At first I found these Elysia marginata extremely difficult to tell apart from the Elysia rufescens (or Rusty Elysia). Apparently, this is because they are extremely variable and come in sedentary and migratory forms and often share the same territory as the rufescens.  Seek out Cory Pittman and Pauline Fiene’s Sea Slugs of Hawaii site if you’d like to know more.  All of the lighter individuals in the photographs above were quite small (6 mm to 20 mm) and, from what I can tell, of the migratory form (tall, thickish parapodia held in chimneys).  The two darker individuals were larger (50 mm or 2″).  I believe these are also of the migratory form, though much larger than usual?  All lighter animals were found in less than 2 metres of water feeding on green algae in protected rocky areas of North Kihei, Maui. Darker individuals were found in a surge zone filled with floating algae in the Po‘olenalena area of S. Maui, along with the eggs pictured above.