Red pencil urchins

Red pencil urchins add striking color to the reef
Red pencil urchins add striking color to the reef, seen here among cauliflower coral and, what I think are, black banded urchins.

To identify this, I used John P. Hoover’s book Hawai‘i’s Sea Creatures: A Guide to Hawai‘i’s Marine Invertebrates. His website is hawaiisfishes.com.