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This species is most likely as Phyllidia sp. 8 in Gosliner et al. (2015) at page 282, it might be as well a strange colour form of Phyllidia willani.
Pretty similar with a whitish granular appearance are:
Phyllidia ocellata which is very variable in colour, but has usually a yellow-orange ground colour of the mantle, and has large black rings,
Phyllidia babai which has a white granular appearance and black rings.
Phyllidia exquisita which has a pale bluish granular background colour, black swirls, and yellowish-orange pigment at the mantle margin
Phyllidia willani which lacks the Y-shaped black patch between the rhinophores.
I can't tell for sure how to distiguish the phyllidiids with the whitish granular appearance:
Phyllidia babai, Phyllidia exquisita, Phyllidia willani, Phyllidia sp. 01 and Phyllidia sp. 3 in IPN at page 292. I guess they are variants of one species.
Bill Rudman thinks Phyllidia babai, Phyllidia exquisita, and Phyllidia willani to be variants of the very variable Phyllidia ocellata.
More than 20 years after Brunckhorst (1993) needs the family Phyllidiidae Rafinesque, 1814 a worldwide revision based on anatomical and molecular studies, not like the recent publication Stoffels et al. (2016) which focusses on the "coral triangle" and excludes most oceans.
Brunckhorst, D.J. (1993) The systematics and phylogeny of Phyllidiid Nudibranchs (Doridoidea).
Records of the Australian Museum, Supplement 16: 1-107.
Gosliner, T.M, D.W. Behrens & Á.Valdés. 2015. Nudibranch &Sea Slug Identification Indo-Pacific.
New World Publications Inc. Jacksonville, FL. 408 pp.
Stoffels, B. E. M. W., van der Meij, S. E. T., Hoeksema, B. W., van Alphen, J., van Alen, T., Meyers-Muñoz, M. A., and van der Velde, G. (2016). Phylogenetic relationships within the Phyllidiidae (Opisthobranchia, Nudibranchia).
ZooKeys, (605), 1-35. Advance online publication. http://doi.org/10.3897/zookeys.605.7136
How to cite:
Köhler, E. (2019), published 16 April 2019, Phyllidia sp. 04 Genus: Cuvier, 1797
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Doridina/Phyllidia_sp_04.htm