August 8, 2008
From: Gary Cobb
Concerning message #21756:
In regards to Phyllodesmium macphersonae cerata, I have attached two shots from two animals that, to me, clearly show cerata that are 'forked' [photos A, B]. And yes the appearance of forked cerata due to underlaying cerata are an illusion. Not all animals have this but the next one we find I will get some microscope shots for you to see.
Locality: Old Woman Island, Mooloolaba, Sunshine Coast, 12 m, Queensland, Australia, Pacific Ocean, 22 December 2005, Subtidal. Length: 6-18 mm. Photographer: Gary Cobb.
email@example.comCobb, G.C., 2008 (Aug 8) Re: Phyllodesmium macphersonae from sthn Queensland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21774
Certainly these two close-ups show strange branches off the main ceras. I looked carefully at the photos in your other message [#21756] and was pretty convinced that the apparent branching was from the tip of an underlying ceras. I've included here [ Photo C] a slight enlargement of the highest res photo you sent in your earlier message and I am sure the 'branch' in the lower right of the photo is the tip of a smaller underlying ceras. There is no indication of the digestive gland duct branching and I can see the unbroken left edge of the upper ceras. However the 'branch' in the upper left of that photo could well be a real branch.
It would be interesting to see microscope shots, just to see if there is in any indication of the digestive gland duct branching into the ceratal branch. Looking at your photo B, both the large cerata have a small ceras right beneath them whose tips could be mistaken for branches. So it looks as though some 'branches' can be illusions, and some can be real. As to why this branching occurs, I have no idea. The specimens in your photos were from two years apart so it seems to be a local phenomenon. If this species is a direct developer then perhaps it is a local genetic oddity, or perhaps there is some local pollutant which is interfering with their development.
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