White encrusting zoanthid
Palythoa caribaeorum
Duchassaing
Description:
The colonies form thick, incrusting mats on dead corals and other hard substrates. The skeleton is hard, somewhat cork-like in consistency. The outer surface is covered with large, round calyces surrounded by a low, rounded ridge or lips. The fleshy polyps have short, stout, rounded, tentacles in two rings. Oral discs pushed against one another when fully expanded (P. caribaeorum-close up). Oral discs up to 1.3 cm in diameter.
Color:
Brownish-white.
Habitat:
Inhabit shallow reefs in areas with some water movement, down to 12 m. If the tentacles are retracted the colony forms a dome-like lump.
Distribution:
Occasional Florida, Bahamas and Caribbean.
Remarks:
The related Knobby zoanthidean (Palythoa mammillosa ) forms small mats, rarely exceeding 10 cm across, and the oral discs are separated by polygonal dividing lines and do not touch when fully expanded.