Known from the South China Sea, the Philippines and Papua New Guinea.
11 m depth, Anemone Reef, Madang, PNG, 10 Jan. 1988, dorsal view of 36 mm specimen (note granular appearance), Photo: R.C. Willan (Brunckhorst, 1993: Plate 3F).
Notes compiled from Brunckhorst, 1993:
Distinguishing features of Phyllidia willani include the pale granular background coloration, the two laterally positioned longitudinal black swirls, the four median notal tubercles, the pale coloured foot and oral tentacles, orange digestive gland mass, pale yellow rectum, and small fine penial spines.
It is most similar to Phyllidia ocellata and Phyllidia babai. In contrast to P. willani, the dorsum of P. ocellata 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). Mature specimens of P. willani have 16-18 lamellae on the rhinophoral clavus whereas those of P. ocellata have 27-30 lamellae. The dorsum of P. babai has a white background and the mantle margin is bordered in yellow. In contrast, P. willani has a pale granular dorsum and no contrasting coloured edge to the mantle. The small species, Phyllidia exquisita, has white, black and yellow coloration. However, it differs from the present species in its possession of a yellow mantle margin, numerous rows of single tubercles, longitudinal and transverse black lines, and two lateral bands of white. Although P. willani is a larger species, it has fewer lamellae on the rhinophoral clavus than has the smaller P. exquisita.
• Brunckhorst, D.J. (1993) The systematics and phylogeny of Phyllidiid Nudibranchs (Doridoidea). Records of the Australian Museum, Supplement 16: 1-107.
Rudman, W.B., 1999 (January 12) Phyllidia willani Brunckhorst, 1993. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/phylwill