This one could be Comanthus parvicirrus, a species reported by Zmarzly (1985) from Kwajalein. We have seen it on lagoon pinnacles and seaward reefs, where it usually hides under rocks or in crevices during the day, sometimes with its arms showing.
Although those we see are usually all black, from other areas they have been reported to be variable in color. It is possible the one below represents the same species.
Created 24 March 2019