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Pretty similar are:
Phyllidiella cooraburrama which has very large, isolated, smooth, rounded tubercles which are pink.
Phyllidiella granulata which has a grey background colour with conical and acute compound white tubercles.
Phyllidiella lizae which has pale pinkish-white tubercles and narrow black lines which usually cross over the mantle forming an "X". The rhinophores are tipped black, then orange and white basally. These colours blend into each other.
Phyllidiella nigra which has single rounded dark pink to red tubercles on the black mantle.
Phyllidiella rosans which has low, rounded, smooth, straight ridges. This species from the Indian Ocean has not yet been reported from the Philippines.
Phyllidiella rudmani which has a pale pinkish-white mantle and two black lines. The pale pinkish-white rhinophores are tipped black.
Phyllidiella zeylanica which has highly tuberculate ridges which join together anteriorly and posteriorly.
Phyllidiopsis burni which has black rhinophores, a characteristical tapering of the body anteriorly and posteriorly, a black background coloration of the mantle, deep pink multicompound tubercles and a smooth translucent pink mantle edge.
Phyllidiopsis fissurata which has black background colouration and many tall pale pink tubercles. The rhinophores are pink with a black tip and a black line down posterior edge. It has a smooth tall raised pink anal papilla.
Phyllidiopsis krempfi which has rhinophores pink on anterior face and around base, black on apex and posterior face and a predominantly pink background coloration with broad based multicompound tubercles with paler apices. Apart from two primary longitudinal black lines, other black lines of variable size occur irregularly.
Phyllidiopsis pipeki which has bright pink colouration and consistently two straight black longitudinal lines only, rounded white tubercles (not multicompound). The rhinophores are pink with a black tip and a black line down posterior edge.
More information on Phyllidiella pustulosa are on Bill Rudman's Sea-Slug Forum!