Arabian Crust-sponge

Found on dead or living corals, in well lit areas of coral and rocky reefs. Varies in colour but usually a dark blue/black

Sponges come in a range of sizes from minuscule encrusting species under rocks to massive sponges which can be up to one and half metres high.
They are able to filter many litres of sea water every few seconds.
Sponges can exude highly toxic chemicals and so have very few predators apart from nudibranchs, sea stars, sea urchins and umbrella shell.
Their colour can vary if growing in the light or when growing in the shade.