This Strongylocentrotus droebachiensis (Green Sea Urchin) was an inch and a half across. It was attached to a rock during the minus tide.
This Strongylocentrotus purpuratus (Purple Sea Urchin) is underwater, so its tube feet are visible. I saw dozens of Purple Sea Urchins, some living in holes they had drilled into rocks.
Here's the only Strongylocentrotus droebachiensis (Green Sea Urchin) I saw at Tonge Point, where there were dozens of Purple Sea Urchins. This one was particularly beautiful, with its 5 stripes quite visible.