Cephalaspideans or headshield slugs are a group of sea slugs characterized by having a broad head often used to plow under the sediment and a headshiled which prevents the sand from entering the mantle cavity. They are often fierce predators of other marine invertebrates such as nudibranchs.

More info about this species:
www.seaslugforum.net/find/aglatric
hypselodoris.blogspot.pt/2012/03/aglaja-tricolorata-renie...