Colonies are free-living and irregular in shape, with an axial furrow that may become indistinct. The wall is thin. Septo-costae radiate in a fan from a central corallite or are perpendicular to the colony margin, in which case they form distinctive lines of demarcation (see black-and-white photograph of skeleton, below). Primary septa are petaloid and form neat rows embedded in fused septa of lower orders. Tentacles are extended during the day giving colonies a hairy appearance.
Protected reef slopes and lagoons.
Sometimes common due to mass reproduction by autotomy.