We are guessing this is a species of Halomitra. It forms flattened, thin, very lightweight plates that easily break apart. Many of the plates probably exceed 40cm in diameter. The few times we have found this species, it has formed clusters of plates, many naturally broken, spread over several meters of deep lagoon bottom. We have seen it at depths of about 35-40m around the bases of some lagoon pinnacles, such as the one at T-Buoy.
Created 10 April 2020