Phyllidiella rudmani ? from Nthn Marianas Islands

Dear Harry,

I am afraid that all we have to go on from photos is the colour markings, and if they don't 'fit' the 'typical' pattern for a species, we have a problem. More importantly, I suspect we still have a bit to learn about colour variability in individual species. I agree that your animal is unlikely to be P. pipeki mainly because the rhinophores in that species have a distinct black band down the posterior side of the stalk. In your animals the upper half of the rhinophore is black and the lower half is pinkish white. There is a blackish tinge down the stalk but it seems to be an internal coloration.

The two most probable identifications are Phyllidiella rudmani and P. lizae. I feel a bit of a failure not being able to identify P. rudmani with confidence, but as I discuss in an earlier message [#19480] this species can have more than the chracteristic pair of black lines. In fact Brunckhorst, in his description, says there can be two extra lines near the edge, and 'additional black lines, if present, are less distinct and usually interrupted '.

The other species I mentioned, P. lizae, does have transverse lines as in your photos, but there is a distinctive diagonal black cross in the middle of the back and the longitudinal lines join both anteriorly and posteriorly. I can't really say which differences are more important, so my identification of your animals as P. rudmani is very tentative.

Best wishes,
Bill Rudman