* An Orange  Cup Sponge (Mycale sp.)  with Black Brittlestar (Ophiothrix sp.) Note the transparent rim on the sponge mouth, It is characteristic of the Mycale species. 

We have noticed that when either the Orange or Red Cup Sponge is associated with Brittlestars (Ophiothrix sp.), the Brittlestar is always black  (1), (2) .  Since Orange and Red Cup Sponges appear glossy black at depths that the Mycale species. are normally encountered, we speculate that to an underwater predator, the black Ophiothrix would be almost invisible.  Only the dive light separates the sponge and the Brittlestars.

Jackson Bay, Little Cayman Island  -  Depth 125 feet or 38 meters