The Rusty Elysia is often found alongside or close to the Ornate Elysia and, at first, I found them quite difficult to tell apart.  Both have sendentary and migratory forms and orange margins.  Both have chimneys (or not depending on their form). The individuals documented in the gallery below were all found in less than 10 ft (2 metres) of water, in both protected areas and exposed surge zones.  For more information check out Sea Slugs of Hawaii.  To 2 inches (50 mm), though most individuals documented here were less than 20 mm (3/4 in).