This animal is colored a lot like what we call Elysia nigropunctata, but in our photos of that species the parapodia are very much reduced and topped with orange (although the original description of E. nigropunctata apparently does not mention the orange, which then would be a closer match to the one on this page). In the specimen below, the parapodia were wide and flaring, easily flopping back and forth in the light surge. Otherwise, the black spots along the parapodia and the color of the head are almost identical. They could simply be different growth forms of the same species. Indeed, Sea Slugs of Hawaii describes a similar difference between sedentary and migratory forms of Elysia marginata. The animal figured below is so far the only one like it known, and it was damaged when found, with a split running nearly the entire length of the body. Still, it seemed to be functioning ok. It was found exposed on hard substrate on a shallow Kwajalein Atoll lagoon pinnacle at a depth of about 6m on 25 October 2009, and it measured about 40mm in length.
The next photo shows the split along the body that was present when it was found.
Created 30 October 2009
Updated 3 February 2022