Main image, Pikachu Nudibranch - Thecacera pacifica, by Rafi Amar

Thecacera pacifica is a species of Dorid nudibranch, It is also known as the Pikachu nudibranch!

Above, Photo by Connie Chen

It is found on the African coast of the Indian Ocean (Mozambique), Indonesia and Vanuatu. It has also been found on the Gulf of Mexico!

Above, Photo by Brian Mayes

They grow to around 2-3cm in length, and live underneath loose rock and sand!

A video of one wobbling around in the sea!

They also seem to have some variety in colour and patterning....!

Above, Photo by Francis Lau

Above, Photo by Ludovic

Info via wikipedia, and seaslugforum

edit- Once again I forgot to do the pop out image thing