For now, I'll share one of my favorite pictures from a tidepooling excursion today:
This is a small juvenile Giant Sea Star (Pisaster giganteus). It was only ~6 cm (2.3 inches) across. Can you see the short, purple-colored spines? [Click on the photo for a slightly larger version.] That's one way to differentiate a Giant Sea Star from an Ochre Sea Star.
For some close-up images of Giant Sea Star spines, review the post from 26 April 2013.