This is the sea slug Limapontia capitata drawn for the Marine Research Centers at Stockholm and Umeå universities. Depicting it seemed like an easy task at first glance but proved to be quite a challange. I made use of my experience of painting semi-glossy and semi-transparent candy and added some salt to the wet paint to create the light dappled pattern.
Update January 21st, 2012:
Ian Smith kindly points out that this is Limapontia depressa, not Limapontia capitata. This mistake will be corrected as soon as possible.