Mermaid's FanUdotea spp.
The Mermaid's Fan is a Green Algae. The several species here represent a few of the types found in sandy sea floor environments, the silty bottoms of the mangroves and in areas of rock and rubble. It seems there is a species that tolerates full daylight and those that do well in shady areas. There is the flat paddle-like fan, the accordian folded and the double layered grown patterns. These are not plants in the strict sense of the word.