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I asked Dr. Richard C. Willan "how variable is Phyllidiella rudmani?":
"As described has Phyllidiella rudmani two black longitudinal lines which do not unite, and pale pinkish-white rhinophores with a black upper half/tip. I have posted with some 'headache' specimens with a transverse black line." I asked as well about the picture taken by Martin Burman at Puerto Galera with black and white rhinophores but 4 (four) black lines. Here is Richard's answer (Pers comment):
"People have been asking this same question about the variability of Phyllidiella rudmani ever since David Brunckhorst published his monograph on the Phyllidiidae in 1993. Based on morphology plus my experience with other spp. of phyllidiids, P. rudmani is quite variable (that is, it can have either 2 or 4 longitudinal lines and there can sometimes be transverse lines connecting the 2 innermost longitudinal lines - so your 'headache' specimens would indeed be P. rudmani). This would be an example where genetics might help to decide if they are all the same species."
Pretty similar are:
Phyllidiella granulata which has a grey background colour with conical and acute compound white tubercles, and solid black rhinophores
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 cooraburrama which has very large, isolated, smooth, rounded tubercles which are pink.
Phyllidiella nigra which has single rounded dark pink to red tubercles on the black mantle.
Phyllidiella pustulosa which has grouped clusters of low tubercles and a pale pink mantle margin.
Phyllidiella rosans which has low, rounded, smooth, straight ridges. This species from the Indian Ocean has not yet been reported from the Philippines.
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 rudmani are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2018), published 17 February 2018, Phyllidiella rudmani Brunckhorst, 1993
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Phyllidiella_rudmani.htm