Flabellina rubrolineata

This species can be found over the whole Indo-Pacific region including the Red Sea. Most examples I have come across have been no more than 20 mm or so but reported to be up to 35mm in length.

This example was photographed at "Car Cemetery", Khorfakkan off the east coast of UAE.

I found this one on a night dive a Puerto Galera, Philippines, it appears to be balancing on a tightrope.

Below: Photographed in Lembeh Straits, Sulawesi, Indonesia (Nikon D7100, 60mm Micro lens)