Opisthobranch of the Week Data
[Note: Normally I would add to the above, a list of ranges for all Okinawa-collected specimens of the species, but due to the common occurrence of this animal on Okinawa, I have collected relatively few specimens and it would perhaps be counter-productive to attempt to furnish a range list for location, date, depth, and size on these animals.]
Plakobranchus ocellatus is found throughout the entire tropical/subtropical Indo-West Pacific and here on Okinawa it is very commonly found in water ranging from the intertidal to approximately five meters. Large numbers of P. ocellatus are found in most intertidal areas, especially lagoons (but not in live, dense stony coral reef environments). Many local divers miss seeing these well-camouflaged slugs due to their being frequently found lightly covered with silt and sand; often times they are found as divers "fin" through a shallow embayment and stir up the bottom sediments, and therefore the slugs themselves.
Plakobranchus ocellatus is a member of one of several major groups of opisthobranchs which have effectively evolved strategies to use the sun's energy directly for their own benefit. Bill Rudman refers to these groups as being "solar powered", and he has an excellent presentation on the adaption of these animals on the Slug Forum ( Solar-powered Sea Slugs ) as well as a listing of selected journal articles.
In a Slug Forum article concerned with Plakobranchus ocellatus, Bill proposes these animals may well deliberately shade their chloroplasts from the bright sun by covering the chloroplasts with their parapodia, to perhaps prevent the reception of potentially high amounts of light intensity.