Opisthobranch of the Week Data
Phyllidia willani is considered to be uncommon on Okinawa; although only seven specimens have been collected as of early January 2000, a score or so of others have been seen and many of these photographed. The nearest appearing phyllidiid on Okinawa resembling P. willani is P. ocellata. However, in the case of P. ocellata, Rudman (1999) mentions that
"the dorsum is gold with black areas bordered in white and coloured tubercles which arise from the black areas. P. ocellata has a grey foot and grey oral tentacles with yellow tips (both pale cream in P. willani)."P. willani is distinguishable from other Okinawan phyllidiids by the two laterally positioned longitudinal black swirls of pigment on the the notum. Brunckhorst (1993) points out the presence of four large tubercles arranged as though at the corners of a diamond. These characters segregate P. willani from P. ocellata, as well as other similar appearing members of the group.
I've included images of three additional animals, showing some of the variation seen here within the species.
The species was named in honor of Dr. Richard C. Willan, of the Museum of the Northern Territory, Australia.