Not the garden variety. This is commonly called a ‘Warty Slug’ which belongs loosely to the family of nudibranchs. Warty Slugs carry toxins in their skin to deter fishes from feasting on them, and like so many animals in the world, they also advertise their toxicity with bright contrasting colours. Here we see the ‘classic’ combination of black, white and yellow.
This (heavily cropped) photo is really stretching the macro capabilities of my S95, but I wanted to show the bryozoans that the slug was eating. Bryozoans are fairly basic animal life forms, they look like tiny fern trees, and encrust much of the reef wall. They are easier to see on metal objects such as those found on shipwrecks.