Sea slug or nudibranch
Slugs are snails that have got rid of their shells. Shells are good for protection, but it stops you from going to many places. A shell is a drag. Sea slugs are also called nudibranchs. There are two main reasons for being a colourful show off in the animal kingdom. Some animals are colourful so they find the right mate or males compete to get the best mate.
Other animals like sea slugs are colourful as a warning that they are dangerous or taste revolting and you had better stay away. Some nudibranchs make a yucky tasting slime. Others eat poisonous stinging anemones or sea jellies and are able to take the stings and plant them in their body for protection. This sea slug eats sponges and can extract the poisonous chemicals to protect itself.
That is not a punk hairdo on the nudibranch. They are naked gills for getting oxygen from the water. In this photo, there are two nudibranchs. Find the two masses of naked gills. Their heads are hidden together. Are they eating the same food or are they saying hello?
Their eyes are almost useless, so their tentacles do all the work sensing touch, smell and taste. They can crawl slowly on their muscular foot, swim gracefully or because there is no shell squeeze themselves between rocks.
You can check out Australian nudibranchs on this website www.nudibranch.com.au