Okenia sapelona? from Brazil

Dear Vinicius,
Thanks for this interesting photo. I had always thought Okenia sapelona was most probably just a west Atlantic specimen of Okenia mediterranea  and on checking out the description while looking at your message I am even more convinced that it is. The animal is described as 'iridescent pale blue' which I assume means the animal was translucent whitish, and it had maroon rhinophores and maroon spots on the gills. The animal has yellow markings - as illustrated in black and grey stippling in the sketch alongside. Marcus & Marcus say it is closest to O. mediterranea but consider that that species differs in not having papillae in the dorsal midline. As can be seen in many photos on the Forum, O. mediterranea, like the Marcus sketch of O. sapelona, does have a median ridge with raised tubercles along its length. I suspect it is just one of many species found on both sides of the Atlantic. Another example which came to light through photos to the Forum is the west Atlantic speciesPolycera chilluna , which is almost certainly the same species as the  east Atlantic  Polycera aurantiomarginata. 

Which brings me back to your animal. It is possible taht it is the same as O. sapelona  but some differences make me hesitant. Although they both have the last pair of lateral papillae on each side sharing a joint base, the lateral papillae are much longer and fewer in number in your animal. Also, although their are similarities in colour, the bright blue bands on the lateral papillae and down the side of the head in your animal are quite different. It's possible that these are just part of the species' variability, but I would think it was worth checking the anatomy of your animal to see just how similar it is to more typical O. mediterranea.

ILLUSTRATION: Fig 2. Okenia sapelona from original description. Marcus, E. and E. Marcus. 1967. Some opisthobranchs from Sapelo Island, Georgia, U. S. A. Malacologia, 6: 199-222.

Best wishes,
Bill Rudman