Pleurobranchus areolatus is a sea slug from the family Pleurobranchidae.
It lives in Caribbean Sea, Brazil, Madeira and Canary Islands. Such distribution in western Atlantic and also in eastern Atlantic is called amphiatlantic (or amphi-Atlantic).
I thank my colleague Jessica Goodheart from the USA who kindly provided the photo.
This certain specimen of Pleurobranchus areolatus comes from Panama. You can find more information about sea slugs from Panama in her article “Identification guide to the heterobranch sea slugs (Mollusca: Gastropoda) from Bocas del Toro, Panama“.
This is the right side view of the slug. Its body is oval. There are numerous tubercles on the dorsum. Its rhinophores are in the frontal sinus. The gill is not visible because it is under the dorsum. There is also small internal shell inside the slug’s body, but the shell is not visible externally.
Goodheart J. A., Ellingson R. A., Vital X. G., Galvão Filho H. C., McCarthy J. B., Medrano S. M., Bhave V. J., García-Méndez K., Jiménez L. M., López G. & Hoover C. A. (2016). “Identification guide to the heterobranch sea slugs (Mollusca: Gastropoda) from Bocas del Toro, Panama“. Marine Biodiversity Records 9(1), p.56. doi:10.1186/s41200-016-0048-z