Phyllodesmium sp. 12
Locality: Old Woman Island, Mooloolaba, Sunshine Coast, 9 m, Queensland, Australia, Pacific Ocean, 29 November 2003, Subtidal. Length: 70 mm. Photographer: Gary Cobb.
Photographed with xeniid colony so probably a xeniid feeder. The only other other xeniid feeder with longitudinal ridges on the upper half of the cerata (vertical when cerata standing up) is Phyllodesmium rudmani, but in that species the ridges are all around the ceras while in your animal they only seem to be on the outer half. Similar to P. lizardensis but in that species the secondary ridges are really a series of nodules. However in both those species the ridges are covered in opaque white, meaning the brown speckling [which represents digestive gland branches filled with zooxanthellae] is restricted to the 'valleys' between the ridges. There is no white pigmentation in your animal and there appears to be brown pigmentation, in the ridges.
This is possibly another unnamed species of Phyllodesmium.Authorship details
Rudman, W.B., 2008 (September 3) Phyllodesmium sp. 12 [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/phyllodsp12
Re: The new Phyllodesmium lizardensis from sthn Queensland
From: Ingo Burghardt, September 3, 2008
The new Phyllodesmium lizardensis from sthn Queensland?
From: Gary Cobb, September 2, 2008