This is not a common sight in the shallow waters around South Maui, where we usually snorkel, and so it is a pleasure to find.  It is relatively flat and thin with no tubercles, but it can still be mistaken for a juvenile or paler version of the Phyllidia varicosa. This animal was found in North Kihei in an area of broken reef, sand, rubble and sponges. To 2″ or 25 mm.  Please see Sea Slugs of Hawaii for more detailed information about its history and taxonomy, more photos, etc.