound. The relative length of the arms is somewhat short (R/r = 2.8 to 5.0)*. While it resembles a juvenile Mottled or Purple sea star, the bands on the arms help identify the Six arm Sea star.

* 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