Leather Mushroom Corals
This specimen is on a rock: the red patches are encrusting sponge. The tentacles of a curlicue anemone are on the right, and a yellow watchman goby can be seen on the left. There also is a snail on the rock in the right background.
A close-up of the mushrooms reveals many tiny hairs (probably to capture food) and some white "spikes" (center of the picture). At first I thought the spikes were parasites (baby nudibranchs), but it turns out they are calcium spikes which are used to stiffen the coral structure.