Older juvenile (another of the many seen this dive, and I imaged at least 7-8 individuals adequately for facial recognition).
Mimicking Galeolaria worm casings, apparently, having been disturbed when I turned an old bit of wooden pile remnant lying on the bottom.
Older juvenile or younger adult, hard to decide. Close to the beach,and a snorkeler will usually see a few of these (mainly juvenile and rarely full adult size) on any warm season snorkel here (at the exact location I've described above).