This strange sea slug combs sandy and silty sea bottoms for food with a large oral veil, which is fringed with tiny sensory "fingers" (papillae), though what it actually eats is not well known. It rests within the sand when inactive, and quickly burrows when threatened.
Euselenops luniceps belongs to the Pleurobranchidae, a family of sea slugs known as "side-gilled slugs" with the gill hidden on the right side of the body under the mantle (the body edge). Some pleurobranchs can be quite large, as long as 500mm! This species grows to 70mm, though the animal in this video is only ~25mm, about the size of a U.S. quarter.
While some sea slugs move slowly, E. luniceps is quite fast! The video is not sped up in any way -- this is the animal's natural speed. This one was so fast that keeping the focus and camera stability was very difficult, so image quality suffered a little.
The species is widespread throughout the Pacific, but it has net been recorded in Guam. This video was shot in Anilao, Philippines.