Rocky coastal critter ID

[Carey]

It was one of the critters I had to know for a UH-Hilo Quest Marine Science class ( the clues of round & skirt of elongated plates & the fact that it was not a chiton, which has overlapping plates like the Hawksbill sea turtle) The fact that I had to look up the name tells you how well my memorization works! Only remebered there was an urchin with inter-tidal flatten spines & it had lobocentrus in the name, but had my class materials to fall back on!
Aloha, Carey