This is a rather large and common diurnal nudibranch and it is often found under reef edges and caves or snuggled into holes in spongy/rocky areas.  It can be a little difficult for the novice to distinguish between juvenile Phyllidia varicosa and some Sphinx Phyllidia as some varicosa can be entirely missing the identifying marker of yellow tubercles.  Younger ones can also appear much flatter than they are and with few tubercles.  Also referred to commonly as the Fried Egg Nudibranch (for obvious reasons0. For more information, please see Sea Slugs of Hawaii.  All animals photographed here were found in less than 20 ft of water (6 metres) in South Maui.  They were were anywhere from  25 mm to 100 mm (1″ to 4″).