Opisthobranch of the Week Data
I've not personally seen Phyllidia sp. 1 here in the waters of Okinawa's main island, however Atsushi Ono mentions (pers. comm.) that the above featured animal is but one of over ten individuals seen each year during the years 2000 to 2004, at a single locale in the Keramas* (at a particular dive site off Zamami Island) and considers the species to be uncommon there.
Currently there are two superficially similar appearing Phyllidia species having relatively large black solid dorsal spots found in Okinawan waters, P. polkadotsa and P. scottjohnsoni. Bill Rudman has an additional black spotted animal of another genus, Phyllidiopsis loricata, not yet reported from Okinawan waters, featured on the Sea Slug Forum which is also superficially similar to Phyllidia sp. 1. However, Phyllidia sp. 1 is externally distinctive enough from the preceding phyllidiids to suggest this is perhaps an undescribed species.
I've added a second page with an additional image of a 7mm specimen, also kindly furnished by Atsushi.