Zoopilus echinatus looks very similar to Halomitra pileus but is apparently distinguished by the inconspicuous calices, which are muchy more prominent on Halomitra. This species can be found at least on lagoon reefs and pinnacles, and possibly on some seaward reefs.
The corals can sometimes become flipped upside down, likely by the actions of fish seeking hidden prey.
The two photos below show the same individual taken nearly 4 years apart.
Created 8 June 2023