Bighorn Nembrotha (Nembrotha megalocera).
This nudibranch is endemic to the Red Sea and it grows up to 7, 5 cm long. It’s fairly common and one of few that actually can “swim” like a fish by lateral flexing of the body when disturbed. The one on the picture is around 5 cm long.
The picture is taken on 20 meters depth on one of Deep South’s house reefs. When I found the nudibranch it was crawling on the coral but after a while it raised a big part of the body and “stood” up sniffing around. This apparently is its way to locate and find its way around the reefs. Since the region around the mouth, and its oral tentacles, are brimming with nerve endings, this is how it learns about its close environment. Without sight, it can only find out how big an obstacle in its path is by feeling around with its mouth and oral tentacles. The obstacle in this case was probably a big camera with an even bigger diver behind it. ;-)
