The common name for this little creature is Striped Pajama Nudibranch. Its scientific name is Chromodoris quadricolor. These nudies are small -- less than two inches (5 cm) in length -- but their bright colors make them easy to spot.
This species is very common in the Red Sea. In fact it is probably safe to say that this is the nudibranch seen most frequently by Red Sea divers. C. quadricolor also is found elsewhere in the Indo-Pacific region. They are sponge eaters.
Those two orange structures sticking up from the forward end of the creature are its rhinophores - sensory organs that help it navigate and find food. The rhinophores sense chemical molecules in the water similarly to how we sense smells in the air.
The bunch of feathery-looking things protruding from the tail end of the nudibranch are its gills, used for respiration. The gills can be retracted into a tiny pouch on the nudibranch's back. If you see one of these guys and it appears to have no gills, look for a little bump where the gills should be. That's where they are hidden.
Like many of its colorful cousins of the same genus, the Striped Pajama Nudibranch is a favorite photo subject for underwater macro photographers. No surprise there: it is colorful, photogenic -- and like most snails, it doesn't move very quickly. (Photographers are particularly fond of brightly colored critters that will hold still long enough to focus the lens!)
I photographed the individual on this page in the Red Sea at a place called Shark Bay, which is not far from Sharm el Sheikh, Egypt. [Click on the photo to enlarge.]